Regulus Therapeutics (RGLS) 10-Q 8 Nov 17 2017 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2017	Nov. 03, 2017
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	Q3
Trading Symbol	RGLS
Entity Registrant Name	REGULUS THERAPEUTICS INC.
Entity Central Index Key	1,505,512
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		103,955,147

Condensed Balance Sheets

Condensed Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 20,222	$ 14,941
Short-term investments	51,148	61,170
Contract and other receivables	532	1,657
Prepaid materials, net	5,912	5,552
Prepaid expenses and other current assets	1,752	4,154
Total current assets	79,566	87,474
Property and equipment, net	10,172	11,830
Intangibles, net	802	1,015
Other assets	307	342
Total assets	90,847	100,661
Current liabilities:
Accounts payable	5,229	5,840
Accrued liabilities	4,770	5,577
Accrued compensation	1,687	2,318
Current portion of deferred revenue	72	72
Total current liabilities	11,758	13,807
Term loan, less debt issuance costs	19,845	19,802
Deferred revenue, less current portion	1,939	1,993
Deferred rent, less current portion	8,372	8,840
Other long-term liabilities	351	144
Total liabilities	42,265	44,586
Commitments and Contingencies
Stockholders’ equity:
Common stock, $0.001 par value; 200,000,000 shares authorized, 103,955,147 and 52,924,805 shares issued and outstanding at September 30, 2017 (unaudited) and December 31, 2016, respectively	104	53
Additional paid-in capital	379,992	329,496
Accumulated other comprehensive loss	(104)	(123)
Accumulated deficit	(331,410)	(273,351)
Total stockholders’ equity	48,582	56,075
Total liabilities and stockholders’ equity	$ 90,847	$ 100,661

Condensed Balance Sheets (Paren

Condensed Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	103,955,147	52,924,805
Common stock, shares outstanding	103,955,147	52,924,805

Condensed Statements of Operati

Condensed Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Revenues:
Total revenues	$ 18	$ 204	$ 54	$ 1,176
Operating expenses:
Research and development	12,697	14,554	42,727	49,326
General and administrative	2,736	4,842	13,752	13,609
Total operating expenses	15,433	19,396	56,479	62,935
Loss from operations	(15,415)	(19,192)	(56,425)	(61,759)
Other income (expense):
Interest and other income	160	237	559	608
Interest and other expense	(580)	(560)	(1,730)	(674)
Loss before income taxes	(15,835)	(19,515)	(57,596)	(61,825)
Income tax benefit (expense)	7	(4)	139	9
Net loss	(15,828)	(19,519)	(57,457)	(61,816)
Other comprehensive loss:
Unrealized (loss) gain on short-term investments, net	(16)	(30)	19	20
Comprehensive loss	$ (15,844)	$ (19,549)	$ (57,438)	$ (61,796)
Net loss per share, basic and diluted (in dollars per share)	$ (0.18)	$ (0.37)	$ (0.88)	$ (1.17)
Weighted average shares used to compute basic and diluted net loss per share (in shares)	90,072,045	52,835,414	65,550,749	52,776,459
Strategic Alliances and Collaborations
Revenues:
Total revenues	$ 18	$ 204	$ 54	$ 1,176

Condensed Statements of Cash Fl

Condensed Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Operating activities
Net loss	$ (57,457)	$ (61,816)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and amortization expense	1,942	1,589
Stock-based compensation	6,531	9,453
Amortization of premium on investments, net	271	525
Other	206	338
Change in operating assets and liabilities:
Contracts and other receivables	1,124	9,735
Prepaid materials	(360)	(1,329)
Prepaid expenses and other assets	2,405	(634)
Accounts payable	(579)	3,007
Accrued liabilities	(652)	(1,187)
Accrued compensation	(631)	(102)
Deferred revenue	(54)	(1,176)
Deferred rent and other liabilities	(418)	(178)
Net cash used in operating activities	(47,672)	(41,775)
Investing activities
Purchases of short-term investments	(48,539)	(60,716)
Sales and maturities of short-term investments	58,310	81,437
Purchases of property and equipment	(217)	(746)
Acquisition of intangibles	(16)	(48)
Net cash provided by investing activities	9,538	19,927
Financing activities
Proceeds from borrowing under term loan, net	0	19,768
Proceeds from issuance of common stock, net	43,411	641
Proceeds from exercise of common stock options	4	309
Principal payments on other long-term obligations	0	(124)
Net cash provided by financing activities	43,415	20,594
Net increase (decrease) in cash and cash equivalents	5,281	(1,254)
Cash and cash equivalents at beginning of period	14,941	15,960
Cash and cash equivalents at end of period	20,222	14,706
Supplemental disclosure of cash flow information
Net changes in restricted cash	0	(1,176)
Interest paid	(1,444)	(518)
Income taxes paid	(1)	(1)
Supplemental disclosure of non-cash investing and financing activities
Allowance for tenant improvements	0	6,653
Amounts accrued for property and equipment	0	14
Amounts accrued for patent expenditures	$ 0	$ 5

