Dicerna Pharmaceuticals (DRNA) 10-K 30 Mar 17 2016 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Mar. 29, 2017	Jun. 30, 2016
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2016
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	FY
Trading Symbol	DRNA
Entity Registrant Name	DICERNA PHARMACEUTICALS INC
Entity Central Index Key	1,399,529
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		20,794,193
Entity Public Float			$ 39.3

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
CURRENT ASSETS:
Cash and cash equivalents	$ 20,865	$ 56,058
Held-to-maturity investments (Note 4)	25,009	38,551
Prepaid expenses and other current assets (Note 5)	1,952	1,532
Total current assets	47,826	96,141
NONCURRENT ASSETS:
Property and equipment-net (Note 6)	2,234	2,684
Restricted cash equivalents (Note 12)	1,116	1,116
Other noncurrent assets	76	82
Total noncurrent assets	3,426	3,882
TOTAL ASSETS	51,252	100,023
CURRENT LIABILITIES:
Accounts payable	4,318	2,621
Accrued expenses and other current liabilities (Note 7)	5,726	6,380
Total current liabilities	10,044	9,001
TOTAL LIABILITIES	10,044	9,001
COMMITMENTS AND CONTINGENCIES (Note 12)
STOCKHOLDERS' EQUITY:
Preferred stock, $0.0001 par value-5,000,000 shares authorized; no shares issued or outstanding at December 31, 2016 or December 31, 2015
Common stock, $0.0001 par value-150,000,000 shares authorized; 20,753,001 and 20,594,575 shares issued and outstanding at December 31, 2016 and 2015, respectively (Note 8)	2	2
Additional paid-in capital (Note 8)	296,962	287,263
Accumulated deficit	(255,756)	(196,243)
Total stockholders' equity	41,208	91,022
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	$ 51,252	$ 100,023

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2016	Dec. 31, 2015
Statement of Financial Position [Abstract]
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	20,753,001	20,594,575
Common stock, shares outstanding	20,753,001	20,594,575

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Statement [Abstract]
Revenue (Note 9)	$ 295	$ 184
Operating expenses:
Research and development	41,694	43,971	$ 29,453
General and administrative	18,349	19,240	15,648
Total operating expenses	60,043	63,211	45,101
Loss from operations	(59,748)	(63,027)	(45,101)
Other income (expense):
Preferred stock warrant liability re-measurement			(2,559)
Loss on extinguishment of debt			(143)
Interest income	235	188	63
Interest expense			(199)
Total other income (expense)	235	188	(2,838)
Net loss	(59,513)	(62,839)	(47,939)
Less: accretion and dividends on redeemable convertible preferred stock			204
Net loss attributable to common stockholders	$ (59,513)	$ (62,839)	$ (48,143)
Net loss per share attributable to common stockholders-basic and diluted	$ (2.87)	$ (3.09)	$ (3)
Weighted average shares outstanding-basic and diluted	20,719,761	20,320,628	16,070,054

Consolidated Statements of Rede

Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity - USD ($) $ in Thousands	Total	Series A Redeemable Convertible Preferred Stock [Member]	Series B Redeemable Convertible Preferred Stock [Member]	Series C Redeemable Convertible Preferred Stock [Member]	Common Stock [Member]	Additional Paid in Capital [Member]	Accumulated Deficit [Member]
Balance at beginning of period at Dec. 31, 2013		$ 21,400	$ 29,050	$ 59,796
Balance at beginning of period at Dec. 31, 2013	$ (68,919)				$ 1	$ 16,545	$ (85,465)
Balance at beginning of period (in shares) at Dec. 31, 2013		855,996	1,162,021	8,571,417
Balance at beginning of period (in shares) at Dec. 31, 2013					38,226
Issuance of Common Stock from initial public offering, net of underwriting fees and issuance costs of $10,751		$ 0	$ 0	$ 0
Issuance of Common Stock from initial public offering, net of underwriting fees and issuance costs of $10,751	92,750				$ 1	92,749
Issuance of Common Stock from initial public offering, net of underwriting fees and issuance costs, Shares					6,900,000
Net exercise of common stock warrant	0	0	0	0	$ 0	0	0
Net exercise of common stock warrant, Shares					12,702
Reclassification of warrants to purchase shares of redeemable convertible preferred stock into a warrant to purchase common stock	3,088					3,088
Accretion of preferred stock issuance costs	(204)			204		(204)
Conversion of preferred stock to common stock		$ (21,400)	$ (29,050)	$ (60,000)
Conversion of preferred stock to common stock	110,452				$ 1	110,451
Conversion of preferred stock to common stock, Shares		855,996	1,162,021	8,571,417	10,589,434
Vesting of restricted common stock	0	$ 0	$ 0	$ 0	$ 0	0	0
Vesting of restricted common stock (in shares)					4,000
Stock-based compensation	8,237					8,237
Exercise of common stock options	824					824
Exercise of common stock options (in shares)					239,853
Sale of common stock related to employee stock purchase plan	51					51
Sale of common stock related to employee stock purchase plan (in shares)					2,652
Net loss	(47,939)						(47,939)
Balance at end of period at Dec. 31, 2014	98,340				$ 3	231,741	(133,404)
Balance at end of period (in shares) at Dec. 31, 2014					17,786,867
Issuance of Common Stock from initial public offering, net of underwriting fees and issuance costs of $10,751		0	0	0
Issuance of Common Stock from initial public offering, net of underwriting fees and issuance costs of $10,751	45,438					45,438
Issuance of Common Stock from initial public offering, net of underwriting fees and issuance costs, Shares					2,750,000
Vesting of restricted common stock	0	0	0	0	$ 0	0	0
Vesting of restricted common stock (in shares)					6,388
Stock-based compensation	9,732					9,732
Exercise of common stock options	149					149
Exercise of common stock options (in shares)					29,506
Settlement of restricted stock for tax withholding	(76)				$ (1)	(75)
Sale of common stock related to employee stock purchase plan	278					278
Sale of common stock related to employee stock purchase plan (in shares)					21,814
Net loss	(62,839)						(62,839)
Balance at end of period at Dec. 31, 2015	91,022				$ 2	287,263	(196,243)
Balance at end of period (in shares) at Dec. 31, 2015					20,594,575
Vesting of restricted common stock	0	$ 0	$ 0	$ 0	$ 0	0	0
Vesting of restricted common stock (in shares)					6,226
Stock-based compensation	9,165					9,165
Exercise of common stock options	$ 396					396
Exercise of common stock options (in shares)	115,699				115,699
Settlement of restricted stock for tax withholding	$ (27)					(27)
Sale of common stock related to employee stock purchase plan	165					165
Sale of common stock related to employee stock purchase plan (in shares)					36,501
Net loss	(59,513)						(59,513)
Balance at end of period at Dec. 31, 2016	$ 41,208				$ 2	$ 296,962	$ (255,756)
Balance at end of period (in shares) at Dec. 31, 2016					20,753,001

