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Document and Entity Information - shares	6 Months Ended
Document and Entity Information - shares	Jun. 30, 2017	Jul. 28, 2017
Document and Entity Information
Entity Registrant Name	Mirna Therapeutics, Inc.
Entity Central Index Key	0001527599
Document Type	10-Q
Document Period End Date	Jun. 30, 2017
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		20,859,224
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	Q2

Condensed Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Current Assets:
Cash and cash equivalents	$ 15,219	$ 16,432
Short-term marketable securities	32,502	44,066
Prepaid expenses and other current assets	387	882
Total current assets	48,108	61,380
Property and equipment, net	13	354
Restricted cash	0	2,432
Total assets	48,121	64,166
Current Liabilities:
Accounts payable	47	361
Accrued expenses	1,375	2,400
Total current liabilities	1,422	2,761
Lease obligations, long-term	0	1,053
Total liabilities	1,422	3,814
Stockholders’ Equity (Deficit):
Preferred stock, $0.001 par value, 5,000,000 shares authorized at June 30, 2017 and December 31, 2016; 0 shares outstanding at June 30, 2017 and December 31, 2016	0	0
Common stock, $0.001 par value; 250,000,000 shares authorized at June 30, 2017 and December 31, 2016; 20,856,693 and 20,841,393 shares issued and outstanding at June 30 and December 31, 2016, respectively	21	21
Additional paid in capital	163,847	163,126
Accumulated deficit	(117,152)	(102,791)
Other comprehensive loss	(17)	(4)
Total stockholders’ equity	46,699	60,352
Total liabilities and stockholders’ equity	$ 48,121	$ 64,166

Condensed Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Preferred stock, par value (in USD per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	5,000,000	5,000,000
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in USD per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	250,000,000	250,000,000
Common stock, shares issued (in shares)	20,856,693	20,841,393
Common stock, shares outstanding (in shares)	20,856,693	20,841,393

Condensed Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Operating expenses:
Research and development	$ 5,079	$ 3,682	$ 5,321	$ 8,205
General and administrative	4,232	2,049	6,496	4,179
Restructuring charges	165	0	2,723	0
Total operating expenses	9,476	5,731	14,540	12,384
Other income:
Interest income	95	93	182	175
Net loss attributable to common stockholders	(9,381)	(5,638)	(14,358)	(12,209)
Other comprehensive loss:
Unrealized gain/ (loss) on available for sale securities, net of tax	0	(3)	(13)	6
Total other comprehensive loss	$ (9,381)	$ (5,641)	$ (14,371)	$ (12,203)
Net loss per share attributable to common stockholders—basic and diluted (in USD per share)	$ (0.45)	$ (0.27)	$ (0.69)	$ (0.59)
Common shares used to compute basic and diluted net loss per share attributable to common stockholders (in shares)	20,856,693	20,831,723	20,853,628	20,831,139

Condensed Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Operating activities
Net loss	$ (14,358)	$ (12,209)
Adjustment to reconcile net loss to net cash used in operating activities:
Restructuring charges	2,723	0
Depreciation and amortization	18	45
Stock-based compensation	693	689
Net amortization of premium/ discounts on marketable securities	127	98
Changes in operating assets and liabilities:
Prepaid expenses and other assets	496	(118)
Accounts payable	(314)	(2,584)
Accrued expenses	(4,801)	(21)
Net cash used in operating activities	(15,416)	(14,100)
Investing activities
Purchases of marketable securities	(27,528)	(50,848)
Maturities of marketable securities	38,952	9,000
Change in restricted cash	2,432	(2,430)
Proceeds from the sale of equipment	325	0
Purchases of property and equipment	(3)	(548)
Net cash provided by/ (used in) investing activities	14,178	(44,826)
Financing activities
Proceeds from the exercise of stock options	25	9
Cash provided by financing activities	25	9
Net decrease in cash and cash equivalents	(1,213)	(58,917)
Cash and cash equivalents at beginning of period	16,432	89,713
Cash and cash equivalents at end of period	$ 15,219	$ 30,796

Nature of Business and Basis of Presentation	6 Months Ended
Nature of Business and Basis of Presentation	Jun. 30, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Business and Basis of Presentation	Nature of Business and Basis of Presentation Nature of business Mirna Therapeutics, Inc. (“Mirna” or “the Company”) is a biopharmaceutical company that has historically focused on microRNA-based oncology therapeutics. The Company was incorporated in Delaware in December 2007 as a wholly‑owned subsidiary of Asuragen, Inc. (“Asuragen”) and was spun out to existing Asuragen stockholders in December 2009. The Company is located in Austin, Texas. Following the close of the Company's Phase 1 clinical trial of MRX34 in September 2016, the Company began to evaluate its strategic alternatives focusing on enhancing stockholder value, including the possibility of a merger or sale of the Company. Mirna has discontinued further research and development activities (see Note 10) to reduce operating expenses while it evaluates these opportunities. In May 2017, the Company and Synlogic Inc., a Delaware corporation (“Synlogic”), entered into an Agreement and Plan of Merger and Reorganization (the “Merger Agreement”), pursuant to which, among other matters, and subject to the satisfaction or waiver of the conditions set forth in the Merger Agreement, a wholly-owned subsidiary of Mirna will merge with and into Synlogic, with Synlogic surviving as a wholly-owned subsidiary of Mirna (the “Merger”), subject to the terms of the Merger Agreement and stockholder approval of the transaction. See Note 3 below for more information regarding the Merger. The Company continues to be subject to a number of risks common to companies in similar stages of development. Principal among these risks are uncertainties of technological innovations, dependence on key individuals, development of the same or similar technological innovations by the Company’s competitors and protection of proprietary technology. The Company believes that its cash, cash equivalents and marketable securities of $47.7 million at June 30, 2017 will enable the Company to maintain its current and planned operations for at least the next 12 months. Basis of presentation The accompanying interim condensed financial statements as of June 30, 2017 and for three and six months ended June 30, 2017 and 2016, and the related interim information contained within the notes to the financial statements, are unaudited. The unaudited interim condensed financial statements of Mirna have been prepared in accordance with generally accepted accounting principles for interim financial information on a stand-alone basis without giving effect to the Merger and on the same basis as the audited financial statements. In the opinion of management, the accompanying unaudited interim condensed financial statements contain all adjustments which include only normal recurring adjustments necessary to state fairly the Company’s financial position as of June 30, 2017, and the results of its operations and cash flows for the interim periods ended June 30, 2017 and 2016. Such adjustments are of a normal and recurring nature. The interim financial data as of June 30, 2017 is not necessarily indicative of the results to be expected for the year ending December 31, 2017, or for any future period. The accompanying condensed financial statements and related financial information should be read in conjunction with the audited financial statements and related notes thereto for the year ended December 31, 2016 included in the Company’s Form 10-K, filed with the U.S. Securities and Exchange Commission (the "SEC") on March 15, 2017.

Summary of Significant Accounting Policies

6 Months Ended

Jun. 30, 2017

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

Use of estimates

The preparation of financial statements in conformity with U.S. generally accepted accounting principles requires the Company’s management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Amounts included in the financial statements, such those recorded in restructuring charges, can result from a complex series of judgments about future events and uncertainties and can heavily rely on estimates and assumptions. Actual results could differ from those estimates.

Research and development costs

Research and development costs are expensed as incurred. Research and development costs include salaries and personnel‑related costs, consulting fees, fees paid for contract research services, the costs of laboratory equipment and facilities, development of intellectual property, license fees and other external costs. The Company accounts for government grants as a reduction of research and development expenses. Government grants are recorded at the time the related research and development costs have been incurred by the Company and, accordingly, become eligible for reimbursement. The Company accrues for government grants that have been earned but not yet received.

Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are deferred and capitalized. The capitalized amounts are expensed as the related goods are delivered or the services are performed.

Clinical Trial and Pre-Clinical Study Accruals

Prior to the discontinuation of the Company's research and development activities, the Company estimated pre-clinical study and clinical trial expenses pursuant to contracts with research institutions and contract research organizations that conducted and managed pre-clinical studies and clinical trials on the Company’s behalf. These estimates were based on the level of service performed and the underlying agreement. Further, the Company accrued expenses related to clinical trials based on the level of patient enrollment and other activities according to the related agreements. The Company monitored patient enrollment levels and other activities to the extent reasonably possible and adjusted estimates accordingly. If actual costs incurred or the timing of services varied from the Company's estimate, the Company adjusted the accrual accordingly. On September 20, 2016, the Company announced its decision to close the ongoing Phase 1 study of MRX34 and suspended all research and development activities.

Stock‑based compensation

The Company accounts for its stock‑based compensation awards in accordance with ASC Topic 718, Compensation—Stock Compensation (“ASC 718”). ASC 718 requires all stock‑based payments to employees, including grants of employee stock options, to be recognized in the statements of operations based on their grant date fair values. For stock options granted to employees and to members of the board of directors for their services on the board of directors, the Company estimates the grant date fair value of each option award using the Black‑Scholes option‑pricing model. The use of the Black‑Scholes option‑pricing model requires management to make assumptions with respect to the expected term of the option, the expected volatility of the common stock consistent with the expected life of the option, risk‑free interest rates and expected dividend yields of the common stock. For awards subject to service‑based vesting conditions, the Company recognizes stock‑based compensation expense equal to the grant date fair value of stock options on a straight‑line basis over the requisite service period less actual forfeitures.

Restructuring charges

Following the closing of the Phase 1 MRX34 clinical trial, the Company implemented a workforce reduction in the fourth quarter of 2016 to reduce operating expenses while it evaluates strategic alternatives. The majority of severance and benefits payments were settled during the first quarter of 2017. The Company entered into retention agreements with key employees necessary to close the Phase 1 clinical trial of MRX34 and maintain the continued operations of the Company. Under the retention agreements, employees must remain with the Company until June 30, 2017 or until terminated by the Company without cause prior to such date. The Company has recognized the restructuring liability for such retention agreements over each employee's service period.

In accordance with ASC 420, Exit and Disposal Cost Obligations, the Company has also recognized contract termination costs in connection with a leased property it intended to occupy as its corporate headquarters and research facility, as well as a temporary lab in use prior to the discontinuation of the Company's research and development activities. In addition, the Company has recognized asset impairments related to its lab equipment used in the Phase 1 clinical trial, construction in process, and other property and equipment for which the Company does not expect to receive a future benefit.

Fair value measurements

The Company records money market funds at fair value. ASC Topic 820, Fair Value Measurements and Disclosures, establishes a fair value hierarchy for those instruments measured at fair value that distinguishes between assumptions based on market data (observable inputs) and the Company’s own assumptions (unobservable inputs). The hierarchy consists of three levels:


•	Level 1 – Unadjusted prices in active markets for identical assets or liabilities.


•	Level 2 – Quoted prices for similar assets and liabilities in active markets, quoted prices in markets that are not active, or inputs which are observable, either directly or indirectly, for substantially the full term of the asset or liability.


•	Level 3 – Unobservable inputs that reflect the Company’s own assumptions about the assumptions market participants would use in pricing the asset or liability in which there is little, if any, market activity for the asset or liability at the measurement date.

The carrying amounts reflected in the balance sheets for cash, prepaid expenses and other current assets, accounts payable, and accrued expenses approximate their fair values at June 30, 2017 and December 31, 2016, due to their short‑term nature.

The Company evaluates transfers between levels at the end of each reporting period. There were no transfers of assets or liabilities between Level 1, Level 2 or Level 3 during the six months ended June 30, 2017 or 2016.

Restricted Cash

Restricted cash consisted of cash amounts held for specific or limited purposes and, therefore, not available for general operating activities. In June 2016, the Company secured a standby letter of credit of $2.4 million for the benefit of the Landlord for the Company's lease of approximately 23,578 square feet of office and laboratory space in the event of default. The restricted cash consists of cash providing security under the terms of the G&I Lease described in Note 11.

As a result of the Lease Settlement described in Note 11, the Landlord has released the letter of credit described above to the Company and the balance of restricted cash has been reclassified to cash and cash equivalents at June 30, 2017.

Marketable Securities

Marketable securities with maturities at purchase beyond one year, but less than twenty-four months, may be classified as short-term marketable securities based on their highly liquid nature and because such marketable securities represent the investment of cash that is available for current operations. Marketable securities with maturities at purchase beyond twenty-four months are classified as non-current. Available-for-sale securities are maintained by an investment manager and may consist of U.S. Treasury securities and government agency securities and corporate debt securities. Available-for-sale securities are carried at fair value with the unrealized gains and losses included in other comprehensive loss as a component of stockholders’ equity until realized. Any premium or discount arising at purchase is amortized and/or accreted to interest income and/or expense over the life of the instrument. Realized gains and losses are determined using the specific identification method and are included in other income.

If any adjustment to fair value reflects a decline in value of the investment, the Company considers all available evidence to evaluate the extent to which the decline is “other-than-temporary.” If the decline is other-than-temporary, the investment is marked to market through a charge to the Company’s statement of operations and comprehensive loss.

Recently Adopted Accounting Pronouncements

In March 2016, the Financial Accounting Standards Board (FASB) issued ASU 2016-09, Compensation - Stock Compensation (Topic 718): Improvements to Employee Share Based Payment Accounting ("ASU 2016-09") as part of the FASB simplification initiative. The new standard provides for changes to accounting for stock compensation including 1) excess tax benefits and tax deficiencies related to share-based payment awards will be recognized as income tax expense in the reporting period in which they occur; 2) excess tax benefits will be classified as an operating activity in the statement of cash flow; 3) the option to elect to estimate forfeitures or account for them when they occur; and 4) increase tax withholding requirements threshold to qualify for equity classification. We adopted ASU 2016-09 in the quarter ended March 31, 2017 with an effective date of January 1, 2017 and made a policy election to account for forfeitures as they occur. In addition, the Company increased both its net operating loss deferred tax asset and its valuation allowance upon adoption of ASU 2016-09. This did not have an impact on net stockholders' equity as the incremental deferred tax assets were fully offset by a corresponding increase in the deferred tax asset valuation allowance as of March 31, 2017. The cumulative effect of adoption was recorded in the quarter ended March 31, 2017 and did not have a material impact on our condensed financial statements.