Basis of Presentation and Summa

Basis of Presentation and Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2017
Accounting Policies [Abstract]
Basis of Presentation and Summary of Significant Accounting Policies	Basis of Presentation and Summary of Significant Accounting Policies Basis of Presentation The accompanying unaudited condensed financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”) for interim financial information and the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. In management’s opinion, the accompanying financial statements reflect all adjustments, consisting of normal recurring adjustments, considered necessary for a fair presentation of the results for the interim periods presented. Interim financial results are not necessarily indicative of results anticipated for the full year. These unaudited condensed financial statements should be read in conjunction with the audited financial statements and footnotes included in our Annual Report on Form 10-K for the year ended December 31, 2016 , from which the balance sheet information herein was derived. We have incurred losses in each year since our inception. We expect to continue to incur significant expenses and operating losses for the foreseeable future in connection with our research and preclinical and clinical development of our product candidates. In order to continue to fund our research and development activities, we will need to seek additional capital. This may occur through strategic alliance and licensing arrangements and/or future public or private debt or equity financings. Sufficient funding may not be available, or if available, may be on terms that significantly dilute or otherwise adversely affect the rights of existing stockholders. If adequate funds are not available in the future, we may need to delay, reduce the scope of or put on hold one or more or our clinical and/or preclinical programs while we seek strategic alternatives. In May 2017, we implemented a corporate restructuring to streamline our operations, reduce our operating expenses, extend our cash runway and focus our resources on our most promising programs. In connection with the restructuring, we committed to a reduction in our total workforce by approximately 30% percent, to approximately 65 employees. We completed the workforce reduction in June 2017. We recorded charges of approximately $3.2 million for employee severance and other related termination benefits in the second quarter of 2017, including $1.3 million in net adjustments to non-cash stock-based compensation. All payments associated with the corporate restructuring were paid in full as of June 30, 2017. As of September 30, 2017, we had cash, cash equivalents and short-term investments of $71.4 million under Financial Accounting Standards Board, or FASB, Accounting Standards Update, or ASU, 2014-15, Presentation of Financial Statements - Going Concern . We have evaluated and concluded that there are no conditions or events, considered individually or in the aggregate, that raise substantial doubt about our ability to continue as a going concern for a period of one year following the date that these financial statements are issued. Use of Estimates Our condensed financial statements are prepared in accordance with GAAP, which requires us to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses and the disclosure of contingent assets and liabilities in our financial statements and accompanying notes. An estimated loss contingency is accrued in our financial statements if it is probable that a liability has been incurred and the amount of the loss can be reasonably estimated. Although these estimates are based on our knowledge of current events and actions we may undertake in the future, actual results may ultimately differ from these estimates and assumptions. Revenue Recognition Our revenues generally consist of upfront payments for licenses or options to obtain licenses in the future, milestone payments and payments for other research services under strategic alliance and collaboration agreements. We recognize revenues when all four of the following criteria are met: (1) persuasive evidence of an arrangement exists; (2) delivery of the products and/or services has occurred; (3) the selling price is fixed or determinable; and (4) collectability is reasonably assured. Multiple element arrangements, such as our strategic alliance agreement with Sanofi, are analyzed to determine whether the deliverables within the agreement can be separated or whether they must be accounted for as a single unit of accounting. Deliverables under the agreement will be accounted for as separate units of accounting provided that (i) a delivered item has value to the customer on a stand-alone basis; and (ii) if the agreement includes a general right of return relative to the delivered item, delivery or performance of the undelivered item is considered probable and substantially in the control of the vendor. The allocation of consideration amongst the deliverables under the agreement is derived using a “best estimate of selling price” if vendor specific objective evidence and third-party evidence of fair value is not available. If the delivered element does not have stand-alone value, the arrangement is then accounted for as a single unit of accounting, and we recognize the consideration received under the arrangement as revenue on a straight-line basis, which approximates effort over our estimated period of performance, which for us is typically the expected term of the research and development plan. Milestones We apply the milestone method of accounting to recognize revenue from milestone payments when earned, as evidenced by written acknowledgment from the collaborator or other persuasive evidence that the milestone has been achieved and the payment is non-refundable, provided that the milestone event is substantive. A milestone event is defined as an event (i) that can only be achieved based in whole or in part on either our performance or on the occurrence of a specific outcome resulting from our performance; (ii) for which there is substantive uncertainty at the inception of the arrangement that the event will be achieved; and (iii) that would result in additional payments being due to us. Events for which the occurrence is either contingent solely upon the passage of time or the result of a counterparty’s performance are not considered to be milestone events. A milestone event is substantive if all of the following conditions are met: (i) the consideration is commensurate with either our performance to achieve the milestone, or the enhancement of the value to the delivered item(s) as a result of a specific outcome resulting from our performance to achieve the milestone; (ii) the consideration relates solely to past performance; and (iii) the consideration is reasonable relative to all the deliverables and payment terms (including other potential milestone consideration) within the arrangement. We assess whether a milestone is substantive at the inception of each arrangement. If a milestone is deemed non-substantive, we will account for that milestone payment using a method consistent with the related units of accounting for the arrangement over the estimated performance period. Deferred Revenue Amounts received prior to satisfying the above revenue recognition criteria are recorded as deferred revenue in the accompanying balance sheets. Amounts not expected to be recognized within the next 12 months are classified as non-current deferred revenue. Stock-Based Compensation We account for stock-based compensation expense related to stock options granted to employees and members of our board of directors by estimating the fair value of each stock option on the date of grant using the Black-Scholes option pricing model. We recognize stock-based compensation expense using the accelerated multiple-option approach. Under the accelerated multiple-option approach (also known as the graded-vesting method), we recognize compensation expense over the requisite service period for each separately vesting tranche of the award as though the award was in substance multiple awards, resulting in accelerated expense recognition over the vesting period. For performance-based awards granted to employees (i) the fair value of the award is determined on the grant date, (ii) we assess the probability of the individual milestones under the award being achieved and (iii) the fair value of the shares subject to the milestone is expensed over the implicit service period commencing once management believes the performance criteria is probable of being met. We account for stock options granted to non-employees using the fair value approach. Stock options granted to non-employees are subject to periodic revaluation over their vesting terms. Clinical Trial and Preclinical Study Accruals We make estimates of our accrued expenses for clinical trial and preclinical study activities as of each balance sheet date in our financial statements based on the facts and circumstances known to us at that time. These accruals are based upon estimates of costs incurred and fees that may be associated with services provided by clinical trial investigational sites, clinical research organizations (“CROs”) and for other clinical trial-related activities. Payments under certain contracts with such parties depend on factors such as successful enrollment of patients, site initiation and the completion of clinical trial milestones. In accruing for these services, we estimate the time period over which services will be performed and the level of effort to be expended in each period. If possible, we obtain information regarding unbilled services directly from these service providers. However, we may be required to estimate these services based on other information available to us. If we underestimate or overestimate the activities or fees associated with a study or service at a given point in time, adjustments to research and development expenses may be necessary in future periods. Historically, our estimated accrued liabilities have approximated actual expense incurred. Subsequent changes in estimates may result in a material change in our accruals. Prepaid Materials We capitalize the purchase of certain raw materials and related supplies for use in the manufacturing of drug product in our clinical development programs, as we have determined that these materials have alternative future use. We can use these raw materials and related supplies in multiple clinical drug products, and therefore have future use independent of the development status of any particular drug program until it is utilized in the manufacturing process. We expense the cost of materials when used. We periodically review these capitalized materials for continued alternative future use and write down the asset to its net realizable value in the period in which it is identified. As of September 30, 2017 and December 31, 2016 , our net prepaid materials balance was $5.9 million and $5.6 million , respectively. Recent Accounting Pronouncements In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606) , which outlines a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance, including industry-specific guidance. ASU 2014-09 outlines a five-step process for revenue recognition that focuses on transfer of control, as opposed to transfer of risk and rewards, and also requires enhanced disclosures regarding the nature, amount, timing and uncertainty of revenues and cash flows from contracts with customers. Major provisions include determining which goods and services are distinct and require separate accounting (performance obligations), how variable consideration (which may include change orders and claims) is recognized, whether revenue should be recognized at a point in time or over time and ensuring the time value of money is considered in the transaction price. The FASB issued supplemental adoption guidance and clarification to ASU No. 2014-09 in March 2016, April 2016 and May 2016 within ASU No. 2016-08, Revenue from Contracts with Customers: Principal vs. Agent Considerations , ASU No. 2016-10, Revenue from Contracts with Customers: Identifying Performance Obligations and Licensing and ASU No. 2016-12, Revenue from Contracts with Customers: Narrow-Scope Improvements and Practical Expedients , respectively. ASU No. 2014-09 and the related supplemental ASUs are effective for fiscal years beginning after December 15, 2017 and interim periods therein. The ASU permits two methods of adoption: the full retrospective method or the modified retrospective method. We plan to apply the modified retrospective method upon adoption in the first quarter of 2018 and currently do not anticipate that the adoption of this ASU will have a material impact with regard to our current contracts. In January 2016, the FASB issued ASU No. 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities , which eliminates the requirement for public companies to disclose the method(s) and significant assumptions used to estimate the fair value for financial instruments measured at amortized cost on the balance sheet. Additionally, the standard requires public companies to use the exit price notion when measuring the fair value of financial instruments for disclosure purposes. Furthermore, the standard requires presentation of financial assets and liabilities by measurement category and form of financial asset on the balance sheet or accompanying notes to the financial statements. The standard is effective for annual reporting periods beginning after December 15, 2017, including interim periods within those annual reporting periods. Early application is permitted. The adoption of this guidance will have no impact on our financial statements. In February 2016, the FASB issued ASU No. 2016-02, Leases, which increases transparency and comparability among organizations by requiring recognition of lease assets and lease liabilities on the balance sheet and disclosure of key information about leasing arrangements. The standard is effective for annual reporting periods beginning after December 15, 2018, including interim periods within those annual reporting periods. Early application is permitted. We are currently evaluating the impact of adoption on our financial statements. In March 2016, the FASB issued ASU No. 2016-09, Compensation – Stock Compensation: Improvements to Employee Share-Based Payment Accounting, which was intended to simplify various aspects of accounting for share-based payment transactions. The new guidance requires immediate recognition of all excess tax benefits and deficiencies in the income statement, requires classification of excess tax benefits as an operating activity as opposed to a financing activity in the statements of cash flows and allows the Company to make an accounting policy election to either estimate the number of awards expected to vest or account for forfeitures when they occur. The standard is effective for annual reporting periods beginning after December 15, 2016, and interim periods within those annual reporting periods. We applied this standard in the first quarter of 2017 using the modified retrospective method of adoption. In conjunction with this adoption, we made an accounting policy election to account for forfeitures as they occur. Upon adoption, we reversed a deferred tax asset related to the balance of unrecognized excess tax benefits of $7.4 million , with an offsetting adjustment to the valuation allowance. Under the modified retrospective method of adoption, we recorded an adjustment of $0.6 million to accumulated deficit with a corresponding offset to additional paid-in capital. In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows: Classification of Certain Cash Receipts and Cash Payments , which addresses the presentation and classification of certain cash receipts and cash payments in the statement of cash flows under Accounting Standards Codification 230. The standard is effective for annual reporting periods beginning after December 15, 2017, and interim periods within those annual reporting periods. The adoption of this guidance will have no impact on our financial statements. In November 2016, the FASB issued ASU No. 2016-18, Statement of Cash Flows: Restricted Cash , which requires restricted cash and restricted cash equivalents to be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. The standard is effective for annual reporting periods beginning after December 15, 2017, and interim periods within those annual reporting periods. Early application is permitted. Upon its adoption in 2018, we will include $1.3 million of restricted cash in our disclosed balance of cash and cash equivalents at the beginning of the period for 2016. We do not expect any additional impact on our financial statements. In May 2017, the FASB issued ASU No. 2017-09, Compensation - Stock Compensation: Scope of Modification Accounting , which provides clarity and guidance around which changes to the terms or conditions of a share-based payment award require an entity to apply modification accounting in Topic 718. The standard is effective for annual reporting periods beginning after December 15, 2017, and interim periods within those annual reporting periods. The adoption of this guidance will have no impact on our financial statements unless we have modification accounting in accordance with Topic 718.