Consolidated Statements of Red6

Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Underwriting fees and issuance costs	$ 445	$ 10,751
Series C Redeemable Convertible Preferred Stock [Member]
Underwriting fees and issuance costs	$ 445	$ 10,751

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (59,513)	$ (62,839)	$ (47,939)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	840	727	848
Net amortization of premium/discount on investments	73	134
Stock-based compensation (Note 8)	9,165	9,732	8,237
Loss on extinguishment of debt			143
Increase in fair value of preferred stock warrant			2,559
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(414)	(177)	(1,171)
Accounts payable	1,644	1,384	(97)
Accrued expenses and other liabilities	(542)	2,240	2,656
Net cash used in operating activities	(48,747)	(48,799)	(34,764)
CASH FLOWS FROM INVESTING ACTIVITIES:
Changes in restricted cash equivalents		264	(1,116)
Purchases of property and equipment	(449)	(1,134)	(2,013)
Maturities of held-to-maturity investments	48,500	70,000	9,995
Purchases of held-to-maturity investments	(35,031)	(36,129)	(82,627)
Net cash provided by (used in) investing activities	13,020	33,001	(75,761)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from stock option exercises and issuances under Employee Stock Purchase Plan	561	427	875
Proceeds from public offering of common stock, net of transaction costs (Note 8)		45,438	94,148
Settlement of restricted stock for tax withholding	(27)	(76)
Repayments of long-term debt			(5,026)
Net cash provided by financing activities	534	45,789	89,997
(DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	(35,193)	29,991	(20,528)
CASH AND CASH EQUIVALENTS-Beginning of year	56,058	26,067	46,595
CASH AND CASH EQUIVALENTS-End of year	20,865	56,058	26,067
NONCASH INVESTING ACTIVITIES:
Property and equipment purchases included in accrued expenses	$ 53	$ 112
NONCASH FINANCING ACTIVITIES:
Accretion of redeemable convertible preferred stock			204
SUPPLEMENTAL CASH FLOW INFORMATION:
Warrant conversion to common stock			3,088
Cash paid for interest			$ 194

Description of Business and Bas

Description of Business and Basis of Presentation	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Description of Business and Basis of Presentation	1. Description of Business and Basis of Presentation Business Dicerna Pharmaceuticals, Inc. (the Company) is a biopharmaceutical company focused on the discovery and development of innovative subcutaneously delivered ribonucleic acid (RNA) interference (RNAi)-based pharmaceuticals using its GalXC TM Basis of presentation The accompanying consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (GAAP) and include the accounts of the Dicerna Pharmaceuticals, Inc. and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. Significant judgments and estimates The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, and the disclosure of contingent assets and liabilities at the date of the consolidated financial statements, as well as the revenues and expenses incurred during the reporting periods. On an ongoing basis, the Company evaluates judgments and estimates, including those related to accrued expenses and stock-based compensation. The Company bases its estimates on historical experience and on various other factors that the Company believes are reasonable under the circumstances, the results of which form the basis for making judgments about the carrying value of assets and liabilities that are not apparent from other sources. Changes in estimates are reflected in reported results for the period in which they become known. Actual results could differ materially from those estimates. Liquidity risk The Company’s ability to fund its planned preclinical and clinical operations, including completion of its clinical trials, will depend on its ability to raise capital through a combination of public or private equity offerings, debt financings, and research collaborations and license agreements. If the Company is unable to generate funding from one or more of these sources within a reasonable timeframe, it may have to delay, reduce or terminate its research and development programs, preclinical or clinical trials or undergo reductions in its workforce or other corporate restructuring activities. Based on the Company’s current operating plan, including the receipt of proceeds from the issuance of the Company’s Redeemable Convertible Preferred Stock (see Note 15), management believes that available cash, cash equivalents and held-to-maturity 12-month