Merger Agreement	6 Months Ended
Merger Agreement	Jun. 30, 2017
Business Combinations [Abstract]
Merger Agreement	Merger Agreement On May 15, 2017, Mirna, Meerkat Merger Sub, Inc., a Delaware corporation and a wholly-owned subsidiary of Mirna (“Merger Sub”), and Synlogic, entered into the Merger Agreement, pursuant to which, among other matters, and subject to the satisfaction or waiver of the conditions set forth in the Merger Agreement, at the effective time of the Merger, Merger Sub will merge with and into Synlogic, with Synlogic continuing as a wholly owned subsidiary of Mirna and the surviving corporation of the Merger. The Merger is intended to qualify for federal income tax purposes as a tax-free reorganization under the provisions of Section 368(a) of the Internal Revenue Code of 1986, as amended (the “Code”). Subject to the terms and conditions of the Merger Agreement, at the effective time of the Merger, (a) each outstanding share of Synlogic common stock and Synlogic preferred stock will be converted into the right to receive a number of shares of Mirna’s common stock equal to the exchange ratio (as described in the Merger Agreement); and (b) each outstanding Synlogic stock option that has not previously been exercised prior to the effective time of the Merger will be assumed by Mirna. Pursuant to the exchange ratio formula in the Merger Agreement, as of immediately after the Merger, the former Synlogic securityholders are expected to own approximately 83% of the outstanding shares of Mirna's common stock on a fully-diluted basis and securityholders of Mirna as of immediately prior to the Merger are expected to own approximately 17% of the outstanding shares of Mirna's common stock on a fully-diluted basis. The exchange ratio will be adjusted to the extent that Mirna’s net cash at closing is greater than or less than $40 million, as of immediately prior to the effective time of the Merger, as described further in the Merger Agreement. Consummation of the Merger is subject to certain closing conditions, including, among other things, approval by the stockholders of Mirna and Synlogic, and Mirna’s satisfaction of a minimum net cash threshold of $33.5 million immediately prior to the effective time of the Merger. In accordance with the terms of the Merger Agreement, (i) certain executive officers, directors and stockholders of Synlogic (solely in their respective capacities as Synlogic stockholders) holding approximately 77% of the shares of outstanding Synlogic capital stock (after giving effect to Synlogic’s Series C financing) have entered into support agreements with Mirna to vote all of their shares of Synlogic capital stock in favor of adoption of the Merger Agreement and approval of the transactions contemplated by the Merger Agreement (the “Synlogic Support Agreements”) and (ii) certain executive officers, directors and stockholders of Mirna (solely in their respective capacities as Mirna stockholders) holding approximately 33% of the outstanding shares of Mirna's common stock have entered into support agreements with Synlogic to vote all of their shares of Mirna common stock in favor of adoption of the Merger Agreement and approval of the transactions contemplated by the Merger Agreement (together with the Synlogic Support Agreements, the “Support Agreements”). The Support Agreements include covenants with respect to the voting of such shares in favor of approving the transactions contemplated by the Merger Agreement and against any competing acquisition proposals and place certain restrictions on the transfer of the shares of Mirna and Synlogic held by the respective signatories thereto. Concurrently with the execution of the Merger Agreement, certain officers, directors and stockholders of Mirna holding approximately 33% of the outstanding shares of Mirna common stock and certain officers, directors and stockholders of Synlogic holding approximately 81% of the outstanding shares of Synlogic capital stock (giving effect to Synlogic’s Series C financing) have entered into lock-up agreements pursuant to which, among other things, they have accepted certain restrictions on the transfer of shares of our common stock during the 180-day period following the closing of the Merger. The Merger Agreement contains certain termination rights for both Mirna and Synlogic, and further provides that, upon termination of the Merger Agreement under specified circumstances, either party may be required to pay the other party a termination fee of $2.0 million, or in some circumstances reimburse the other party’s expenses up to a maximum of $1.0 million. At the effective time of the Merger, the board of directors of Mirna is expected to consist of seven members, five of whom will be designated by Synlogic and two of whom will be designated by Mirna.

Marketable Securities

6 Months Ended

Jun. 30, 2017

Investments, Debt and Equity Securities [Abstract]

Marketable Securities

The following table summarizes the available-for-sale securities held at June 30, 2017 and December 31, 2016 (in thousands):



	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
June 30, 2017
U.S. government agency securities and treasuries	$	32,519	$	—	$	(17	)	$	32,502
Total available-for-sale securities	$	32,519	$	—	$	(17	)	$	32,502



	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
December 31, 2016
U.S. government agency securities and treasuries	$	42,516	$	4	$	(8	)	$	42,512
Corporate debt securities	1,554		—		—			1,554
Total available-for-sale securities	$	44,070	$	4	$	(8	)	$	44,066

There were no available-for-sale securities held as of June 30, 2017 that had remaining maturities greater than one year.

- Definition

Tabular disclosure of available-for-sale securities which includes, but is not limited to, changes in the cost basis and fair value, fair value and gross unrealized gain (loss), fair values by type of security, contractual maturity and classification, amortized cost basis, contracts to acquire securities to be accounted for as available-for-sale, debt maturities, transfers to trading, change in net unrealized holding gain (loss) net of tax, continuous unrealized loss position fair value, aggregate losses qualitative disclosures, other than temporary impairment (OTTI) losses or other disclosures related to available for sale securities.

+ References + Details

Fair Value Measurements

6 Months Ended

Jun. 30, 2017

Fair Value Disclosures [Abstract]

Fair Value Measurements

The following table sets forth the Company’s assets that are measured at fair value on a recurring basis as of June 30, 2017 and December 31, 2016 (in thousands):



	Total		Quoted prices in active markets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)
June 30, 2017
Assets:
Cash and cash equivalents
Cash	$	4,061	$	4,061	$	—	$	—
Money market funds	$	11,158	$	11,158	$	—	$	—
Total cash and cash equivalents	15,219		15,219		—		—
Marketable securities
U.S. government agency securities and treasuries	32,502		—		32,502		—
Total fair value financial instruments	$	47,721	$	15,219	$	32,502	$	—



	Total		Quoted prices in active markets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)
December 31, 2016
Assets:
Cash and cash equivalents
Cash	$	2,785	$	2,785	$	—	$	—
Money market funds	$	9,647	$	9,647	$	—	$	—
US government agency securities and treasuries	$	4,000	—		4,000
Total cash and cash equivalents	16,432		12,432		4,000		—
Marketable securities
U.S. government agency securities and treasuries	42,512		—		42,512		—
Corporate debt securities	1,554		—		1,554		—
Total marketable securities	44,066		—		44,066		—
Restricted cash	2,432		2,432		—		—
Total fair value financial instruments	$	62,930	$	14,864	$	48,066	$	—

Cash and cash equivalents

The Company considers all highly liquid securities with original final maturities of three months or less from the date of purchase to be cash equivalents. As of June 30, 2017 and December 31, 2016, cash and cash equivalents are comprised of cash, money market accounts, and U.S. government agency securities and treasuries.

Marketable securities

The cost of available-for-sale securities is adjusted for amortization of premiums and accretion of discounts to maturity. At June 30, 2017 and December 31, 2016, the balance in the Company’s accumulated other comprehensive loss was composed solely of activity related to the Company’s available-for-sale marketable securities. The Company has not realized material gains or losses on sales of available-for-sale investment securities during any of the periods presented.

As of June 30, 2017, available for sale securities of approximately $32.5 million were in an unrealized loss position of approximately $17,000. The Company has the intent and ability to hold such securities until recovery. The Company determined that there were no material changes in the credit risk of the above investments. The Company did not hold any investments with an other-than-temporary impairment as of June 30, 2017 and December 31, 2016.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Property and Equipment

6 Months Ended

Jun. 30, 2017

Property, Plant and Equipment [Abstract]

Property and Equipment

Property and equipment consisted of the following (in thousands):



	June 30, 2017			December 31, 2016
Furniture, computers and equipment	$	44		$	385
Accumulated depreciation	(31		)	(31		)
	$	13		354

Depreciation expense was approximately $13,000 and $26,000 for the three months ended June 30, 2017 and 2016, respectively. Depreciation expense was approximately $18,000 and $45,000 for the six months ended June 30, 2017 and 2016.

In February 2017, the Company entered into an Asset Purchase Agreement for the sale of certain of the Company's lab equipment ("Lab Equipment") with a third party for cash consideration of $325,000. The selling price of the Lab Equipment approximated its book value at December 31, 2016.

Common Stock

6 Months Ended

Jun. 30, 2017

Stockholders' Equity Note [Abstract]

Common Stock

The Company’s common stock has the following characteristics:


•	The holders of shares of common stock are entitled to one vote for each share of common stock held at all meetings of stockholders.