Net Loss Per Share

Net Loss Per Share	9 Months Ended
	Sep. 30, 2017
Earnings Per Share [Abstract]
Net Loss Per Share	Net Loss Per Share Basic net loss per share is calculated by dividing net loss by the weighted average number of common shares outstanding for the period, without consideration for common stock equivalents. Diluted net loss per share is calculated by dividing net loss by the weighted-average number of common share equivalents outstanding for the period determined using the treasury-stock method. Dilutive common stock equivalents are comprised of options outstanding under our stock option plans. For all periods presented, there is no difference in the number of shares used to calculate basic and diluted net loss per share. Potentially dilutive securities not included in the calculation of diluted net loss per share because to do so would be anti-dilutive consisted of 1,281,022 and 2,531,362 shares attributable to common stock options for the three and nine months ended September 30, 2017 , respectively, compared to 3,131,911 and 3,762,952 shares attributable to common stock options for the same periods in 2016.

Investments

Investments	9 Months Ended
	Sep. 30, 2017
Investments, Debt and Equity Securities [Abstract]
Investments	Investments We invest our excess cash primarily in commercial paper and debt instruments of financial institutions, corporations, U.S. government-sponsored agencies and the U.S. Treasury. As of September 30, 2017 , our short-term investments had a weighted average maturity of less than two years. The following tables summarize our short-term investments (in thousands): Maturity (in years) Amortized cost Unrealized Estimated fair value Gains Losses As of September 30, 2017 Corporate debt securities 1 or less $ 38,736 $ 1 $ (30 ) $ 38,707 Certificates of deposit 2 or less 6,450 — — 6,450 U.S. Treasury securities 2 or less 4,502 — (6 ) 4,496 Debt securities of U.S. government-sponsored agencies 1 or less 1,497 — (2 ) 1,495 Total $ 51,185 $ 1 $ (38 ) $ 51,148 Maturity (in years) Amortized cost Unrealized Estimated fair value Gains Losses As of December 31, 2016 Corporate debt securities 2 or less $ 49,185 $ 12 $ (77 ) $ 49,120 Certificates of deposit 1 or less 9,291 — — 9,291 Commercial paper 1 or less 1,247 — — 1,247 U.S. Treasury securities 1 or less 1,001 — (1 ) 1,000 Debt securities of U.S. government-sponsored agencies 1 or less 512 — — 512 Total $ 61,236 $ 12 $ (78 ) $ 61,170

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements We have certain financial assets recorded at fair value which have been classified as Level 1, 2, or 3 within the fair value hierarchy as described in the accounting standards for fair value measurements. Accounting standards define fair value as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants as of the measurement date. Market participants are buyers and sellers in the principal market that are (i) independent, (ii) knowledgeable, (iii) able to transact, and (iv) willing to transact. The accounting standards provide an established hierarchy for inputs used in measuring fair value that maximizes the use of observable inputs and minimizes the use of unobservable inputs by requiring that the most observable inputs be used when available. Observable inputs are inputs that market participants would use in valuing the asset or liability and are developed based on market data obtained from independent sources. Unobservable inputs are inputs that reflect our assumptions about the factors that market participants would use in valuing the asset or liability. The accounting standards prioritize the inputs used in measuring the fair value into the following hierarchy: • Level 1 includes financial instruments for which quoted market prices for identical instruments are available in active markets. • Level 2 includes financial instruments for which there are inputs other than quoted prices included within Level 1 that are observable for the instrument such as quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets with insufficient volume or infrequent transactions (less active markets) or model-driven valuations in which significant inputs are observable or can be derived principally from, or corroborated by, observable market data. • Level 3 includes financial instruments for which fair value is derived from valuation techniques in which one or more significant inputs are unobservable, including management’s own assumptions. Financial Assets Measured at Fair Value The following table presents our fair value hierarchy for assets measured at fair value on a recurring basis as of September 30, 2017 and December 31, 2016 (in thousands): Fair value as of September 30, 2017 Total Level 1 Level 2 Level 3 Assets: Cash equivalents $ 18,078 $ 18,078 $ — $ — Corporate debt securities 38,707 — 38,707 — Certificates of deposit 6,450 — 6,450 — U.S. treasury securities 4,496 — 4,496 — Debt securities of U.S. government-sponsored agencies 1,495 — 1,495 — $ 69,226 $ 18,078 $ 51,148 $ — Fair value as of December 31, 2016 Total Level 1 Level 2 Level 3 Assets: Cash equivalents $ 13,578 $ 13,578 $ — $ — Corporate debt securities 49,120 — 49,120 — Certificates of deposit 9,291 — 9,291 — Commercial paper 1,247 — 1,247 — U.S. treasury securities 1,000 — 1,000 — Debt securities of U.S. government-sponsored agencies 512 — 512 — $ 74,748 $ 13,578 $ 61,170 $ — We obtain pricing information from quoted market prices or quotes from brokers/dealers. We generally determine the fair value of our investment securities using standard observable inputs, including reported trades, broker/dealer quotes, bids and/or offers. Refer to Note 3 for information regarding our investments.

Term Loan

Term Loan	9 Months Ended
	Sep. 30, 2017
Debt Disclosure [Abstract]
Term Loan	Term Loan On June 17, 2016, we entered into a loan and security agreement ("Loan Agreement") with Oxford Finance, LLC, ("Oxford"), pursuant to which Oxford agreed to lend us up to $30.0 million , issuable in two separate term loans of $20.0 million (the "Term A Loan") and $10.0 million (the "Term B Loan"). On June 22, 2016, we received $20.0 million in proceeds from the Term A Loan, net of debt issuance costs. The ability to borrow on the Term B Loan expired on March 31, 2017. We refer to all amounts outstanding under the Loan Agreement as the Term Loan. The outstanding Term Loan will mature on June 1, 2020 (the “Maturity Date”) and we will have interest-only payments through June 1, 2018, followed by 24 equal monthly payments of principal and unpaid accrued interest. The Term Loan will bear interest at a floating per annum rate equal to (i) 8.51% plus (ii) the greater of (a) the 30 day U.S. Dollar LIBOR rate reported in The Wall Street Journal on the last business day of the month that immediately precedes the month in which the interest will accrue and (b) 0.44% . We have the option to prepay all, but not less than all, of the borrowed amount, provided that we will be obligated to pay a prepayment fee equal to (i) 2% of the outstanding principal balance of the Term Loan if prepayment is made prior to the second anniversary of the funding date of the Term Loan, or (ii) 1% of the Term Loan prepaid thereafter and prior to the Maturity Date. We will be required to make a final payment of 5.5% of the principal balance outstanding, payable on the earlier of (i) the Maturity Date, (ii) acceleration of the Term Loan, or (iii) the prepayment of the Term Loan. We may use the proceeds from the Term Loan solely for working capital and to fund our general business requirements. Our obligations under the Loan Agreement are secured by a first priority security interest in substantially all of our current and future assets, other than our intellectual property. We have also agreed not to encumber our intellectual property assets, except as permitted by the Loan Agreement. The Loan Agreement defines certain events of default, including instances of a material adverse change in our operations, that may require prepayment of the outstanding Term Loan. No such events have occurred or are anticipated as of September 30, 2017 . As of September 30, 2017 , we had $20.0 million outstanding under the Term Loan. The Term Loan was recorded at its initial carrying value of $20.0 million , less debt issuance costs of approximately $0.2 million . In connection with the Term Loan, the debt issuance costs have been recorded as a debt discount in our consolidated balance sheets, which are being accreted to interest expense over the life of the Term Loan using an effective interest rate of 8.98% . The exit fee is being accrued over the life of the Term Loan through interest expense. As of September 30, 2017 , we were in compliance with all covenants under the Loan Agreement. Future principal payments for the Term Loan due under the Loan Agreement are as follows (in thousands): 2017 $ — 2018 5,000 2019 10,000 2020 5,000 $ 20,000