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Cash and cash equivalents Cash and cash equivalents include all highly liquid investments, including money market funds, maturing within 90 days from the date of purchase. Held-to-maturity The Company determines the appropriate classification of investments at the time of purchase and re-evaluates held-to-maturity held-to-maturity. Restricted cash equivalents As of December 31, 2016 and 2015, restricted cash equivalents was comprised of a money market collateral account that is restricted and secures the Company’s outstanding letter of credit of $1.1 million for the operating lease for office and laboratory space. The letter of credit is required to be maintained throughout the term of the Company’s lease which expires on December 1, 2020. Concentrations of credit risk Financial instruments that subject the Company to significant concentrations of credit risk consist of cash and cash equivalents, restricted cash equivalents and held-to-maturity held-to-maturity Property and equipment Property and equipment are stated at cost. Major betterments are capitalized whereas expenditures for maintenance and repairs which do not improve or extend the life of the respective assets are charged to operations as incurred. Depreciation is provided using the straight-line method over the estimated useful lives, as shown below. ASSET CATEGORY USEFUL LIVES Office and computer equipment 3-5 Laboratory equipment 5 years Furniture and fixtures 5 years Leasehold improvements 5 years or the remaining term of lease, if shorter Impairment of long-lived assets Long-lived assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of the asset may not be recoverable. When such events occur, the Company compares the carrying amounts of the assets to their undiscounted expected future cash flows. If this comparison indicates that there is an impairment, the amount of the impairment is calculated as the difference between the carrying value and fair value of the related asset. For the years ended December 31, 2016, 2015 and 2014, no impairments have been recorded. Segment and geographic information Operating segments are defined as components (business activity from which it earns revenue and incurs expenses) of an enterprise about which discrete financial information is available and regularly reviewed by the chief operating decision maker in deciding how to allocate resources and in assessing performance. The Company, through its Chief Executive Officer in his role as chief operating decision maker, views its operations and manages its business as one operating segment. All long-lived assets of the Company are located in the United States. Research and development costs Research and development costs consist of expenses incurred in performing research and development activities, including compensation and benefits for full-time research and development employees, an allocation of facility expenses, overhead expenses and other outside expenses. Research and development costs are expensed as incurred. Research and development costs that are paid in advance of performance are deferred as a prepaid expense and amortized over the service period as the services are provided. Stock-based compensation The Company accounts for stock options granted as share-based awards at fair value, which is measured using the Black-Scholes option pricing model. The fair value measurement date for employee awards is the date of grant. The fair value measurement date for nonemployee awards is generally the date the performance of services is completed. Share-based compensation costs are recognized as expense over the requisite service period, which is generally the vesting period, on a straight-line basis for all time-vested awards. For performance-based stock awards, compensation costs are recorded when the Company determines that the achievement of such performance conditions is deemed probable. This determination requires significant judgment by management. At the probable date, the Company records a cumulative expense catch-up, The Company accounts for restricted stock awards granted to employees at fair value, which is measured based upon the quoted closing market price per share of the Company’s common stock on the date of grant, adjusted for assumed forfeitures. The compensation costs are recognized over the vesting period, commencing when the Company determines that it is probable that the awards will vest. Share-based awards to non-employees re-measured Income taxes The Company records deferred tax assets and liabilities for the expected future tax consequences of temporary differences between the Company’s financial statement carrying amounts and the tax basis of assets and liabilities using enacted tax rates expected to be in effect in the years in which the differences are expected to reverse. A valuation allowance is provided to reduce the net deferred tax assets to the amount that will more likely than not be realized. The Company also assesses the probability that the positions taken or expected to be taken in its income tax returns will be sustained by taxing authorities. A “more likely than not” (more than 50 percent) recognition threshold must be met before a tax benefit can be recognized. Tax positions that are more likely than not to be sustained are reflected in the Company’s consolidated financial statements. Tax positions are measured as the largest amount of tax benefit that is greater than 50 percent likely of being realized upon settlement with a taxing authority that has full knowledge of all relevant information. The difference between the benefit recognized for a position and the tax benefit claimed on a tax return is referred to as an unrecognized tax benefit. Potential interest and penalties associated with such uncertain tax positions are recorded as a component of income tax expense. Net loss per common share The Company computes basic net loss per common share by dividing net loss attributable to common stockholders by the weighted average number of common shares outstanding. During periods where the Company earns net income, the Company allocates participating securities a proportional share of net income determined by dividing total weighted average participating securities by the sum of the total weighted average common shares and participating securities (the “two-class non-participating Comprehensive loss The Company has no comprehensive loss items other than net loss. Guarantees and indemnifications The Company is not a guarantor under any agreements. The Company leases office space under an operating lease. The Company has standard indemnification arrangements under these leases that require the Company to indemnify the landlord against losses, liabilities, and claims incurred in connection with the premises covered by the Company’s lease, the Company’s use of the premises, property damage or personal injury, and breach of the agreement. Through December 31, 2016, the Company had not experienced any losses related to this indemnification obligation and no claims with respect thereto were outstanding. The Company does not expect material claims related to this indemnification obligation, and consequently, concluded that the fair value of this obligation is negligible and no related liabilities were established. The Company has indemnified, under pre-determined As permitted under Delaware law, the Company indemnifies its officers, directors, and employees for certain events or occurrences while the officer or director is, or was, serving at the Company’s request in such capacity. The term of the indemnification is for the officer’s or director’s lifetime. Recent Accounting Pronouncements Adopted in 2016 Going concern In August 2014, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2014-15, Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern 2014-15), 2014-15 2014-15 Not yet adopted Revenue recognition In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606), Revenue Recognition Revenue from Contracts with Customers Income taxes In October 2016, the FASB issued ASU No. 2016-16, Accounting for Income Taxes: Intra-Entity Asset Transfers of Assets Other than Inventory 2016-16), 2016-16 pre-tax 2016-16 Leases In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) 2016-02), which 2016-02 2016-02 2016-02 Stock-based compensation In March 2016, the FASB issued ASU No. 2016-09, Compensation—Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting 2016-09), 2016-09 Statement of cash flows In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 230) 2016-15), 2016-15 2016-15 2016-15 In November 2016, the FASB issued ASU No. 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash 2016-18), 2016-18 2016-18

Net Loss Per Share Attributable

Net Loss Per Share Attributable to Common Stockholders	12 Months Ended
	Dec. 31, 2016
Earnings Per Share [Abstract]
Net Loss Per Share Attributable to Common Stockholders	3. Net Loss Per Share Attributable to Common Stockholders The following potentially dilutive securities outstanding during the period, prior to the use of the treasury stock method or if-converted AS OF DECEMBER 31, 2016 2015 2014 Options to purchase common stock 5,099,449 4,297,300 2,764,144 Warrants to purchase common stock 87,901 87,901 80,722 Warrants to purchase redeemable convertible preferred stock — — 12,763 Redeemable convertible preferred stock — — 1,015,426 Unvested restricted stock 20,000 68,656 92,932

Held-to-Maturity Investments

Held-to-Maturity Investments	12 Months Ended
	Dec. 31, 2016
Text Block [Abstract]
Held-to-Maturity Investments	4. Held-to-Maturity The Company invests its excess cash balances in short-term and long-term fixed-income investments. The Company determines the appropriate classification of investments at the time of purchase and re-evaluates held-to-maturity The following tables provide information relating to held-to-maturity AMORTIZED COST GROSS GROSS FAIR VALUE As of December 31, 2016: Held-to-maturity U.S. treasury securities $ 25,009 $ — $ (5 ) $ 25,004 AMORTIZED COST GROSS GROSS FAIR VALUE As of December 31, 2015: Held-to-maturity U.S. treasury securities $ 38,551 $ — $ (47 ) $ 38,504 The amortized cost and fair value of held-to-maturity HELD-TO-MATURITY AMORTIZED FAIR VALUE Maturing in one year or less $ 25,009 $ 25,004 Total $ 25,009 $ 25,004

Prepaid Expenses and Other Curr

Prepaid Expenses and Other Current Assets	12 Months Ended
	Dec. 31, 2016
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid Expenses and Other Current Assets	5. Prepaid Expenses and Other Current Assets Prepaid expenses and other current assets consists of the following: AS OF DECEMBER 31, 2016 2015 Prepaid clinical, contract research and manufacturing costs $ 1,028 $ 649 Prepaid insurance 352 390 Unbilled grant receivable 295 — Interest receivable and other current assets 277 493 Prepaid expenses and other current assets $ 1,952 $ 1,532

Property and Equipment, Net

Property and Equipment, Net	12 Months Ended
	Dec. 31, 2016
Property, Plant and Equipment [Abstract]
Property and Equipment, Net	6. Property and Equipment, Net Property and equipment, net, consists of the following: AS OF DECEMBER 31, 2016 2015 Laboratory equipment $ 4,390 $ 4,161 Office and computer equipment 864 705 Furniture and fixtures 479 477 Leasehold improvements 257 257 Property and equipment—at cost 5,990 5,600 Less accumulated depreciation (3,756 ) (2,916 ) Property and equipment—net $ 2,234 $ 2,684 Depreciation expense for the years ended December 31, 2016, 2015 and 2014 was $0.8 million, $0.7 million and $0.7 million, respectively.