•	The holders of shares of common stock are entitled to receive dividends, if and when declared by the Company’s board of directors. Since inception, no cash dividends have been declared.

Offerings

In September 2015, the Company and the Cancer Prevention and Research Institute of Texas (“CPRIT”) entered into a grant contract, effective as of June 1, 2014 (the "2014 Contract"), in connection with an award of approximately $16.8 million. The award was in the form of an agreement by CPRIT to purchase $16.8 million of shares of common stock of the Company in a private placement concurrent with the initial public offering of the Company’s common stock. On October 5, 2015, CPRIT purchased 2,395,010 shares of the Company’s common stock at $7.00 per share. Net proceeds from the private placement, after related transaction offering costs, were approximately $16.6 million.

In October 2015, the Company issued 6.25 million shares of common stock in an underwritten public offering, with a price of $7.00 per share. The underwriters purchased an additional 704,962 shares of the Company's common stock pursuant to their option to purchase additional shares. The Company received aggregate net proceeds of approximately $43.7 million in the public offering, after deducting the underwriting discounts and commissions and estimated offering expenses payable by the Company.

Stock Option Plans

6 Months Ended

Jun. 30, 2017

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Stock Option Plans

2008 Long Term Incentive Plan

During 2008, the Company adopted the 2008 Long Term Incentive Plan, which allows for incentive stock options for its employees and nonqualified stock options (inclusive of restricted stock units and stock appreciation rights) (the “2008 Plan”) for employees and nonemployees under which an aggregate of 330,582 stock options and stock purchase rights may be granted. In December 2013, the total number of shares of the Company's common stock available for grant under the 2008 Plan was increased by 224,200 to 554,782. In March 2014, the Company’s board of directors approved an increase of 115,153 shares available for grant pursuant to the 2008 Plan to 669,935. In March 2015, the total number of shares of the Company's common stock available for grant under the 2008 Plan was increased in conjunction with the Company’s offering of Series D preferred stock by 391,650 shares to 1,061,585. Options under the 2008 Plan have a maximum life of 10 years from the date of grant. Options vest at various intervals, as determined by the Company’s board of directors at the date of grant.

2015 Equity Incentive Plan

In August 2015, the Company’s board of directors approved the 2015 Equity Incentive Award Plan (the “2015 Plan”), which was effective in connection with the pricing of the IPO on September 30, 2015. The 2015 Plan provides for the granting of a variety of stock‑based compensation awards, including stock options, stock appreciation rights, restricted stock awards, restricted stock unit awards, deferred stock awards, dividend equivalent awards, stock payment awards, performance awards and other stock‑based awards. The 2015 Plan is the successor to the 2008 Plan and the 446,765 shares subject to options granted under the 2008 Plan at June 30, 2017 may be transferred to the 2015 Plan if awards thereunder terminate, expire or lapse for any reason without the delivery of shares to the holder thereof. As of June 30, 2017, 333,100 shares have been transferred from the 2008 Plan to the 2015 Plan for awards that have terminated, expired, or lapsed. Under the 2015 Plan, 1,671,800 shares of the Company’s common stock were initially authorized and reserved for issuance. In addition, 1,041,527 and 1,042,070 shares of the Company's common stock were authorized and reserved for issuance in the first quarter of 2016 and 2017. respectively, for a total of 4,088,497 shares of the Company's common stock authorized for grant under the 2015 Plan at June 30, 2017.

2015 Employee Stock Purchase Plan

In August 2015, the Company’s board of directors approved the 2015 Employee Stock Purchase Plan (the “ESPP”), which was effective in connection with the pricing of the IPO on September 30, 2015. The ESPP allows eligible employees to purchase shares of the Company’s common stock at a discount through payroll deductions of up to 15% of their eligible compensation, subject to any plan limitations. The ESPP generally provides for set offering periods, and at the end of each offering period, employees are able to purchase shares at 85% of the lower of the fair market value of the Company’s common stock on the first trading day of the offering period or on the last trading day of the offering period. Shares available for future purchase under the ESPP were 369,960 at June 30, 2017; however, as of December 2016, the Company has suspended future issuances of the Company's common stock under the ESPP plan.

Stock Option Activity

The Company’s stock option activity for the six months ended June 30, 2017 was as follows:



			Weighted‑
			Average		Weighted‑Average
	Number		Exercise		Contractual
	of Shares		Price		Life (years)
Outstanding at December 31, 2016	1,905,214		$	5.39	7.49
Granted	—		—
Exercised	(15,300	)	1.65
Forfeited/canceled	(302,040	)	5.46
Outstanding at June 30, 2017	1,587,874		$	5.41	7.80
Options exercisable at June 30, 2017	1,134,680		$	5.24	7.58

Stock Compensation Expense

Total stock-based compensation expense for the three and six months ended June 30, 2017 was recognized as follows in the statements of comprehensive loss (in thousands):



	Three Months Ended June 30,					Six Months Ended June 30,
	2017		2016			2017		2016
Research and development expense	$	30	$	(56	)	$	71	$	115
General and administrative expense	299		298			622		574
Total stock based compensation	$	329	$	242		$	693	$	689

As of June 30, 2017, there was approximately $1.7 million of unrecognized compensation cost related to the stock options granted under the 2015 Plan, which is expected to be amortized over a weighted-average period of 2.1 years. There were no restricted stock units or stock appreciation rights granted under the 2015 Plan as of June 30, 2017.

Income Taxes	6 Months Ended
Income Taxes	Jun. 30, 2017
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The Company has not recorded a provision for income taxes as of June 30, 2017 due to reported net losses since inception. During the six months ended June 30, 2017 and 2016, the Company had no interest and penalties related to income taxes. Deferred income taxes reflect the net tax effects of temporary differences between the carrying amount of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. The Company has established a valuation allowance due to uncertainties regarding the realization of deferred tax assets based upon the Company’s lack of earnings history. The Company files income tax returns in the U.S. federal and Texas jurisdictions. The statute of limitations for assessment by the Internal Revenue Service (“IRS”) is open for tax years ending December 31, 2015, 2014, and 2013, although carryforward attributes that were generated for tax years prior to 2013 may still be adjusted upon examination by the IRS if they either have been, or will be, used in a future period. The 2010 and subsequent tax years remain open and subject to examination by the State of Texas. There are currently no federal or state income tax audits in progress.

Restructuring Charges

6 Months Ended

Jun. 30, 2017

Restructuring and Related Activities [Abstract]

Restructuring Charges

On September 20, 2016, Mirna announced its decision to close the ongoing Phase 1 study of MRX34 and voluntarily halted the enrollment and dosing of patients in the study. Following the announcement, the Company received verbal notice from the U.S. Food and Drug Administration ("FDA") on September 28, 2016 that its Investigational New Drug MRX34 had been placed on full clinical hold. Following the Company's announcement and notification from the FDA, the Company's board of directors approved a reduction of the total number of full-time employees from 36 to 12. As of June 30, 2017, the total number of full-time employees was 4. The Company also committed to retention payments to certain key employees if such employees remained with the Company until June 30, 2017 or were terminated by Mirna without cause prior to such date. Total restructuring charges recognized under the plan totaled $7.2 million, of which $4.4 million was recognized during the year ended December 31, 2016 and included a non-cash impairment charge of $1.4 million.

Restructuring charges were as follows (in thousands):



	Three months ended June 30,			Six months ended June 30,
	2017		2016	2017		2016
Employee severance and related costs	$	43	—	$	248	—
Contract termination costs	122		—	2,475		—
Total restructuring charges	$	165	—	$	2,723	—

The accrued restructuring activity for the six months ended June 30, 2017 was as follows (in thousands):



	Employee severance and related costs			Contract Termination Costs			Total
Balance at December 31, 2016	$	1,097		$	1,565		$	2,662
Restructuring charges and adjustments	248			2,475			2,723
Cash payments	(1,234		)	(4,040		)	(5,274		)
Balance at June 30, 2017	$	111		$	—		$	111

Employee severance and related costs

Employee severance and benefits costs recorded in restructuring charges for the three and six months ended June 30, 2017 included $43,000 and $248,000 in accrued retention costs, which have been ratably recognized over the respective employee's service period.