Stockholders' Equity

Stockholders' Equity	9 Months Ended
	Sep. 30, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stockholders' Equity	Stockholders’ Equity Shares Reserved for Future Issuance The following shares of common stock were reserved for future issuance as of September 30, 2017 : Common stock options outstanding 10,483,174 Common stock available for future grant under 2012 Equity Incentive Plan 1,240,667 Common stock available for future grant under 2015 Inducement Plan 41,948 Employee Stock Purchase Plan 1,675,110 Total common shares reserved for future issuance 13,440,899 The following table summarizes our stock option activity under all equity incentive plans for the nine months ended September 30, 2017 (shares in thousands): Number of options Weighted average exercise price Options outstanding at December 31, 2016 8,931 $ 6.70 Granted 4,523 $ 1.41 Exercised (11 ) $ 0.38 Canceled/forfeited/expired (2,960 ) $ 6.03 Options outstanding at September 30, 2017 10,483 $ 4.62 Stock-Based Compensation The following table summarizes the weighted average assumptions used to estimate the fair value of stock options and performance stock awards granted to employees under our 2012 Equity Incentive Plan and 2015 Inducement Plan and the shares purchasable under our Employee Stock Purchase Plan during the periods presented: Three months ended Nine months ended 2017 2016 2017 2016 Stock options Risk-free interest rate 1.9 % 1.5 % 2.0 % 1.4 % Volatility 89.5 % 80.0 % 89.4 % 79.9 % Dividend yield — — — — Expected term (years) 6.1 5.7 6.1 5.9 Performance stock options Risk-free interest rate — — 2.1 % 1.4 % Volatility — — 89.9 % 79.3 % Dividend yield — — — — Expected term (years) 0 0 5.6 6.0 Employee stock purchase plan shares Risk-free interest rate 1.0 % 0.5 % 0.8 % 0.5 % Volatility 104.5 % 94.5 % 110.7 % 85.4 % Dividend yield — — — — Expected term (years) 0.5 0.5 0.5 0.5 The following table summarizes the allocation of our stock-based compensation expense for all stock awards during the periods presented, including the adjustments to stock-based compensation expense associated with our May 2017 corporate restructuring (in thousands): Three months ended Nine months ended 2017 2016 2017 2016 Research and development $ 653 $ 1,199 $ 2,411 $ 3,931 Research and development-restructuring related adjustments — — (1,399 ) — General and administrative 631 2,268 2,840 5,522 General and administrative-restructuring related adjustments — — 2,679 — Total $ 1,284 $ 3,467 $ 6,531 $ 9,453 In connection with our May 2017 corporate restructuring we recorded a reversal of stock-based compensation in research and development expenses of $1.4 million as a result of the cancellation of unvested stock options. Additionally, we recorded additional stock-based compensation in general and administrative expenses of $2.7 million as a result of termination provisions within certain employment agreements. These amounts were recorded in the second quarter of 2017. Public Offering In July 2017, we completed an underwritten public offering of 50,600,000 shares of common stock at an offering price of $0.91 per share. We received net proceeds from the offering of $43.0 million after deducting underwriting discounts, commissions and other offering expenses payable by us.

Strategic Alliances and Collabo

Strategic Alliances and Collaborations	9 Months Ended
	Sep. 30, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Strategic Alliances and Collaborations	Strategic Alliances and Collaborations The following table summarizes our total revenues from our strategic alliances and collaborations during the periods presented (in thousands): Three months ended Nine months ended 2017 2016 2017 2016 Sanofi $ 18 $ 18 $ 54 $ 54 AstraZeneca — 186 — 1,122 Total $ 18 $ 204 $ 54 $ 1,176 Sanofi In July 2012, we amended and restated our collaboration and license agreement with Sanofi to expand the potential therapeutic applications of the micro RNA alliance targets to be developed under such agreement. We determined that the elements within the strategic alliance agreement with Sanofi should be treated as a single unit of accounting because the delivered elements did not have stand-alone value to Sanofi. The following elements were delivered as part of the strategic alliance with Sanofi: (1) a license for up to four micro RNA targets; and (2) a research license under our technology alliance. In June 2013, the original research term expired, upon which we and Sanofi entered into an option agreement pursuant to which Sanofi was granted an exclusive right to negotiate the co-development and commercialization of certain of our unencumbered micro RNA programs and we were granted the exclusive right to negotiate with Sanofi for co-development and commercialization of certain miR-21 anti-miRs in oncology and Alport syndrome. In July 2013, we received an upfront payment of $2.5 million , of which $1.25 million is creditable against future amounts payable by Sanofi to us under any future co-development and commercialization agreement we enter pursuant to the option agreement. Revenue associated with the creditable portion of this option payment remained deferred as of September 30, 2017 , and will remain deferred until its application to a creditable transaction. The non-creditable portion of this payment, $1.25 million , was recognized as revenue over the option period from the effective date of the option agreement in June 2013 through the expiration of the option period in January 2014. In February 2014, we and Sanofi entered into a second amended and restated collaboration and license agreement (the “2014 Sanofi Amendment”) to renew our strategic alliance to discover, develop and commercialize micro RNA therapeutics to focus on specific orphan disease and oncology targets. Under the terms of our renewed alliance, Sanofi will have opt-in rights to our clinical fibrosis program targeting miR-21 for the treatment of Alport syndrome, our preclinical program targeting miR-21 for oncology indications, and our preclinical program targeting miR-221/222 for hepatocellular carcinoma (“HCC”). We are responsible for developing each of these programs to proof-of-concept, at which time Sanofi has an exclusive option on each program. If Sanofi chooses to exercise its option on any of these programs, Sanofi will reimburse us for a significant portion of our preclinical and clinical development costs and will also pay us an option exercise fee for any such program, provided that $1.25 million of the $2.5 million upfront option fee paid to us by Sanofi in connection with the June 2013 option agreement will be creditable against such option exercise fee. We are eligible to receive royalties on micro RNA therapeutic products commercialized by Sanofi and will have the right to co-promote these products. In connection with the 2014 Sanofi Amendment, we entered into a Common Stock Purchase Agreement (the “Purchase Agreement”), pursuant to which we sold 1,303,780 shares of our common stock to Aventisub LLC (formerly Aventis Holdings, Inc.) (“Aventis”), an entity affiliated with Sanofi, in a private placement at a price per share of $7.67 for an aggregate purchase price of $10.0 million . Under the terms of the Purchase Agreement, Aventis was not permitted to sell, transfer, make any short sale of, or grant any option for the sale of any common stock for the 12 -month period following its effective date. The Purchase Agreement and the 2014 Sanofi Amendment were negotiated concurrently and were therefore evaluated as a single agreement. Based upon restricted stock studies of similar duration and a Black-Scholes valuation to measure the discount for lack of marketability, approximately $0.4 million of the proceeds from the Purchase Agreement was attributed to the 2014 Sanofi Amendment, and represents consideration for the value of the program targeting miR-221/222 for HCC. As this element does not have stand-alone value, we are recognizing the $0.4 million allocated consideration into revenue ratably over the estimated period of performance of the miR-221/222 program. As of September 30, 2017 , deferred revenue associated with the Purchase Agreement and the 2014 Sanofi Amendment was $0.2 million , which we are expecting to recognize over the remaining estimated period of performance of approximately two years. We are eligible to receive milestone payments of up to $101.8 million for proof-of-concept option exercise fees (net of $1.25 million creditable, as noted above), $15.0 million for clinical milestones and up to $300.0 million for regulatory and commercial milestones. In addition, we are entitled to receive royalties based on a percentage of net sales of any products from the miR-21 and miR-221/222 programs which, in the case of sales in the United States, will be in the middle of the 10 to 20% range, and, in the case of sales outside of the United States, will range from the low end to the middle of the 10 to 20% range, depending upon the volume of sales. If we exercise our option to co-promote a product, we will continue to be eligible to receive royalties on net sales of each product in the United States at the same rate, unless we elect to share a portion of Sanofi’s profits from sales of such product in the United States in lieu of royalties. We have evaluated the contingent event-based payments under the 2014 Sanofi Amendment and determined that the milestone payments meet the definition of substantive milestones. Accordingly, revenue for these achievements will be recognized in their entirety in the period when the milestone is achieved and collectability is reasonably assured. Other contingent event-based payments under the 2014 Sanofi Amendment for which payment is contingent upon the results of Sanofi’s performance will not be accounted for using the milestone method. Such payments will be recognized as revenue over the remaining estimated period of performance, if any, and when collectability is reasonably assured. AstraZeneca In August 2012, we entered into a collaboration and license agreement with AstraZeneca. Under the terms of the agreement, we agreed to collaborate with AstraZeneca to identify, research and develop compounds targeting three micro RNA alliance targets primarily in the fields of cardiovascular diseases, metabolic diseases and oncology. Pursuant to the agreement, we granted AstraZeneca an exclusive, worldwide license to develop, manufacture and commercialize lead compounds designated by AstraZeneca in the course of the collaboration activities against the alliance targets for all human therapeutic uses. Under the terms of the agreement we were required to use commercially reasonable efforts to perform all research, development and manufacturing activities described in the research plan, at our cost, until the acceptance of an investigational new drug application ("IND") or the end of the research term, which expired in August 2016. Under the terms of the agreement, we received an upfront payment of $3.0 million in October 2012. We determined the elements within the agreement should be treated as a single unit of accounting because the delivered element, the license, did not have stand-alone value. As a result, we recognized revenue related to the upfront payment on a straight-line basis over the period of performance, which was four years based on the term of the research and development plan which expired in August 2016. In connection with the collaboration and license agreement and concurrently with our initial public offering, we sold AstraZeneca 6,250,000 shares of our common stock in a private placement at a price per share of $4.00 . Under the terms of the Common Stock Purchase Agreement ("CSPA"), AstraZeneca could not sell, transfer, make any short sale of, or grant any option for the sale of any common stock for a 365 -day period following the effective date of our initial public offering. The CSPA and collaboration and license agreement were negotiated concurrently and were therefore evaluated as a single agreement. Based upon restricted stock studies of similar duration and a Black-Scholes valuation to measure a discount for lack of marketability, $4.3 million was attributed to the collaboration and license agreement. We recognized the $4.3 million into revenue ratably over the period of performance of the research and development plan under the collaboration, which expired in August 2016. In March 2015, we earned a $2.5 million preclinical milestone and in December 2015, we earned a $10.0 million clinical milestone. We determined the milestones to be substantive and recognized revenue upon achievement of each milestone. In June 2017, AstraZeneca delivered written notice of their election to terminate the collaboration and license agreement. Effective upon the termination of the agreement, AstraZeneca’s rights with respect to RG-125(AZD4076) will revert back to us. In accordance with the Agreement, the termination will become effective in June 2018, 12 months following the date of delivery of the notice by AstraZeneca.