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	12 Months Ended
	Dec. 31, 2016
Text Block [Abstract]
Accrued Expenses and Other Current Liabilities	7. Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities consist of the following: AS OF DECEMBER 31, 2016 2015 Accrued clinical, contract research and manufacturing costs $ 2,313 $ 2,820 Accrued compensation and related benefits 2,113 2,092 Accrued professional fees 867 965 Accrued other expenses 433 503 Accrued expenses and other current liabilities $ 5,726 $ 6,380

Common Stock and Stock Option P

Common Stock and Stock Option Plan	12 Months Ended
	Dec. 31, 2016
Text Block [Abstract]
Common Stock and Stock Option Plan	8. Common Stock and Stock Option Plan Common stock In May 2015, the Company completed the sale of 2,750,000 shares of common stock in a public offering of its common stock at a price to the public of $17.75 per share, resulting in proceeds to the Company of $45.4 million, after deducting underwriting discounts and commissions of approximately $2.9 million and other offering costs of approximately $0.4 million. In February 2014, the Company completed the sale of 6,900,000 shares of common stock in an initial public offering of its common stock at a price to the public of $15.00 per share, resulting in net proceeds to the Company of $92.7 million after deducting underwriting discounts and commissions of approximately $7.2 million and other offering expenses paid by the Company of approximately $3.5 million. Stock option plan On January 14, 2014, the Board of Directors adopted the 2014 Performance Incentive Plan (2014 Plan). The 2014 Plan authorizes the issuances of up to 1,900,000 shares of the Company’s common stock, with an additional 4% of the total outstanding common shares becoming available at each year ending December 31. In June 2015, the 2014 plan was amended to increase the replenishment percentage from 4% to 5% of outstanding common shares annually and to allow the reissuance thereunder of awards and grants that expire or are canceled, terminated, forfeited or fail to vest under previous Board-approved stock plans, as amended. The stock options for new hires generally vest 25% after 12 months, followed by ratable vesting over 36 months and expire 10 years from the grant date. During 2014 and 2015, the Company awarded 470,272 and 450,700 stock options, respectively, as grants as an inducement material to individuals entering into employment with the Company (Inducement Grants). The Inducement Grants were approved by the Compensation Committee of the Company’s Board of Directors and were awarded in accordance with NASDAQ Listing Rule 5635(c)(4) and outside of the 2014 Plan. As such, any shares underlying the Inducement Grants are not, upon forfeiture, cancellation or expiration, included in the pool of shares reserved for future issuance. The fair value of each stock option award is estimated on the date of grant using the Black-Scholes option-pricing model that uses the assumptions noted in the table below. Expected volatility for the Company’s common stock was determined based on an average of the historical volatility of a peer group of similar companies due to limited historical volatility of the Company’s own common stock. The Company also has limited stock option exercise information, and as such, the expected term of stock options granted was calculated using the simplified method, which represents the average of the contractual term of the stock option and the weighted-average vesting period of the stock option. The assumed dividend yield is based upon the Company’s expectation of not paying dividends in the foreseeable future. The risk-free rate for periods within the expected life of the stock option is based upon the U.S. Treasury yield curve in effect at the time of grant. The assumptions used in the Black-Scholes option-pricing model for stock options granted, including Inducement Grants (where applicable), during the years ended December 31, 2016, 2015 and 2014 are as follows: YEARS ENDED DECEMBER 31, 2016 2015 2014 Expected option term (in years) 5.5 – 6.3 5.5 – 6.3 5.5 – 6.3 Expected volatility 71% – 79 % 67% – 71 % 64% – 65 % Risk-free interest rate 1.2% – 2.0 % 1.5% – 1.9 % 1.7% – 2.0 % Expected dividend yield 0.0 % 0.0 % 0.0 % The weighted-average grant date fair value of stock options granted during the years ended December 31, 2016, 2015 and 2014 was $4.60, $9.67, and $9.62 per share, respectively. As of December 31, 2016, there was $13.6 million of unrecognized compensation cost related to unvested employee stock options which are expected to be recognized over a weighted-average period of approximately 2 years. The intrinsic value of stock options exercised was $0.2 million, $0.4 million and $3.2 for the years ended December 31, 2016, 2015 and 2014, respectively. Cash received from stock option exercises for the year ended December 31, 2016 was $0.4 million. A summary of stock option activity for employee and non-employee NUMBER OF OPTIONS WEIGHTED- PRICE PER SHARE WEIGHTED- REMAINING CONTRACTUAL TERM (YEARS) OUTSTANDING—January 1, 2016 4,399,425 $ 12.24 8.1 Granted 1,538,775 7.08 Exercised (115,699 ) 3.42 Forfeited/Canceled (723,052 ) 12.80 OUTSTANDING—December 31, 2016 5,099,449 10.80 7.9 EXERCISABLE—December 31, 2016 2,811,975 11.57 7.4 Vested and expected to vest as of December 31, 2016 5,001,694 $ 10.85 7.9 Under the 2014 Plan, as amended, the Company has reserved 284,620 shares of common stock for future issuance as of December 31, 2016. 2016 Inducement Plan On March 4, 2016, the Board of Directors adopted a plan pursuant to which the Company may grant options to purchase common shares as an inducement to individuals to join the Company (2016 Inducement Plan). The 2016 Inducement Plan allows the Company to deliver up to 250,000 shares (Share Limit) of its common stock to eligible persons, as defined. The Share Limit is subject to adjustment as contemplated by the provisions of the 2014 Plan. No grants were awarded pursuant to the 2016 Inducement Plan during the year ended December 31, 2016. Restricted common stock During 2014, the Company issued a total of 44,000 shares of the Company’s restricted common stock, of which 4,000 shares were fully vested at the grant date and the remaining shares were scheduled to vest in equal tranches over a four-year period on the anniversary date of the related grant. The fair value of these shares were $0.7 million at the grant date. A summary of the Company’s restricted common stock is presented below: SHARES WEIGHTED- GRANT DATE FAIR VALUE PER SHARE Nonvested—December 31, 2015 30,000 $ 16.30 Vested (10,000 ) 16.30 Nonvested—December 31, 2016 20,000 $ 16.30 Restricted common stock outstanding as of December 31, 2016 is expected to vest as follows: 10,000 shares in January 2017 and 10,000 shares in January 2018. As of December 31, 2016 and 2015 the unrecognized compensation cost related to restricted common stock was $0.2 million and $0.4 million, respectively. The total fair value of restricted stock awards that vested during the years ended December 31, 2016, 2015 and 2014 (measured on the date of vesting) was $0.1 million, $0.2 million and $0.1 million, respectively. Stock-based compensation expense is classified in the Company’s consolidated statements of operations as follows: YEARS ENDED DECEMBER 31, 2016 2015 2014 Research and development expenses $ 4,467 $ 4,202 $ 4,183 General and administrative expenses 4,698 5,530 4,054 Total $ 9,165 $ 9,732 $ 8,237 The following table summarizes information about common stock warrants outstanding at December 31, 2016: EXERCISE PRICE NUMBER REMAINING $250.00 2,198 3.46 $7.00 85,703 1.48 87,901 There was no activity recorded with respect to common stock warrants during the year ended December 31, 2016.