Contract termination costs

Contract termination costs recorded in restructuring charges for the year ended December 31, 2016 of $1.5 million related to the Company's determination to cease use and not occupy the Company's headquarters and research facility in connection with the G&I Lease (see Note 11). In connection with this determination, the Company recorded a liability of $1.6 million, which was equal to the fair value of the lease obligation at the cease-use date of November 20, 2016. The Company estimated the liability for the contract termination costs associated with the G&I Lease as of the cease-use date based on the discounted present value of the remaining lease payments, considering future estimated sublease income, estimated broker fees and contractual executory costs.

In May 2017, the Company and its landlord entered into the Lease Settlement (defined in Note 11) to terminate the G&I Lease for consideration of approximately $3.8 million (the "Settlement Amount"). The Lease Settlement was contingent upon the Landlord's execution of a new lease with a third party. On June 23, 2017, the termination of the G&I Lease became effective upon entry by the Landlord into an agreement with a third party regarding the premises previously covered under the G&I Lease with the Company. The Company adjusted its liability for contract termination costs to the Settlement Amount and G&I Lease expenses incurred through the effective date, resulting in an adjustment of $2.5 million recorded in restructuring charges for the six months ended June 30, 2017. See Note 11 for additional discussion surrounding the termination of the G&I Lease.

Asset impairment costs

Following the discontinuation of research and development activities and corresponding workforce reduction, the Company determined that certain property and equipment was impaired and recognized an impairment charge of $1.4 million in restructuring charges in the statement of operations for the year ended December 31, 2016. Of the total impairment charge, approximately $555,000 relates to the impairment of the Lab Equipment which was sold for $325,000 in February 2017 (see Note 6). In addition, the Company recognized an impairment of $591,000 during the year ended December 31, 2016 in construction in progress for the Company's planned headquarters and research facility associated with the termination of the G&I Lease discussed above. Further, following the workforce reduction, the Company sold or donated its remaining office equipment with the exception of nominal office equipment necessary to continue administrative functions and the closure of its Phase 1 clinical trial, resulting in an impairment of furniture, computers and equipment and leasehold improvements of $256,000 recognized during the year ended December 31, 2016.

Commitments and Contingencies	6 Months Ended
Commitments and Contingencies	Jun. 30, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Operating Lease In June 2016, the Company and G&I VII Encino Trace II LP (the “Landlord”) entered into a lease for the Company's corporate headquarters and research facility in Austin, Texas (the “Headquarters”) under an operating lease agreement (the “G&I Lease”). The initial term of the G&I Lease was for a 123-month period, with the option to extend the G&I Lease for up to two consecutive 60-month terms. In November 2016, following the workforce reduction described in Note 10, the Company determined not to occupy and ceased use of the headquarters and research facility under the G&I Lease. See Note 10 to the financial statements for further information on accounting for the G&I Lease. The G&I Lease provides annual base rent of approximately $600,000 in the first year after a three-month rent free period following January 1, 2017, the commencement date of the G&I Lease. with subsequent annual increases of approximately 3% in the annual base rent. In connection with the G&I Lease, the landlord has provided a tenant improvement allowance of approximately $1.9 million to be used by the Company to build-out certain improvements to the Headquarters. There have been no draws on the improvement allowance as of June 30, 2017. In connection with the G&I Lease, Mirna obtained a standby letter of credit (the “Letter of Credit”) for the initial amount of approximately $2.4 million, which the Landlord may draw down in the event of default. In May 2017, the Company and the Landlord entered into a Lease Termination Agreement and Release (the “Lease Settlement”) to terminate the G&I Lease for consideration equal to the Settlement Amount. In June 2017, the termination of the G&I Lease became effective upon entry by the Landlord into an agreement with a third party regarding the premises previously covered under the G&I Lease. The Lease Settlement includes standard representations and warranties and released both the Company and the Landlord from their mutual obligations under the G&I Lease, provided, for purposes of the Landlord's release, the Company does not file for bankruptcy or otherwise make an assignment for the benefit of creditors within 90 days of the Landlord's receipt of the Settlement Amount. In June 2017, the Landlord released the Letter of Credit to the Company and the balance of restricted cash was reclassified to cash and cash equivalents at June 30, 2017. There were no draws on the Letter of Credit at any time during which it was outstanding. CPRIT In August 2010, the Company entered into a grant contract (the “2010 Contract”) with CPRIT, under which the Company received a $10.3 million commercialization award from the State of Texas through CPRIT. CPRIT was established to expedite innovation and commercialization in the area of cancer research and to enhance access to evidence-based prevention programs and services throughout the State of Texas. The award was a three-year award that was funded annually, and the contract terminated on January 31, 2014, subject to the Company's obligations to make certain payments that survive termination. In May 2017, the Company entered into a letter agreement (the “Letter Agreement”) with CPRIT related to the 2010 Contract and the 2014 Contract. In May 2017, Mirna and CPRIT entered into an attachment (the “2010 Amendment”) to amend the 2010 Contract. Pursuant to the Letter Agreement and the 2010 Amendment, in May 2017, Mirna repaid CPRIT $5 million as consideration for the termination of certain grant repayment and other obligations under the 2010 Contract and 2014 Contract. The Company recognized the repayment in research and development expenses within the statement of operations for the three and six month periods ended June 30, 2017.

Net Loss Per Share Attributable to Common Stockholders

6 Months Ended

Jun. 30, 2017

Earnings Per Share [Abstract]

Net Loss Per Share Attributable to Common Stockholders

The following table summarizes the computation of basic and diluted net loss per share attributable to common stockholders of the Company (in thousands, except share and per share data):



	Three Months Ended June 30,						Six Months Ended June 30,
	2017			2016			2017				2016
Net loss attributable to common stockholders—basic and diluted	$	(9,381	)	(5,638		)	$	(14,358	)	—	(12,209		)
Weighted-average number of common shares—basic and diluted	20,856,693			20,831,723			20,853,628				20,831,139
Net loss per share attributable to common stockholders—basic and diluted	$	(0.45	)	$	(0.27	)	$	(0.69	)		$	(0.59	)

As of June 30, 2017 and 2016 the Company has excluded 1,587,874 and 1,905,142 potentially dilutive stock options outstanding, respectively, from the computation of diluted weighted average common shares outstanding, prior to the use of the treasury stock method or if-converted method, because including them would have had an anti-dilutive effect due to the losses reported.

As the Company incurred a net loss for the three and six months ended June 30, 2017 there is no income allocation required under the two‑class method or dilution attributed to weighted‑average shares outstanding in the computation of diluted loss per share attributable to common stockholders.

Summary of Significant Accounting Policies (Policies)

6 Months Ended

Jun. 30, 2017

Accounting Policies [Abstract]

Use of estimates

Research and development costs

Clinical Trial and Pre-Clinical Study Accruals

Stock-based compensation

Stock‑based compensation

Restructuring charges

Fair value measurements


•	Level 1 – Unadjusted prices in active markets for identical assets or liabilities.


•	Level 2 – Quoted prices for similar assets and liabilities in active markets, quoted prices in markets that are not active, or inputs which are observable, either directly or indirectly, for substantially the full term of the asset or liability.


•	Level 3 – Unobservable inputs that reflect the Company’s own assumptions about the assumptions market participants would use in pricing the asset or liability in which there is little, if any, market activity for the asset or liability at the measurement date.