Related Party Transactions

Related Party Transactions	9 Months Ended
	Sep. 30, 2017
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions We have entered into certain agreements with related parties in the ordinary course of business to license intellectual property and to procure research and development support services. In September 2014, we entered into an agreement with Sanofi-Aventis Deutschland GmbH (“Sanofi Deutschland”), a contract manufacturing subsidiary of Sanofi, for the manufacture of certain drug substance requirements and other services to support our preclinical and clinical activities associated with the RG-012 program. Pursuant to this agreement, we engaged Sanofi Deutschland to manufacture RG-012 drug product and perform stability studies on our behalf. Expenses incurred under the agreement for services performed or out-of-pocket expenses were less than $0.1 million for the three and nine months ended September 30, 2017 , respectively, compared to $0.2 million and $1.0 million for the same periods in 2016. In February 2015, we entered into a letter agreement with Alnylam Pharmaceuticals, Inc. ("Alnylam") pursuant to which we and Alnylam agreed to the financial terms for certain technology acquired by Alnylam within the licensed patent rights under our Amended and Restated License and Collaboration Agreement (the “Additional Patent Rights”) with Alnylam and Ionis Pharmaceuticals, Inc. In addition to any royalties payable by us to Alnylam pursuant to the terms of the Amended and Restated License and Collaboration Agreement, we agreed to pay Alnylam an additional low single-digit royalty on net sales of certain products utilizing the Additional Patent Rights, with the exact royalty percentage payable being dependent on the total amount of net sales during the calendar year. We also agreed to pay Alnylam milestone payments on certain products utilizing the additional patent rights of up to $33.0 million per product upon the achievement of certain regulatory milestone events. There was no activity under this agreement for the three or nine months ended September 30, 2017 and 2016 .