Revenue

Revenue	12 Months Ended
	Dec. 31, 2016
Text Block [Abstract]
Revenue	9. Revenue National Institutes of Health (NIH) Grants six-month Collaboration and License Agreement sub-licensable The Company is entitled to receive up to $110.0 million in regulatory, clinical and commercialization milestone payments, and royalties on net sales of each product candidate under the KHK agreement. Since contract inception, the Company has received payments totaling $17.5 million. The Company has not recognized any revenue in connection with the KHK Agreement during the years ended December 31, 2016, 2015 or 2014.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Fair Value Measurements	10. Fair Value Measurements Fair value is an exit price, representing the amount that would be received from the sale of an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. Valuation techniques used to measure fair value are performed in a manner to maximize the use of observable inputs and minimize the use of unobservable inputs. As a basis for considering such assumption the accounting literature establishes a three-tier value hierarchy which prioritizes the inputs used in measuring fair value as follows: (Level 1) observable inputs, such as quoted prices in active markets; (Level 2) inputs other than the quoted prices in active markets that are observable either directly or indirectly; and (Level 3) unobservable inputs for which there is little or no market data, which requires the Company to develop its own assumptions. A summary of the Company’s assets that are measured or disclosed at fair value on a recurring basis as of December 31, 2016 and 2015 are presented below: DESCRIPTION AS OF DECEMBER 31, LEVEL 1 LEVEL 2 LEVEL 3 Cash equivalents Money market fund $ 12,853 $ 12,853 $ — $ — Held-to-maturity U.S. treasury securities 25,004 — 25,004 — Restricted cash equivalents Money market fund 1,116 — 1,116 — Total $ 38,973 $ 12,853 $ 26,120 $ — DESCRIPTION AS OF 2015 LEVEL 1 LEVEL 2 LEVEL 3 Cash equivalents Money market fund $ 45,557 $ 45,557 $ — $ — Held-to-maturity U.S. treasury securities 38,504 — 38,504 — Restricted cash equivalents Money market fund 1,116 — 1,116 — Total $ 85,177 $ 45,557 $ 39,620 $ — The carrying amount of the Company’s cash equivalents, which primarily consist of money market accounts, approximates fair value due to the ability to immediately convert these instruments into cash with minimal expected change in value. Cash equivalents are classified within Level 1 of the fair value hierarchy, because they are valued using quoted prices as of December 31, 2016 and 2015. The Company’s restricted cash equivalents bore interest at the prevailing market rates for instruments with similar characteristics, and, accordingly, the carrying value of these instruments also approximated their fair value. These financial instruments were classified within Level 2 of the fair value hierarchy, because the inputs to the fair value measurement are valued using observable inputs as of December 31, 2016 and 2015. The Company’s held-to-maturity For the years ended December 31, 2016 and 2015, there were no transfers between Level 1 and Level 2.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income Taxes	11. Income Taxes The Company has no current and no deferred income tax expense for the years ended December 31, 2016 and 2015, respectively. The Company did not record a federal income tax provision or benefit for the years ended December 31, 2016 and 2015. The reconciliation between income taxes computed at the federal statutory income tax rate and the provision for (benefit from) income taxes is as follows: YEARS ENDED DECEMBER 31, 2016 2015 2014 Federal statutory rate 34.0 % 34.0 % 34.0 % Effect of: Impact of foreign rate differential (31.4 ) (12.6 ) — Change in valuation allowance — (24.4 ) (32.0 ) Research and development tax credit (0.7 ) 0.9 0.8 Stock-based compensation (0.9 ) (0.9 ) (2.6 ) Other (1.0 ) 3.0 (0.2 ) Total 0.0 % 0.0 % 0.0 % The components of the Company’s deferred tax assets are as follows: AS OF DECEMBER 31, 2016 2015 Deferred tax assets: Net operating loss carryforwards $ 36,727 $ 37,017 Capitalized research and development costs 1,044 2,431 Research and development credit carryforwards 2,982 3,510 Stock compensation 7,298 5,369 Depreciation and other costs (77 ) (74 ) Net deferred tax assets 47,974 48,253 Valuation allowance (47,974 ) (48,253 ) Net deferred tax assets $ — $ — Management has evaluated the positive and negative evidence bearing upon the realizability of the Company’s net deferred tax assets and has determined that it is more likely than not that the Company will not recognize the benefits of the net deferred tax assets. As a result, the Company has recorded a full valuation allowance at December 31, 2016 and 2015. As of December 31, 2016, the Company had approximately $89.7 million of federal and $77.9 million of state net operating loss carryforwards, and $2.4 million of federal and $1.6 million of Massachusetts tax credits that expire starting in 2028 and 2023, respectively. Realization of the future tax benefits is dependent on many factors, including the Company’s ability to generate taxable income within the net operating loss carryforward period. Under the provisions of the Internal Revenue Code, certain substantial changes in the Company’s ownership, including a sale of the Company or significant changes in ownership due to sales of equity, may have limited, or may limit in the future, the amount of net operating loss carryforwards, which could be used annually to offset future taxable income. As of December 31, 2016, the Company had $1.2 million of unrecognized tax benefits, of which $1.2 million would affect income tax expense if recognized, before consideration of the Company’s valuation allowance. The Company does not expect the unrecognized tax benefits to change significantly over the next 12 months. The Company recognizes both interest and penalties associated with uncertain tax positions as a component of income tax expense. As of December 31, 2016 and 2015, the Company had no accrued penalties or provisions for interest. A reconciliation of the gross unrecognized tax benefit is as follows: YEARS ENDED DECEMBER 31, 2016 2015 Unrecognized tax benefits at the beginning of the period $ 1,430 $ 1,216 Additions for current tax positions — 421 Changes for previous tax positions (220 ) (207 ) Unrecognized tax benefits at the end of the period $ 1,210 $ 1,430 The Company files income tax returns in the United States and in the Commonwealth of Massachusetts. The tax years 2007 through 2015 remain open to examination by these jurisdictions, as carryforward attributes generated in past years may be adjusted in a future period. The Company is not currently under examination by the Internal Revenue Service or any other jurisdiction for these years. The Company has not recorded any interest or penalties for unrecognized tax benefits since its inception.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	12. Commitments and Contingencies Facility lease On July 11, 2014, the Company executed a non-cancelable six-year Rent expense was $1.6 million, $1.7 million and $0.7 million for the years ended December 31, 2016, 2015 and 2014, respectively. Future minimum lease payments payable are as follows: PERIOD ENDING DECEMBER 31, OPERATING LEASES 2017 $ 1,582 2018 1,629 2019 1,678 2020 1,581 Total $ 6,470 City of Hope license agreement In September 2007, the Company entered into a license agreement with City of Hope, an independent academic research and medical center (COH). In consideration for the right to develop, manufacture, and commercialize products based on certain of COH’s intellectual property, the Company paid a one-time, non-refundable The Company is required to pay an annual license maintenance fee, reimburse COH for patent costs incurred, pay an amount within the range of $5.0 million to $10.0 million upon the achievement of certain milestones, and pay royalties on any future sales. There were no sublicense or other fees accrued at December 31, 2016, and 2015. The license agreement will remain in effect until the expiration of the last patents or copyrights licensed under the agreement or until all obligations under the agreement with respect to payment of milestones have terminated or expired. The Company may terminate the license agreement at any time upon 90 days written notice to COH. Since September 2007, the Company has made total payments of $5.0 million pursuant to its agreement with COH. The Company recorded research and development expense related to this agreement of $0.1 million, $0.1 million and $0.1 million during the years ended December 31, 2016, 2015 and 2014, respectively. Plant Bioscience Limited license agreement In September 2013, the Company entered into a commercial license agreement with Plant Bioscience Limited (PBL), pursuant to which PBL granted to the Company a license to certain of PBL’s U.S. patents and patent applications to research, discover, develop, manufacture, sell, import and export, products incorporating one or more short RNA molecules (SRMs). Upon signing, the Company paid PBL a one-time, non-refundable Carnegie Institution of Washington license agreement In January 2009, the Company entered into a license agreement with the Carnegie Institution of Washington (Carnegie), pursuant to which Carnegie granted to the Company a worldwide, non-exclusive non-human one-time The agreement with Carnegie will terminate with respect to each licensed product candidate upon the last to expire of any valid claim within the licensed patent rights. Either party may terminate the agreement upon any uncured material breach by the other party. The Company may terminate the agreement at any time for any reason upon written notice to Carnegie. Any patents associated with this license will expire in 2018, removing any obligations. Since January 2009, the Company has made total payments of $0.3 million pursuant to its agreement with Carnegie. The Company recorded research and development expense related to this agreement of $0.03 million during each of the years ended December 31, 2016, 2015 and 2014.