Restricted Cash

Marketable Securities

Recently Adopted Accounting Pronouncements

Marketable Securities (Tables)

6 Months Ended

Jun. 30, 2017

Investments, Debt and Equity Securities [Abstract]

Summary of Available-for-sale Securities Held

The following table summarizes the available-for-sale securities held at June 30, 2017 and December 31, 2016 (in thousands):



	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
June 30, 2017
U.S. government agency securities and treasuries	$	32,519	$	—	$	(17	)	$	32,502
Total available-for-sale securities	$	32,519	$	—	$	(17	)	$	32,502



	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
December 31, 2016
U.S. government agency securities and treasuries	$	42,516	$	4	$	(8	)	$	42,512
Corporate debt securities	1,554		—		—			1,554
Total available-for-sale securities	$	44,070	$	4	$	(8	)	$	44,066

Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2017

Fair Value Disclosures [Abstract]

Schedule of Company's Assets that are Measured at Fair Value on a Recurring Basis

The following table sets forth the Company’s assets that are measured at fair value on a recurring basis as of June 30, 2017 and December 31, 2016 (in thousands):



	Total		Quoted prices in active markets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)
June 30, 2017
Assets:
Cash and cash equivalents
Cash	$	4,061	$	4,061	$	—	$	—
Money market funds	$	11,158	$	11,158	$	—	$	—
Total cash and cash equivalents	15,219		15,219		—		—
Marketable securities
U.S. government agency securities and treasuries	32,502		—		32,502		—
Total fair value financial instruments	$	47,721	$	15,219	$	32,502	$	—



	Total		Quoted prices in active markets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)
December 31, 2016
Assets:
Cash and cash equivalents
Cash	$	2,785	$	2,785	$	—	$	—
Money market funds	$	9,647	$	9,647	$	—	$	—
US government agency securities and treasuries	$	4,000	—		4,000
Total cash and cash equivalents	16,432		12,432		4,000		—
Marketable securities
U.S. government agency securities and treasuries	42,512		—		42,512		—
Corporate debt securities	1,554		—		1,554		—
Total marketable securities	44,066		—		44,066		—
Restricted cash	2,432		2,432		—		—
Total fair value financial instruments	$	62,930	$	14,864	$	48,066	$	—

Property and Equipment (Tables)

6 Months Ended

Jun. 30, 2017

Property, Plant and Equipment [Abstract]

Schedule of Property and Equipment

Property and equipment consisted of the following (in thousands):



	June 30, 2017			December 31, 2016
Furniture, computers and equipment	$	44		$	385
Accumulated depreciation	(31		)	(31		)
	$	13		354

Stock Option Plans (Tables)

6 Months Ended

Jun. 30, 2017

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Schedule of Stock Option Activity

The Company’s stock option activity for the six months ended June 30, 2017 was as follows:



			Weighted‑
			Average		Weighted‑Average
	Number		Exercise		Contractual
	of Shares		Price		Life (years)
Outstanding at December 31, 2016	1,905,214		$	5.39	7.49
Granted	—		—
Exercised	(15,300	)	1.65
Forfeited/canceled	(302,040	)	5.46
Outstanding at June 30, 2017	1,587,874		$	5.41	7.80
Options exercisable at June 30, 2017	1,134,680		$	5.24	7.58

Schedule of Stock Compensation Expense

Total stock-based compensation expense for the three and six months ended June 30, 2017 was recognized as follows in the statements of comprehensive loss (in thousands):



	Three Months Ended June 30,					Six Months Ended June 30,
	2017		2016			2017		2016
Research and development expense	$	30	$	(56	)	$	71	$	115
General and administrative expense	299		298			622		574
Total stock based compensation	$	329	$	242		$	693	$	689

Restructuring Charges (Tables)

6 Months Ended

Jun. 30, 2017

Restructuring and Related Activities [Abstract]

Restructuring Charges

Restructuring charges were as follows (in thousands):



	Three months ended June 30,			Six months ended June 30,
	2017		2016	2017		2016
Employee severance and related costs	$	43	—	$	248	—
Contract termination costs	122		—	2,475		—
Total restructuring charges	$	165	—	$	2,723	—

Schedule of Restructuring Reserve

The accrued restructuring activity for the six months ended June 30, 2017 was as follows (in thousands):



	Employee severance and related costs			Contract Termination Costs			Total
Balance at December 31, 2016	$	1,097		$	1,565		$	2,662
Restructuring charges and adjustments	248			2,475			2,723
Cash payments	(1,234		)	(4,040		)	(5,274		)
Balance at June 30, 2017	$	111		$	—		$	111

Net Loss Per Share Attributable to Common Stockholders (Tables)

6 Months Ended

Jun. 30, 2017

Earnings Per Share [Abstract]

Schedule of Computation of Basic and Diluted Net Loss per Share

The following table summarizes the computation of basic and diluted net loss per share attributable to common stockholders of the Company (in thousands, except share and per share data):



	Three Months Ended June 30,						Six Months Ended June 30,
	2017			2016			2017				2016
Net loss attributable to common stockholders—basic and diluted	$	(9,381	)	(5,638		)	$	(14,358	)	—	(12,209		)
Weighted-average number of common shares—basic and diluted	20,856,693			20,831,723			20,853,628				20,831,139
Net loss per share attributable to common stockholders—basic and diluted	$	(0.45	)	$	(0.27	)	$	(0.69	)		$	(0.59	)

Nature of Business and Basis of Presentation (Details) $ in Millions	Jun. 30, 2017 USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Cash , cash equivalents and marketable securities	$ 47.7

Summary of Significant Accounting Policies (Details)	6 Months Ended
Summary of Significant Accounting Policies (Details)	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($) ft²
Fair value of assets measured at fair value on a recurring basis
Transfers of assets and liabilities between Level 1, Level 2, or Level 3	$ 0	$ 0
Area of lease of office and laboratory space (in sq ft) \| ft²		23,578
Standby Letters of Credit
Fair value of assets measured at fair value on a recurring basis
Standby letter of credit	$ 2,400,000	$ 2,400,000.0

Merger Agreement (Details) $ in Millions	May 16, 2017	May 15, 2017 USD ($) director
Business Acquisition [Line Items]
Number of members on Board of Directors \| director		7
Parent Company
Business Acquisition [Line Items]
Number of members on Board of Directors \| director		2
Synlogic
Business Acquisition [Line Items]
Number of members on Board of Directors \| director		5
Merger Agreement
Business Acquisition [Line Items]
Minimum net cash threshold		$ 33.5
Merger agreement termination fee		2.0
Maximum expense reimbursement required subsequent to termination		$ 1.0
Merger Agreement \| Stock subject to lock up agreement
Business Acquisition [Line Items]
Restrictions on share transfer following merger, term		180 days
Merger Agreement \| Parent Company
Business Acquisition [Line Items]
Net cash at closing		$ 40.0
Shares outstanding, percent in support of Merger Agreement		33.00%
Merger Agreement \| Parent Company \| Stock subject to lock up agreement
Business Acquisition [Line Items]
Shares outstanding, percent in support of Merger Agreement		33.00%
Merger Agreement \| Synlogic
Business Acquisition [Line Items]
Shares outstanding, percent in support of Merger Agreement		77.00%
Merger Agreement \| Synlogic \| Stock subject to lock up agreement
Business Acquisition [Line Items]
Shares outstanding, percent in support of Merger Agreement		81.00%
Merger Agreement \| Mirna outstanding common stock \| Parent Company
Business Acquisition [Line Items]
Share ownership prior to merger, percent		17.00%
Merger Agreement \| Mirna outstanding common stock \| Synlogic
Business Acquisition [Line Items]
Share ownership following merger, percent	83.00%