Basis of Presentation and Sum14

Basis of Presentation and Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2017
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”) for interim financial information and the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. In management’s opinion, the accompanying financial statements reflect all adjustments, consisting of normal recurring adjustments, considered necessary for a fair presentation of the results for the interim periods presented. Interim financial results are not necessarily indicative of results anticipated for the full year. These unaudited condensed financial statements should be read in conjunction with the audited financial statements and footnotes included in our Annual Report on Form 10-K for the year ended December 31, 2016 , from which the balance sheet information herein was derived.
Use of Estimates	Use of Estimates Our condensed financial statements are prepared in accordance with GAAP, which requires us to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses and the disclosure of contingent assets and liabilities in our financial statements and accompanying notes. An estimated loss contingency is accrued in our financial statements if it is probable that a liability has been incurred and the amount of the loss can be reasonably estimated. Although these estimates are based on our knowledge of current events and actions we may undertake in the future, actual results may ultimately differ from these estimates and assumptions.
Revenue Recognition	Revenue Recognition Our revenues generally consist of upfront payments for licenses or options to obtain licenses in the future, milestone payments and payments for other research services under strategic alliance and collaboration agreements. We recognize revenues when all four of the following criteria are met: (1) persuasive evidence of an arrangement exists; (2) delivery of the products and/or services has occurred; (3) the selling price is fixed or determinable; and (4) collectability is reasonably assured. Multiple element arrangements, such as our strategic alliance agreement with Sanofi, are analyzed to determine whether the deliverables within the agreement can be separated or whether they must be accounted for as a single unit of accounting. Deliverables under the agreement will be accounted for as separate units of accounting provided that (i) a delivered item has value to the customer on a stand-alone basis; and (ii) if the agreement includes a general right of return relative to the delivered item, delivery or performance of the undelivered item is considered probable and substantially in the control of the vendor. The allocation of consideration amongst the deliverables under the agreement is derived using a “best estimate of selling price” if vendor specific objective evidence and third-party evidence of fair value is not available. If the delivered element does not have stand-alone value, the arrangement is then accounted for as a single unit of accounting, and we recognize the consideration received under the arrangement as revenue on a straight-line basis, which approximates effort over our estimated period of performance, which for us is typically the expected term of the research and development plan. Milestones We apply the milestone method of accounting to recognize revenue from milestone payments when earned, as evidenced by written acknowledgment from the collaborator or other persuasive evidence that the milestone has been achieved and the payment is non-refundable, provided that the milestone event is substantive. A milestone event is defined as an event (i) that can only be achieved based in whole or in part on either our performance or on the occurrence of a specific outcome resulting from our performance; (ii) for which there is substantive uncertainty at the inception of the arrangement that the event will be achieved; and (iii) that would result in additional payments being due to us. Events for which the occurrence is either contingent solely upon the passage of time or the result of a counterparty’s performance are not considered to be milestone events. A milestone event is substantive if all of the following conditions are met: (i) the consideration is commensurate with either our performance to achieve the milestone, or the enhancement of the value to the delivered item(s) as a result of a specific outcome resulting from our performance to achieve the milestone; (ii) the consideration relates solely to past performance; and (iii) the consideration is reasonable relative to all the deliverables and payment terms (including other potential milestone consideration) within the arrangement. We assess whether a milestone is substantive at the inception of each arrangement. If a milestone is deemed non-substantive, we will account for that milestone payment using a method consistent with the related units of accounting for the arrangement over the estimated performance period. Deferred Revenue Amounts received prior to satisfying the above revenue recognition criteria are recorded as deferred revenue in the accompanying balance sheets. Amounts not expected to be recognized within the next 12 months are classified as non-current deferred revenue.
Stock-Based Compensation	Stock-Based Compensation We account for stock-based compensation expense related to stock options granted to employees and members of our board of directors by estimating the fair value of each stock option on the date of grant using the Black-Scholes option pricing model. We recognize stock-based compensation expense using the accelerated multiple-option approach. Under the accelerated multiple-option approach (also known as the graded-vesting method), we recognize compensation expense over the requisite service period for each separately vesting tranche of the award as though the award was in substance multiple awards, resulting in accelerated expense recognition over the vesting period. For performance-based awards granted to employees (i) the fair value of the award is determined on the grant date, (ii) we assess the probability of the individual milestones under the award being achieved and (iii) the fair value of the shares subject to the milestone is expensed over the implicit service period commencing once management believes the performance criteria is probable of being met. We account for stock options granted to non-employees using the fair value approach. Stock options granted to non-employees are subject to periodic revaluation over their vesting terms.
Clinical Trial and Preclinical Study Accruals	Clinical Trial and Preclinical Study Accruals We make estimates of our accrued expenses for clinical trial and preclinical study activities as of each balance sheet date in our financial statements based on the facts and circumstances known to us at that time. These accruals are based upon estimates of costs incurred and fees that may be associated with services provided by clinical trial investigational sites, clinical research organizations (“CROs”) and for other clinical trial-related activities. Payments under certain contracts with such parties depend on factors such as successful enrollment of patients, site initiation and the completion of clinical trial milestones. In accruing for these services, we estimate the time period over which services will be performed and the level of effort to be expended in each period. If possible, we obtain information regarding unbilled services directly from these service providers. However, we may be required to estimate these services based on other information available to us. If we underestimate or overestimate the activities or fees associated with a study or service at a given point in time, adjustments to research and development expenses may be necessary in future periods. Historically, our estimated accrued liabilities have approximated actual expense incurred. Subsequent changes in estimates may result in a material change in our accruals.
Prepaid Materials	Prepaid Materials We capitalize the purchase of certain raw materials and related supplies for use in the manufacturing of drug product in our clinical development programs, as we have determined that these materials have alternative future use. We can use these raw materials and related supplies in multiple clinical drug products, and therefore have future use independent of the development status of any particular drug program until it is utilized in the manufacturing process. We expense the cost of materials when used. We periodically review these capitalized materials for continued alternative future use and write down the asset to its net realizable value in the period in which it is identified.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606) , which outlines a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance, including industry-specific guidance. ASU 2014-09 outlines a five-step process for revenue recognition that focuses on transfer of control, as opposed to transfer of risk and rewards, and also requires enhanced disclosures regarding the nature, amount, timing and uncertainty of revenues and cash flows from contracts with customers. Major provisions include determining which goods and services are distinct and require separate accounting (performance obligations), how variable consideration (which may include change orders and claims) is recognized, whether revenue should be recognized at a point in time or over time and ensuring the time value of money is considered in the transaction price. The FASB issued supplemental adoption guidance and clarification to ASU No. 2014-09 in March 2016, April 2016 and May 2016 within ASU No. 2016-08, Revenue from Contracts with Customers: Principal vs. Agent Considerations , ASU No. 2016-10, Revenue from Contracts with Customers: Identifying Performance Obligations and Licensing and ASU No. 2016-12, Revenue from Contracts with Customers: Narrow-Scope Improvements and Practical Expedients , respectively. ASU No. 2014-09 and the related supplemental ASUs are effective for fiscal years beginning after December 15, 2017 and interim periods therein. The ASU permits two methods of adoption: the full retrospective method or the modified retrospective method. We plan to apply the modified retrospective method upon adoption in the first quarter of 2018 and currently do not anticipate that the adoption of this ASU will have a material impact with regard to our current contracts. In January 2016, the FASB issued ASU No. 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities , which eliminates the requirement for public companies to disclose the method(s) and significant assumptions used to estimate the fair value for financial instruments measured at amortized cost on the balance sheet. Additionally, the standard requires public companies to use the exit price notion when measuring the fair value of financial instruments for disclosure purposes. Furthermore, the standard requires presentation of financial assets and liabilities by measurement category and form of financial asset on the balance sheet or accompanying notes to the financial statements. The standard is effective for annual reporting periods beginning after December 15, 2017, including interim periods within those annual reporting periods. Early application is permitted. The adoption of this guidance will have no impact on our financial statements. In February 2016, the FASB issued ASU No. 2016-02, Leases, which increases transparency and comparability among organizations by requiring recognition of lease assets and lease liabilities on the balance sheet and disclosure of key information about leasing arrangements. The standard is effective for annual reporting periods beginning after December 15, 2018, including interim periods within those annual reporting periods. Early application is permitted. We are currently evaluating the impact of adoption on our financial statements. In March 2016, the FASB issued ASU No. 2016-09, Compensation – Stock Compensation: Improvements to Employee Share-Based Payment Accounting, which was intended to simplify various aspects of accounting for share-based payment transactions. The new guidance requires immediate recognition of all excess tax benefits and deficiencies in the income statement, requires classification of excess tax benefits as an operating activity as opposed to a financing activity in the statements of cash flows and allows the Company to make an accounting policy election to either estimate the number of awards expected to vest or account for forfeitures when they occur. The standard is effective for annual reporting periods beginning after December 15, 2016, and interim periods within those annual reporting periods. We applied this standard in the first quarter of 2017 using the modified retrospective method of adoption. In conjunction with this adoption, we made an accounting policy election to account for forfeitures as they occur. Upon adoption, we reversed a deferred tax asset related to the balance of unrecognized excess tax benefits of $7.4 million , with an offsetting adjustment to the valuation allowance. Under the modified retrospective method of adoption, we recorded an adjustment of $0.6 million to accumulated deficit with a corresponding offset to additional paid-in capital. In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows: Classification of Certain Cash Receipts and Cash Payments , which addresses the presentation and classification of certain cash receipts and cash payments in the statement of cash flows under Accounting Standards Codification 230. The standard is effective for annual reporting periods beginning after December 15, 2017, and interim periods within those annual reporting periods. The adoption of this guidance will have no impact on our financial statements. In November 2016, the FASB issued ASU No. 2016-18, Statement of Cash Flows: Restricted Cash , which requires restricted cash and restricted cash equivalents to be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. The standard is effective for annual reporting periods beginning after December 15, 2017, and interim periods within those annual reporting periods. Early application is permitted. Upon its adoption in 2018, we will include $1.3 million of restricted cash in our disclosed balance of cash and cash equivalents at the beginning of the period for 2016. We do not expect any additional impact on our financial statements. In May 2017, the FASB issued ASU No. 2017-09, Compensation - Stock Compensation: Scope of Modification Accounting , which provides clarity and guidance around which changes to the terms or conditions of a share-based payment award require an entity to apply modification accounting in Topic 718. The standard is effective for annual reporting periods beginning after December 15, 2017, and interim periods within those annual reporting periods. The adoption of this guidance will have no impact on our financial statements unless we have modification accounting in accordance with Topic 718.
Fair Value Measurement	Fair Value Measurements We have certain financial assets recorded at fair value which have been classified as Level 1, 2, or 3 within the fair value hierarchy as described in the accounting standards for fair value measurements. Accounting standards define fair value as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants as of the measurement date. Market participants are buyers and sellers in the principal market that are (i) independent, (ii) knowledgeable, (iii) able to transact, and (iv) willing to transact. The accounting standards provide an established hierarchy for inputs used in measuring fair value that maximizes the use of observable inputs and minimizes the use of unobservable inputs by requiring that the most observable inputs be used when available. Observable inputs are inputs that market participants would use in valuing the asset or liability and are developed based on market data obtained from independent sources. Unobservable inputs are inputs that reflect our assumptions about the factors that market participants would use in valuing the asset or liability. The accounting standards prioritize the inputs used in measuring the fair value into the following hierarchy: • Level 1 includes financial instruments for which quoted market prices for identical instruments are available in active markets. • Level 2 includes financial instruments for which there are inputs other than quoted prices included within Level 1 that are observable for the instrument such as quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets with insufficient volume or infrequent transactions (less active markets) or model-driven valuations in which significant inputs are observable or can be derived principally from, or corroborated by, observable market data. • Level 3 includes financial instruments for which fair value is derived from valuation techniques in which one or more significant inputs are unobservable, including management’s own assumptions.

Investments (Tables)

Investments (Tables)	9 Months Ended
	Sep. 30, 2017
Investments, Debt and Equity Securities [Abstract]
Summary of Short-Term Investments	The following tables summarize our short-term investments (in thousands): Maturity (in years) Amortized cost Unrealized Estimated fair value Gains Losses As of September 30, 2017 Corporate debt securities 1 or less $ 38,736 $ 1 $ (30 ) $ 38,707 Certificates of deposit 2 or less 6,450 — — 6,450 U.S. Treasury securities 2 or less 4,502 — (6 ) 4,496 Debt securities of U.S. government-sponsored agencies 1 or less 1,497 — (2 ) 1,495 Total $ 51,185 $ 1 $ (38 ) $ 51,148 Maturity (in years) Amortized cost Unrealized Estimated fair value Gains Losses As of December 31, 2016 Corporate debt securities 2 or less $ 49,185 $ 12 $ (77 ) $ 49,120 Certificates of deposit 1 or less 9,291 — — 9,291 Commercial paper 1 or less 1,247 — — 1,247 U.S. Treasury securities 1 or less 1,001 — (1 ) 1,000 Debt securities of U.S. government-sponsored agencies 1 or less 512 — — 512 Total $ 61,236 $ 12 $ (78 ) $ 61,170

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2017
Fair Value Disclosures [Abstract]
Fair Value Hierarchy for Assets and Liabilities Measured at Fair Value on Recurring Basis	The following table presents our fair value hierarchy for assets measured at fair value on a recurring basis as of September 30, 2017 and December 31, 2016 (in thousands): Fair value as of September 30, 2017 Total Level 1 Level 2 Level 3 Assets: Cash equivalents $ 18,078 $ 18,078 $ — $ — Corporate debt securities 38,707 — 38,707 — Certificates of deposit 6,450 — 6,450 — U.S. treasury securities 4,496 — 4,496 — Debt securities of U.S. government-sponsored agencies 1,495 — 1,495 — $ 69,226 $ 18,078 $ 51,148 $ — Fair value as of December 31, 2016 Total Level 1 Level 2 Level 3 Assets: Cash equivalents $ 13,578 $ 13,578 $ — $ — Corporate debt securities 49,120 — 49,120 — Certificates of deposit 9,291 — 9,291 — Commercial paper 1,247 — 1,247 — U.S. treasury securities 1,000 — 1,000 — Debt securities of U.S. government-sponsored agencies 512 — 512 — $ 74,748 $ 13,578 $ 61,170 $ —