Litigation

Litigation	12 Months Ended
	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Litigation	13. Litigation On June 10, 2015, Alnylam Pharmaceuticals, Inc. (Alnylam) filed a complaint against the Company in the Superior Court of Middlesex County, Massachusetts. The complaint alleges misappropriation of confidential, proprietary, and trade secret information, as well as other related claims, in connection with the Company’s hiring of a number of former employees of Merck and its discussions with Merck regarding the acquisition of its subsidiary, Sirna Therapeutics, Inc., which was subsequently acquired by Alnylam. The complaint seeks among other things, unspecified damages, attorneys’ fees, and an order permanently enjoining the Company from disclosing or using any of Alnylam’s confidential information or trade secrets. The Company believes that these allegations lack merit, has filed an answer denying all liability and intends to continue to vigorously defend all claims asserted. At this time, the Company has not recorded a liability in connection with these matters because it believes that any potential loss is neither probable nor reasonably estimable. From time to time, the Company may be subject to various claims and legal proceedings. If the potential loss from any claim, asserted or unasserted, or legal proceeding is considered probable and the amount is reasonably estimable, the Company will accrue a liability for the estimated loss. There were no litigation liabilities outstanding as of December 31, 2016 and 2015.

Quarterly Financial Data (Unaud

Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Data (Unaudited)	14. Quarterly Financial Data (Unaudited) FIRST SECOND THIRD FOURTH TOTAL 2016 Revenue $ — $ — $ 162 $ 133 $ 295 Net loss (15,693 ) (15,622 ) (14,176 ) (14,022 ) (59,513 ) Net loss attributable to common stockholders (15,693 ) (15,622 ) (14,176 ) (14,022 ) (59,513 ) Net loss per share attributable to common stockholders—basic and diluted $ (0.76 ) $ (0.75 ) $ (0.68 ) $ (0.68 ) $ (2.87 ) FIRST SECOND THIRD FOURTH TOTAL 2015 Revenue $ — $ 184 $ — $ — $ 184 Net loss (14,084 ) (16,176 ) (16,944 ) (15,635 ) (62,839 ) Net loss attributable to common stockholders (14,084 ) (16,176 ) (16,944 ) (15,635 ) (62,839 ) Net loss per share attributable to common stockholders—basic and diluted $ (0.79 ) $ (0.86 ) $ (0.82 ) $ (0.76 ) $ (3.09 ) Net loss per share attributable to common stockholders is based on each reporting period’s weighted average number of shares outstanding, which may differ on a quarter-to-quarter basis. As such, the sum of the quarterly net loss per share attributable to common stockholders amounts may not equal year-to-date net loss per share.