Marketable Securities (Details) - USD ($)	Jun. 30, 2017	Dec. 31, 2016
Available-for-sale securities held
Amortized Cost	$ 32,519,000	$ 44,070,000
Unrealized Gains	0	4,000
Unrealized Losses	(17,000)	(8,000)
Fair Value	32,502,000	44,066,000
Maturities
Available-for-sale securities with remaining maturities greater than one year	0
U.S. government agency securities and treasuries
Available-for-sale securities held
Amortized Cost	32,519,000	42,516,000
Unrealized Gains	0	4,000
Unrealized Losses	(17,000)	(8,000)
Fair Value	$ 32,502,000	42,512,000
Corporate debt securities
Available-for-sale securities held
Amortized Cost		1,554,000
Unrealized Gains		0
Unrealized Losses		0
Fair Value		$ 1,554,000

Fair Value Measurements (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Fair value of assets measured at fair value on a recurring basis
Marketable securities	$ 32,502	$ 44,066
Marketable securities
Available for sale securities in an unrealized loss position	32,500
Available for sale securities, unrealized loss	17
Recurring
Fair value of assets measured at fair value on a recurring basis
Marketable securities		44,066
Total fair value financial instruments	47,721	62,930
Recurring \| U.S. government agency securities and treasuries
Fair value of assets measured at fair value on a recurring basis
Marketable securities	32,502	42,512
Recurring \| Corporate debt securities
Fair value of assets measured at fair value on a recurring basis
Marketable securities		1,554
Recurring \| Cash
Fair value of assets measured at fair value on a recurring basis
Cash and cash equivalents	4,061	2,785
Recurring \| Money market funds
Fair value of assets measured at fair value on a recurring basis
Cash and cash equivalents	11,158	9,647
Recurring \| U.S. government agency securities and treasuries
Fair value of assets measured at fair value on a recurring basis
Cash and cash equivalents		4,000
Recurring \| Total cash and cash equivalents
Fair value of assets measured at fair value on a recurring basis
Cash and cash equivalents	15,219	16,432
Recurring \| Restricted cash
Fair value of assets measured at fair value on a recurring basis
Cash and cash equivalents		2,432
Recurring \| Quoted prices in active markets (Level 1)
Fair value of assets measured at fair value on a recurring basis
Marketable securities		0
Total fair value financial instruments	15,219	14,864
Recurring \| Quoted prices in active markets (Level 1) \| U.S. government agency securities and treasuries
Fair value of assets measured at fair value on a recurring basis
Marketable securities	0	0
Recurring \| Quoted prices in active markets (Level 1) \| Corporate debt securities
Fair value of assets measured at fair value on a recurring basis
Marketable securities		0
Recurring \| Quoted prices in active markets (Level 1) \| Cash
Fair value of assets measured at fair value on a recurring basis
Cash and cash equivalents	4,061	2,785
Recurring \| Quoted prices in active markets (Level 1) \| Money market funds
Fair value of assets measured at fair value on a recurring basis
Cash and cash equivalents	11,158	9,647
Recurring \| Quoted prices in active markets (Level 1) \| U.S. government agency securities and treasuries
Fair value of assets measured at fair value on a recurring basis
Cash and cash equivalents		0
Recurring \| Quoted prices in active markets (Level 1) \| Total cash and cash equivalents
Fair value of assets measured at fair value on a recurring basis
Cash and cash equivalents	15,219	12,432
Recurring \| Quoted prices in active markets (Level 1) \| Restricted cash
Fair value of assets measured at fair value on a recurring basis
Cash and cash equivalents		2,432
Recurring \| Significant other observable inputs (Level 2)
Fair value of assets measured at fair value on a recurring basis
Marketable securities		44,066
Total fair value financial instruments	32,502	48,066
Recurring \| Significant other observable inputs (Level 2) \| U.S. government agency securities and treasuries
Fair value of assets measured at fair value on a recurring basis
Marketable securities	32,502	42,512
Recurring \| Significant other observable inputs (Level 2) \| Corporate debt securities
Fair value of assets measured at fair value on a recurring basis
Marketable securities		1,554
Recurring \| Significant other observable inputs (Level 2) \| Cash
Fair value of assets measured at fair value on a recurring basis
Cash and cash equivalents	0	0
Recurring \| Significant other observable inputs (Level 2) \| Money market funds
Fair value of assets measured at fair value on a recurring basis
Cash and cash equivalents	0	0
Recurring \| Significant other observable inputs (Level 2) \| U.S. government agency securities and treasuries
Fair value of assets measured at fair value on a recurring basis
Cash and cash equivalents		4,000
Recurring \| Significant other observable inputs (Level 2) \| Total cash and cash equivalents
Fair value of assets measured at fair value on a recurring basis
Cash and cash equivalents	0	4,000
Recurring \| Significant other observable inputs (Level 2) \| Restricted cash
Fair value of assets measured at fair value on a recurring basis
Cash and cash equivalents		0
Recurring \| Significant unobservable inputs (Level 3)
Fair value of assets measured at fair value on a recurring basis
Marketable securities		0
Total fair value financial instruments	0	0
Recurring \| Significant unobservable inputs (Level 3) \| U.S. government agency securities and treasuries
Fair value of assets measured at fair value on a recurring basis
Marketable securities	0	0
Recurring \| Significant unobservable inputs (Level 3) \| Corporate debt securities
Fair value of assets measured at fair value on a recurring basis
Marketable securities		0
Recurring \| Significant unobservable inputs (Level 3) \| Cash
Fair value of assets measured at fair value on a recurring basis
Cash and cash equivalents	0	0
Recurring \| Significant unobservable inputs (Level 3) \| Money market funds
Fair value of assets measured at fair value on a recurring basis
Cash and cash equivalents	0	0
Recurring \| Significant unobservable inputs (Level 3) \| U.S. government agency securities and treasuries
Fair value of assets measured at fair value on a recurring basis
Cash and cash equivalents
Recurring \| Significant unobservable inputs (Level 3) \| Total cash and cash equivalents
Fair value of assets measured at fair value on a recurring basis
Cash and cash equivalents	$ 0	0
Recurring \| Significant unobservable inputs (Level 3) \| Restricted cash
Fair value of assets measured at fair value on a recurring basis
Cash and cash equivalents		$ 0

Property and Equipment (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
Property and Equipment (Details) - USD ($) $ in Thousands	Feb. 28, 2017	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Furniture, computers and equipment		$ 44		$ 44		$ 385
Accumulated depreciation		(31)		(31)		(31)
Property and equipment, net		13		13		$ 354
Depreciation expense		$ 13	$ 26	18	$ 45
Cash consideration for sale of lab equipment				$ 325	$ 0
Lab Equipment
Property, Plant and Equipment [Line Items]
Cash consideration for sale of lab equipment	$ 325

Common Stock - Voting and Dividends (Details)	6 Months Ended	112 Months Ended
Common Stock - Voting and Dividends (Details)	Jun. 30, 2017 vote	Mar. 31, 2017 USD ($)
Stockholders' Equity Note [Abstract]
Number of votes per common stock \| vote	1
Cash dividends \| $		$ 0

Common Stock - Offerings (Details) - USD ($) $ / shares in Units, $ in Millions		1 Months Ended
	Oct. 05, 2015	Oct. 31, 2015	Sep. 30, 2015
Common Stock \| Initial Public Offering
Class of Stock [Line Items]
Shares issued (in shares)		6,250,000
Share price (in USD per share)		$ 7.00
Proceeds from issuance of common stock in initial public offering		$ 43.7
Common Stock \| Over-Allotment Option
Class of Stock [Line Items]
Shares issued (in shares)		704,962
CPRIT
Class of Stock [Line Items]
Grant contract			$ 16.8
Purchase agreement			$ 16.8
CPRIT \| Common Stock \| Private Placement
Class of Stock [Line Items]
Shares issued (in shares)	2,395,010
Share price (in USD per share)	$ 7.00
Proceeds from issuance of common stock in private placement	$ 16.6