Term Loan (Tables)

Term Loan (Tables)	9 Months Ended
	Sep. 30, 2017
Debt Disclosure [Abstract]
Schedule of Future Principal Payments	Future principal payments for the Term Loan due under the Loan Agreement are as follows (in thousands): 2017 $ — 2018 5,000 2019 10,000 2020 5,000 $ 20,000

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	9 Months Ended
	Sep. 30, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Common Stock Reserved for Future Issuance	The following shares of common stock were reserved for future issuance as of September 30, 2017 : Common stock options outstanding 10,483,174 Common stock available for future grant under 2012 Equity Incentive Plan 1,240,667 Common stock available for future grant under 2015 Inducement Plan 41,948 Employee Stock Purchase Plan 1,675,110 Total common shares reserved for future issuance 13,440,899
Stock Option Activity	The following table summarizes our stock option activity under all equity incentive plans for the nine months ended September 30, 2017 (shares in thousands): Number of options Weighted average exercise price Options outstanding at December 31, 2016 8,931 $ 6.70 Granted 4,523 $ 1.41 Exercised (11 ) $ 0.38 Canceled/forfeited/expired (2,960 ) $ 6.03 Options outstanding at September 30, 2017 10,483 $ 4.62
Assumptions Used to Estimate Fair Value of Stock Options and Performance Stock and Employee Stock Purchase Plan	The following table summarizes the weighted average assumptions used to estimate the fair value of stock options and performance stock awards granted to employees under our 2012 Equity Incentive Plan and 2015 Inducement Plan and the shares purchasable under our Employee Stock Purchase Plan during the periods presented: Three months ended Nine months ended 2017 2016 2017 2016 Stock options Risk-free interest rate 1.9 % 1.5 % 2.0 % 1.4 % Volatility 89.5 % 80.0 % 89.4 % 79.9 % Dividend yield — — — — Expected term (years) 6.1 5.7 6.1 5.9 Performance stock options Risk-free interest rate — — 2.1 % 1.4 % Volatility — — 89.9 % 79.3 % Dividend yield — — — — Expected term (years) 0 0 5.6 6.0 Employee stock purchase plan shares Risk-free interest rate 1.0 % 0.5 % 0.8 % 0.5 % Volatility 104.5 % 94.5 % 110.7 % 85.4 % Dividend yield — — — — Expected term (years) 0.5 0.5 0.5 0.5
Stock-Based Compensation	The following table summarizes the allocation of our stock-based compensation expense for all stock awards during the periods presented, including the adjustments to stock-based compensation expense associated with our May 2017 corporate restructuring (in thousands): Three months ended Nine months ended 2017 2016 2017 2016 Research and development $ 653 $ 1,199 $ 2,411 $ 3,931 Research and development-restructuring related adjustments — — (1,399 ) — General and administrative 631 2,268 2,840 5,522 General and administrative-restructuring related adjustments — — 2,679 — Total $ 1,284 $ 3,467 $ 6,531 $ 9,453

Strategic Alliances and Colla19

Strategic Alliances and Collaborations (Tables)	9 Months Ended
	Sep. 30, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Revenue from Strategic Alliances	The following table summarizes our total revenues from our strategic alliances and collaborations during the periods presented (in thousands): Three months ended Nine months ended 2017 2016 2017 2016 Sanofi $ 18 $ 18 $ 54 $ 54 AstraZeneca — 186 — 1,122 Total $ 18 $ 204 $ 54 $ 1,176

Basis of Presentation and Sum20

Basis of Presentation and Summary of Significant Accounting Policies (Detail) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Jun. 30, 2017USD ($)	Sep. 30, 2017USD ($)	Sep. 30, 2016USD ($)	Sep. 30, 2017USD ($)	Sep. 30, 2016USD ($)	May 31, 2017employee	Dec. 31, 2016USD ($)
Property, Plant and Equipment [Line Items]
Workforce reduction, commitment rate						30.00%
Number of employees | employee						65
Severance costs	$ 3,200
Non-cash stock-based compensation	$ 1,300
Cash and cash equivalents and marketable securities		$ 71,400		$ 71,400
Prepaid materials		5,912		5,912			$ 5,552
Stock-based compensation expenses		1,284	$ 3,467	6,531	$ 9,453
Restricted cash							1,300
Prepaid Materials
Property, Plant and Equipment [Line Items]
Prepaid materials		$ 5,900		$ 5,900			$ 5,600

Basis of Presentation and Sum21

Basis of Presentation and Summary of Significant Accounting Policies (Recent Accounting Pronouncements) (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2017	Mar. 31, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Excess tax benefit amount		$ 7,400
Stock-based compensation expenses	$ 1,284		$ 3,467	$ 6,531	$ 9,453
Accounting Standards Update 2016-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stock-based compensation expenses		600
Accounting Standards Update 2016-09 | Additional Paid-in Capital
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle in period of adoption		$ 600

Net Loss Per Share (Detail)

Net Loss Per Share (Detail) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share [Abstract]
Potentially dilutive securities not included in calculation of diluted net loss per share (in shares)	1,281,022	3,131,911	2,531,362	3,762,952

Investments (Summary of Short-T

Investments (Summary of Short-Term Investments) (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Investment [Line Items]
Short term investment maturity weighted average (less than)	2 years
Amortized cost	$ 51,185	$ 61,236
Unrealized Gains	1	12
Unrealized Losses	(38)	(78)
Estimated fair value	$ 51,148	$ 61,170
Corporate debt securities
Investment [Line Items]
Maturity (or less) (in years)	1 year	2 years
Amortized cost	$ 38,736	$ 49,185
Unrealized Gains	1	12
Unrealized Losses	(30)	(77)
Estimated fair value	$ 38,707	$ 49,120
Certificates of deposit
Investment [Line Items]
Maturity (or less) (in years)	1 year	1 year
Amortized cost	$ 6,450	$ 9,291
Unrealized Gains	0	0
Unrealized Losses	0	0
Estimated fair value	$ 6,450	$ 9,291
Commercial paper
Investment [Line Items]
Maturity (or less) (in years)		1 year
Amortized cost		$ 1,247
Unrealized Gains		0
Unrealized Losses		0
Estimated fair value		$ 1,247
U.S. Treasury securities
Investment [Line Items]
Maturity (or less) (in years)	1 year	1 year
Amortized cost	$ 4,502	$ 1,001
Unrealized Gains	0	0
Unrealized Losses	(6)	(1)
Estimated fair value	$ 4,496	$ 1,000
Debt securities of U.S. government-sponsored agencies
Investment [Line Items]
Maturity (or less) (in years)	1 year	1 year
Amortized cost	$ 1,497	$ 512
Unrealized Gains	0	0
Unrealized Losses	(2)	0
Estimated fair value	$ 1,495	$ 512

Fair Value Measurements (Fair V

Fair Value Measurements (Fair Value Hierarchy for Assets and Liabilities Measured at Fair Value on Recurring Basis) (Detail) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	$ 69,226	$ 74,748
Cash equivalents
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	18,078	13,578
Corporate debt securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	38,707	49,120
Certificates of deposit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	6,450	9,291
Commercial paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis		1,247
U.S. Treasury securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	4,496	1,000
Debt securities of U.S. government-sponsored agencies
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	1,495	512
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	18,078	13,578
Level 1 | Cash equivalents
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	18,078	13,578
Level 1 | Corporate debt securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	0	0
Level 1 | Certificates of deposit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	0	0
Level 1 | Commercial paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis		0
Level 1 | U.S. Treasury securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	0	0
Level 1 | Debt securities of U.S. government-sponsored agencies
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	0	0
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	51,148	61,170
Level 2 | Cash equivalents
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	0	0
Level 2 | Corporate debt securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	38,707	49,120
Level 2 | Certificates of deposit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	6,450	9,291
Level 2 | Commercial paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis		1,247
Level 2 | U.S. Treasury securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	4,496	1,000
Level 2 | Debt securities of U.S. government-sponsored agencies
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	1,495	512
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	0	0
Level 3 | Cash equivalents
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	0	0
Level 3 | Corporate debt securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	0	0
Level 3 | Certificates of deposit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	0	0
Level 3 | Commercial paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis		0
Level 3 | U.S. Treasury securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	0	0
Level 3 | Debt securities of U.S. government-sponsored agencies
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	$ 0	$ 0

Term Loan (Details)