Subsequent event

Subsequent event	12 Months Ended
	Dec. 31, 2016
Subsequent Events [Abstract]
Subsequent event	15. Subsequent event On March 30, 2017, the Company entered into a redeemable convertible preferred stock purchase agreement (SPA) with seven institutional investors (Investors), led by funds advised by Bain Capital Life Sciences L.P. (Lead Investor), pursuant to which the Company agreed to issue and sell in a private placement 700,000 shares of its newly designated Redeemable Convertible Preferred Stock, par value $0.0001 per share (Redeemable Convertible Preferred), at a purchase price of $100.00 per share, for total gross proceeds of $70.0 million (Private Placement). Other participants in the financing include EcoR1 Capital, Cormorant Asset Management, RA Capital, Domain Associates and Skyline Ventures, among others. The Private Placement is expected to close on or before April 11, 2017, subject to the satisfaction of customary closing conditions. The Company plans to file a Certificate of Designation of Redeemable Convertible Preferred Stock (Certificate of Designation) with the Secretary of State of the State of Delaware establishing that each share of Redeemable Convertible Preferred will have a stated value of $100.00 (Stated Value). Pursuant to the Certificate of Designation, the Company shall have the right to require the Investors to convert the Redeemable Convertible Preferred into common stock (Mandatory Conversion), at any time following the earlier of (i) the second anniversary of the closing of the Private Placement or (ii) the occurrence of both of the following: (a) (1) the time that the Company first administers, after the issue date, a dose of a pharmaceutical product candidate (which such product candidate shall be one of the following candidates, or a variation thereof: DCR-PHXC, DCR-PCSK9 or the undisclosed rare disease program currently in pre-clinical development (each, a Product Candidate)) to a human being pursuant to an IND filed by us with the FDA; or (2) after the Company has first administered, after the issue date, a dose of a Product Candidate to a human being pursuant to a clinical trial authorization with the Medicine and Healthcare Products Regulatory Agency in the European Union and an IND relating to such Product Candidate has become effective; and (b) the Company enters into a partnership or license agreement with a major company in the pharmaceutical or biotechnology industry relating to a non-Product Candidate, pursuant to which such company provides the Company with an up-front cash payment of a minimum amount agreed upon by the Company and the Lead Investor and agrees to customary future milestone and royalty payments, provided, that, in each case ((i) and (ii)), the trading price of the Company’s common stock exceeds 200% of the Conversion Price, as defined below, for 45 out of the 60 most recent trading days. The Company’s ability to require conversion shall be subject to (i) a 19.99% blocker provision to comply with NASDAQ Listing Rules (19.99% Conversion Blocker), (ii) if so elected by an investor, a 9.99% blocker provision (9.99% Conversion Blocker) that will prohibit beneficial ownership of more than 9.99% of the outstanding shares of the Company’s common stock or voting power at any time, and (iii) applicable regulatory restrictions. The 19.99% Conversion Blocker and the 9.99% Conversion Blocker are hereinafter referred to as the “Conversion Blockers”. “Conversion Price” shall mean an initial price of $3.19 per share, subject to proportionate adjustment for any stock split, stock dividend, combination or other similar recapitalization event. Following the date of a Mandatory Conversion, any shares of Redeemable Convertible Preferred that are not converted as a result of the Conversion Blockers or applicable regulatory restrictions shall continue to be entitled to all of the rights of the holders of Redeemable Convertible Preferred except that they will no longer be entitled to cumulative dividends, priority distribution of assets upon consummation of a change of control or a liquidation event and certain special voting provisions. On or at any time following the seventh anniversary of the closing of the Private Placement, (i) the Company shall also have the right to redeem the Redeemable Convertible Preferred for a cash consideration equal to the sum of the Accrued Value, as of the date of redemption, plus an amount equal to all accrued or declared and unpaid dividends on the Redeemable Convertible Preferred that have not previously been added to the Accrued Value, and (ii) the holders of a majority of the Redeemable Convertible Preferred shall also have the right to cause the Company to redeem the Redeemable Convertible Preferred at the same price. “Accrued Value” means, with respect to each share of Redeemable Convertible Preferred, the sum of (i) the Stated Value plus (ii) on each quarterly dividend date, an additional amount equal to the dollar value of any dividends on a share of Redeemable Convertible Preferred which have accrued on any dividend payment date and have not previously been added to such Accrued Value. At any time and from time to time at their election, the holders of Redeemable Convertible Preferred will have the option to convert the Redeemable Convertible Preferred into shares of the Company’s common stock by dividing (i) the sum of the Accrued Value plus an amount equal to all accrued or declared and unpaid dividends on the Redeemable Convertible Preferred that have not previously been added to the Accrued Value by (ii) the Conversion Price in effect at the time of such conversion. The conversion of shares of Redeemable Convertible Preferred into shares of common stock is subject to the Conversion Blockers. In the event of the Company’s liquidation, dissolution or winding up, the holder of each share of Redeemable Convertible Preferred will be entitled to receive, in preference to the holders of the common stock and any junior preferred stock, an amount per share equal to the greater of (i) the sum of the Accrued Value plus an amount equal to all accrued or declared and unpaid dividends on the Redeemable Convertible Preferred that have not previously been added to the Accrued Value, or (ii) the amount that such shares would have been entitled to receive if they had converted into common stock immediately prior to such liquidation, dissolution or winding up. Upon consummation of a specified change of control transaction, each holder of Redeemable Convertible Preferred will be entitled to receive in preference to the holders of common stock and any junior preferred stock, an amount equal to the greater of (i) 101% of the sum of the Accrued Value plus an amount equal to all accrued or declared and unpaid dividends on the Redeemable Convertible Preferred that have not previously been added to the Accrued Value, or (ii) the amount that such shares would have been entitled to receive if they had converted into common stock immediately prior to such event. In addition, for so long as any shares of Redeemable Convertible Preferred remain outstanding, without the approval of holders of a majority of the Redeemable Convertible Preferred, the Company may not, among other things, (i) amend, modify or fail to give effect to any right of holders of the Redeemable Convertible Preferred, (ii) change the authorized number of Redeemable Convertible Preferred or issue additional Redeemable Convertible Preferred or create a new class or series of equity securities or securities convertible into equity securities with equal or superior rights, preferences or privileges to those of the Redeemable Convertible Preferred in terms of liquidation preference, dividend rights or certain governance rights, (iii) issue shares of common stock or securities convertible into common stock while the Company has insufficient shares to effect the conversion of the Redeemable Convertible Preferred into common stock, (iv) declare or pay dividends or redeem or repurchase any capital stock (other than certain repurchases from employees, directors, advisors or consultants upon termination of service) or (v) incur certain indebtedness in excess of $10 million. Except as set forth above or as otherwise required by law, holders of shares of Redeemable Convertible Preferred are entitled to vote together with shares of common stock (based on one vote per share of common stock into which the shares of Redeemable Convertible Preferred are convertible on the applicable record date) on any matter on which the holders of common stock are entitled to vote. Upon the effectiveness of the Certificate of Designation, each holder of Redeemable Convertible Preferred will be entitled to receive cumulative dividends on the Accrued Value of each share of Redeemable Convertible Preferred at an initial rate of 12% per annum, compounded quarterly and subject to two rate reductions, of 4% each, upon the occurrence of certain agreed-upon milestone events. Dividends on the Redeemable Convertible Preferred are payable in kind and will accrue on the Accrued Value of each share of Redeemable Convertible Preferred until the earlier of conversion, redemption, consummation of a change of control, a liquidation event, or upon failure to mandatorily convert due to the Conversion Blockers or applicable regulatory restrictions. In accordance with the terms of the SPA, on March 28, 2017, the Company’s board of directors voted to increase the size of the board from eight directors to nine directors and appointed Adam M. Koppel, M.D., Ph.D., a managing director of the Lead Investor, as a director of the Company, effective immediately following, and contingent upon, the closing of the Private Placement, to fill the resulting vacancy. To the extent such director is not reelected at any time and, so long as the Lead Investor owns at least 25% of the Redeemable Convertible Preferred (or underlying common stock) owned by it at the closing of the Private Placement, it shall have the right to designate a board observer. The Company also expects to enter into an amended and restated registration rights agreement, by and among the Company and the Investors (Registration Rights Agreement). Pursuant to the Registration Rights Agreement, the Investors will be entitled to certain demand, shelf and “piggyback” registration rights with respect to the shares of common stock issuable upon conversion of the Redeemable Convertible Preferred, subject to the limitations set forth in the Registration Rights Agreement. The shares of Redeemable Convertible Preferred and the shares of common stock issuable upon conversion of the Redeemable Convertible Preferred are expected to be offered and sold by the Company pursuant to an exemption from the registration requirements of the Securities Act provided by Section 4(a)(2) thereunder.