Stock Option Plans - Plan Information (Details) - $ / shares	1 Months Ended			3 Months Ended		6 Months Ended	12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2017	Mar. 31, 2016	Jun. 30, 2017	Dec. 31, 2016	Aug. 31, 2015	Dec. 31, 2008
Number of Shares
Outstanding at beginning of period (in shares)				1,905,214		1,905,214
Granted (in shares)						0
Exercised (in shares)						(15,300)
Forfeited/canceled (in shares)						(302,040)
Outstanding at end of period (in shares)						1,587,874	1,905,214
Exercisable at end of period (in shares)						1,134,680
Weighted Average Exercise Price
Outstanding at beginning of period (in USD per share)				$ 5.39		$ 5.39
Granted (in USD per share)						0.00
Exercised (in USD per share)						1.65
Forfeited/canceled (in USD per share)						5.46
Outstanding at end of period (in USD per share)						5.41	$ 5.39
Exercisable at end of period (in USD per share)						$ 5.24
Additional disclosures
Weighted Average Remaining Contractual Life, Options outstanding						7 years 9 months 18 days	7 years 5 months 27 days
Weighted Average Remaining Contractual Life, Options exercisable						7 years 6 months 29 days
ESPP
Stock Option Plans
Number of stock options and stock purchase rights available for grant (in shares)						369,960
Percentage of discount for employees under ESPP						15.00%
Purchase price as a percentage of fair value under ESPP						85.00%
2008 Plan
Stock Option Plans
Number of stock options and stock purchase rights available for grant (in shares)	1,061,585	669,935	554,782						330,582
Increase in number of stock options and stock purchase rights available for grant (in shares)	391,650	115,153	224,200
Expiration period						10 years
Shares transferred from the 2008 long term incentive plan to the 2015 equity incentive plan (in shares)						333,100
Number of Shares
Outstanding at end of period (in shares)						446,765
2015 Plan
Stock Option Plans
Number of stock options and stock purchase rights available for grant (in shares)								1,671,800
Increase in number of stock options and stock purchase rights available for grant (in shares)				1,042,070	1,041,527
2008 Plan and 2015 Plan
Stock Option Plans
Number of stock options and stock purchase rights available for grant (in shares)						4,088,497

Stock Option Plans - Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Stock-based compensation expense allocation
Stock based compensation	$ 329	$ 242	$ 693	$ 689
Stock Appreciation Rights
Stock-based compensation expense allocation
Awards granted (in shares)			0
2015 Plan \| Stock Options
Stock-based compensation expense allocation
Unrecognized compensation cost	1,700		$ 1,700
Unrecognized compensation cost, period of recognition			2 years 22 days
2015 Plan \| Restricted Stock Units
Stock-based compensation expense allocation
Awards granted (in shares)			0
Research and development expense
Stock-based compensation expense allocation
Stock based compensation	30	(56)	$ 71	115
General and administrative expense
Stock-based compensation expense allocation
Stock based compensation	$ 299	$ 298	$ 622	$ 574

Income Taxes (Details) - USD ($)	6 Months Ended
Income Taxes (Details) - USD ($)	Jun. 30, 2017	Jun. 30, 2016
Income Tax Disclosure [Abstract]
Interest and penalties related to income taxes	$ 0	$ 0

Restructuring Charges - Narrative (Details) $ in Thousands	1 Months Ended		3 Months Ended			6 Months Ended		9 Months Ended	12 Months Ended
Restructuring Charges - Narrative (Details) $ in Thousands	May 31, 2017 USD ($)	Feb. 28, 2017 USD ($)	Jun. 30, 2017 USD ($) employee	Dec. 31, 2016 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) employee	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) employee	Dec. 31, 2016 USD ($)	Sep. 28, 2016 employee	Sep. 27, 2016 employee
Restructuring Cost and Reserve [Line Items]
Number of employees \| employee			4			4		4		12	36
Restructuring expense				$ 4,400		$ 2,723		$ 7,200
Non-cash impairment charges				1,400					$ 1,400
Employee severance and related costs			$ 43		$ 0	248	$ 0
Contract termination costs			122		0	2,475	0		1,500
Total restructuring charges			165		$ 0	2,723	0
Accrued restructuring			111	2,662		111		111	2,662
Consideration paid for settlement of lease	$ 3,800
Cash consideration for sale of lab equipment						325	$ 0
Lab Equipment
Restructuring Cost and Reserve [Line Items]
Non-cash impairment charges									555
Cash consideration for sale of lab equipment		$ 325
Construction in Progress
Restructuring Cost and Reserve [Line Items]
Non-cash impairment charges									591
Furniture, Computers, Equipment, and Leasehold Improvements
Restructuring Cost and Reserve [Line Items]
Non-cash impairment charges									256
Contract Termination Costs
Restructuring Cost and Reserve [Line Items]
Restructuring expense						2,475
Accrued restructuring			$ 0	$ 1,565		$ 0		$ 0	$ 1,565

Restructuring Charges - Accumulated Restructuring Charges (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended	9 Months Ended
	Dec. 31, 2016	Jun. 30, 2017	Jun. 30, 2017
Restructuring Cost and Reserve [Line Items]
Balance at December 31, 2016		$ 2,662
Restructuring charges and adjustments	$ 4,400	2,723	$ 7,200
Cash payments		(5,274)
Balance at June 30, 2017	2,662	111	111
Employee severance and related costs
Restructuring Cost and Reserve [Line Items]
Balance at December 31, 2016		1,097
Restructuring charges and adjustments		248
Cash payments		(1,234)
Balance at June 30, 2017	1,097	111	111
Contract Termination Costs
Restructuring Cost and Reserve [Line Items]
Balance at December 31, 2016		1,565
Restructuring charges and adjustments		2,475
Cash payments		(4,040)
Balance at June 30, 2017	$ 1,565	$ 0	$ 0

Commitments and Contingencies (Detail)	1 Months Ended		6 Months Ended
Commitments and Contingencies (Detail)	May 31, 2017 USD ($)	Aug. 31, 2010 USD ($)	Jun. 30, 2017 USD ($) draw term	Jun. 30, 2016 USD ($)
Shared Services Agreement
Initial term of lease			123 months
Number of terms lease can be extended \| term			2
Renewal term option of lease			60 months
Annual base rent			$ 600,000
Rent free term			3 months
Yearly increases in base rent			3.00%
Tenant improvement allowance			$ 1,900,000
Number of draws taken on the additional improvement allowance \| draw			0
Commercialization award received		$ 10,300,000
Commercialization award term		3 years
Payment for termination of grant repayment and other obligations	$ 5,000,000
Standby Letters of Credit
Shared Services Agreement
Initial amount of standby letter of credit			$ 2,400,000	$ 2,400,000.0

Net Loss Per Share Attributable to Common Stockholders - Computation (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Earnings Per Share [Abstract]
Net loss attributable to common stockholders—basic and diluted	$ (9,381)	$ (5,638)	$ (14,358)	$ (12,209)
Weighted-average number of common shares—basic and diluted (in shares)	20,856,693	20,831,723	20,853,628	20,831,139
Net loss per share attributable to common stockholders—basic and diluted (in USD per share)	$ (0.45)	$ (0.27)	$ (0.69)	$ (0.59)

Net Loss Per Share Attributable to Common Stockholders - Dilutive Securities (Details) - shares	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Earnings Per Share [Abstract]
Potentially dilutive securities excluded from the computation of diluted weighted average common shares outstanding	1,587,874	1,905,142