Term Loan (Details)	Jun. 22, 2016USD ($)	Jun. 17, 2016USD ($)loan	Sep. 30, 2017USD ($)	Dec. 31, 2016USD ($)
Debt Instrument [Line Items]
Term loan, less debt issuance costs			$ 19,845,000	$ 19,802,000
Debt Financing Agreement
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 30,000,000
Number of term loans | loan		2
Period for principal and interest payments		24 months
Stated interest rate, percentage		8.51%
Prepayment fee, option one			2.00%
Prepayment fee, option two			1.00%
Debt extinguishment fee			5.50%
Term loan, less debt issuance costs			$ 20,000,000
Amounts borrowed			20,000,000
Deferred finance cost			$ 200,000
Debt instrument effective rate			8.98%
Debt Financing Agreement | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate, percentage		0.44%
Debt Financing Agreement Tranche A
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 20,000,000
Proceeds from borrowing under term loan	$ 20,000,000
Term loan, less debt issuance costs			$ 20,000,000
Debt Financing Agreement Tranche B
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 10,000,000

Term Loan (Future Principal Pay

Term Loan (Future Principal Payments) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Long-term Debt	$ 19,845	$ 19,802
Debt Financing Agreement Tranche A
Debt Instrument [Line Items]
Future Repayments of Principal, 2017	0
Future Repayments of Principal, 2018	5,000
Future Repayments of Principal, 2019	10,000
Future Repayments of Principal, 2020	5,000
Long-term Debt	$ 20,000

Stockholders' Equity (Common St

Stockholders' Equity (Common Stock Reserved for Future Issuance) (Detail) - shares	Sep. 30, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock options outstanding	10,483,174	8,931,000
Total common shares reserved for future issuance	13,440,899
Common stock available for future grant under 2012 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock available for future grant	1,240,667
Common stock available for future grant under 2015 Inducement Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock available for future grant	41,948
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock available for future grant	1,675,110

Stockholders' Equity (Stock Opt

Stockholders' Equity (Stock Option Activity) (Detail)	9 Months Ended
	Sep. 30, 2017$ / sharesshares
Number of options
Number of options, beginning outstanding number (in shares) | shares	8,931,000
Number of options, Granted (in shares) | shares	4,523,000
Number of options, Exercised (in shares) | shares	(11,000)
Number of options, Canceled/forfeited/expired (in shares) | shares	(2,960,000)
Number of options, ending outstanding number (in shares) | shares	10,483,174
Weighted average exercise price
Weighted average exercise price, beginning balance (in dollars per share) | $ / shares	$ 6.70
Weighted average exercise price, Granted (in dollars per share) | $ / shares	1.41
Weighted average exercise price, Exercised (in dollars per share) | $ / shares	0.38
Weighted average exercise price, Canceled/forfeited/expired (in dollars per share) | $ / shares	6.03
Weighted average exercise price, ending balance (in dollars per share) | $ / shares	$ 4.62

Stockholders' Equity (Assumptio

Stockholders' Equity (Assumptions Used to Estimate Fair Value of Stock Options and Performance Stock and Employee Stock Purchase Plan) (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Employee Stock Purchase Plan
Weighted average assumptions
Risk-free interest rate	1.00%	0.50%	0.80%	0.50%
Volatility	104.50%	94.50%	110.70%	85.40%
Dividend yield	0.00%	0.00%	0.00%	0.00%
Expected term (years)	6 months	6 months	6 months	6 months
Stock options
Weighted average assumptions
Risk-free interest rate	1.90%	1.50%	2.00%	1.40%
Volatility	89.50%	80.00%	89.40%	79.90%
Dividend yield	0.00%	0.00%	0.00%	0.00%
Expected term (years)	6 years 29 days	5 years 8 months 12 days	6 years 29 days	5 years 10 months 24 days
Performance stock options
Weighted average assumptions
Risk-free interest rate	0.00%	0.00%	2.10%	1.40%
Volatility	0.00%	0.00%	89.90%	79.30%
Dividend yield	0.00%	0.00%	0.00%	0.00%
Expected term (years)	0 years	0 years	5 years 7 months 21 days	6 years

Stockholders' Equity (Stock-Bas

Stockholders' Equity (Stock-Based Compensation Expense Allocation) (Detail) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expenses	$ 1,284		$ 3,467	$ 6,531	$ 9,453
Research and development
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expenses	653		1,199	2,411	3,931
Research and development-restructuring related adjustments
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expenses	0	$ (1,400)	0	(1,399)	0
General and administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expenses	631		2,268	2,840	5,522
General and administrative-restructuring related adjustments
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expenses	$ 0	$ 2,700	$ 0	$ 2,679	$ 0

Stockholders' Equity (Narrative

Stockholders' Equity (Narrative) (Details) - Public Offering $ / shares in Units, $ in Millions	1 Months Ended
	Jul. 31, 2017USD ($)$ / sharesshares
Subsidiary, Sale of Stock [Line Items]
Number of shares issued (in shares) | shares	50,600,000
Sale price per share (USD per share) | $ / shares	$ 0.91
Consideration received | $	$ 43

Strategic Alliances and Colla32

Strategic Alliances and Collaborations (Revenue from Strategic Alliances) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Revenue from External Customer [Line Items]
Total revenues	$ 18	$ 204	$ 54	$ 1,176
Strategic Alliances and Collaborations
Revenue from External Customer [Line Items]
Total revenues	18	204	54	1,176
Strategic Alliances and Collaborations | Sanofi
Revenue from External Customer [Line Items]
Total revenues	18	18	54	54
Strategic Alliances and Collaborations | AstraZeneca
Revenue from External Customer [Line Items]
Total revenues	$ 0	$ 186	$ 0	$ 1,122

Strategic Alliances and Colla33

Strategic Alliances and Collaborations (Detail)	1 Months Ended							8 Months Ended	9 Months Ended
	Dec. 31, 2015USD ($)	Mar. 31, 2015USD ($)	Feb. 28, 2014USD ($)$ / sharesshares	Jul. 31, 2013USD ($)	Oct. 31, 2012USD ($)$ / sharesshares	Aug. 31, 2012target	Jul. 31, 2012target	Jan. 31, 2014USD ($)	Sep. 30, 2017USD ($)shares	Dec. 31, 2016USD ($)shares
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Common stock, shares issued | shares									103,955,147	52,924,805
Common stock value									$ 104,000	$ 53,000
Sanofi
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of collaborative areas granted | target							4
Deferred revenue			$ 400,000
Sanofi | Private Placement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Common stock, shares issued | shares			1,303,780
Price per share (in dollars per share) | $ / shares			$ 7.67
Common stock value			$ 10,000,000
Restriction period in which Alliances could not sell, transfer, make any short sale of, or grant any option for the sale of any common stock			12 months
Sanofi | Minimum | United States
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalties based on percentage of net sales									10.00%
Sanofi | Minimum | Outside of the United States
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalties based on percentage of net sales									10.00%
Sanofi | Maximum | United States
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalties based on percentage of net sales									20.00%
Sanofi | Maximum | Outside of the United States
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalties based on percentage of net sales									20.00%
Sanofi | Development Commercialization And License Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Initial upfront option payment				$ 2,500,000
Deferred revenue creditable against future milestones			$ 1,250,000	$ 1,250,000					$ 1,250,000
Upfront payment non-creditable portion recognized								$ 1,250,000
Sanofi | Common Stock Purchase Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue									$ 200,000
Deferred revenue recognition period									2 years
Sanofi | Proof-of-Concept Trial
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential revenue through milestone payments									$ 101,800,000
Sanofi | Regulatory and Commercialization Milestones
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential revenue through milestone payments									300,000,000
Sanofi | Clinical
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential revenue through milestone payments									$ 15,000,000
AstraZeneca
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of collaborative areas granted | target						3
Initial upfront option payment					$ 3,000,000
Common stock, shares issued | shares					6,250,000
Price per share (in dollars per share) | $ / shares					$ 4
Restriction period in which Alliances could not sell, transfer, make any short sale of, or grant any option for the sale of any common stock					365 days
Deferred revenue					$ 4,300,000
Expected term of research and development plan (years)					4 years
AstraZeneca | Preclinical
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments, earned		$ 2,500,000
AstraZeneca | Clinical
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments, earned	$ 10,000,000

Related Party Transactions (Det

Related Party Transactions (Detail) - USD ($)	1 Months Ended	3 Months Ended		9 Months Ended
	Feb. 28, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Sanofi
Related Party Transaction [Line Items]
Expenses incurred for services performed or out-of-pocket expenses under the Sanofi agreement (less than)		$ 100,000	$ 200,000	$ 100,000	$ 1,000,000
Alnylam
Related Party Transaction [Line Items]
Potential milestone payments to related party	$ 33,000,000