Description of Business and B23

Description of Business and Basis of Presentation (Policies)	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Business	Business Dicerna Pharmaceuticals, Inc. (the Company) is a biopharmaceutical company focused on the discovery and development of innovative subcutaneously delivered ribonucleic acid (RNA) interference (RNAi)-based pharmaceuticals using its GalXC TM
Basis of presentation	Basis of presentation The accompanying consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (GAAP) and include the accounts of the Dicerna Pharmaceuticals, Inc. and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation.
Significant judgments and estimates	Significant judgments and estimates The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, and the disclosure of contingent assets and liabilities at the date of the consolidated financial statements, as well as the revenues and expenses incurred during the reporting periods. On an ongoing basis, the Company evaluates judgments and estimates, including those related to accrued expenses and stock-based compensation. The Company bases its estimates on historical experience and on various other factors that the Company believes are reasonable under the circumstances, the results of which form the basis for making judgments about the carrying value of assets and liabilities that are not apparent from other sources. Changes in estimates are reflected in reported results for the period in which they become known. Actual results could differ materially from those estimates.
Liquidity risk	Liquidity risk The Company’s ability to fund its planned preclinical and clinical operations, including completion of its clinical trials, will depend on its ability to raise capital through a combination of public or private equity offerings, debt financings, and research collaborations and license agreements. If the Company is unable to generate funding from one or more of these sources within a reasonable timeframe, it may have to delay, reduce or terminate its research and development programs, preclinical or clinical trials or undergo reductions in its workforce or other corporate restructuring activities. Based on the Company’s current operating plan, including the receipt of proceeds from the issuance of the Company’s Redeemable Convertible Preferred Stock (see Note 15), management believes that available cash, cash equivalents and held-to-maturity 12-month
Cash and cash equivalents	Cash and cash equivalents Cash and cash equivalents include all highly liquid investments, including money market funds, maturing within 90 days from the date of purchase.
Held-to-maturity investments	Held-to-maturity The Company determines the appropriate classification of investments at the time of purchase and re-evaluates held-to-maturity held-to-maturity.
Restricted cash equivalents	Restricted cash equivalents As of December 31, 2016 and 2015, restricted cash equivalents was comprised of a money market collateral account that is restricted and secures the Company’s outstanding letter of credit of $1.1 million for the operating lease for office and laboratory space. The letter of credit is required to be maintained throughout the term of the Company’s lease which expires on December 1, 2020.
Concentrations of credit risk	Concentrations of credit risk Financial instruments that subject the Company to significant concentrations of credit risk consist of cash and cash equivalents, restricted cash equivalents and held-to-maturity held-to-maturity
Property and equipment	Property and equipment Property and equipment are stated at cost. Major betterments are capitalized whereas expenditures for maintenance and repairs which do not improve or extend the life of the respective assets are charged to operations as incurred. Depreciation is provided using the straight-line method over the estimated useful lives, as shown below. ASSET CATEGORY USEFUL LIVES Office and computer equipment 3-5 Laboratory equipment 5 years Furniture and fixtures 5 years Leasehold improvements 5 years or the remaining term of lease, if shorter
Impairment of long-lived assets	Impairment of long-lived assets Long-lived assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of the asset may not be recoverable. When such events occur, the Company compares the carrying amounts of the assets to their undiscounted expected future cash flows. If this comparison indicates that there is an impairment, the amount of the impairment is calculated as the difference between the carrying value and fair value of the related asset. For the years ended December 31, 2016, 2015 and 2014, no impairments have been recorded.
Segment and geographic information	Segment and geographic information Operating segments are defined as components (business activity from which it earns revenue and incurs expenses) of an enterprise about which discrete financial information is available and regularly reviewed by the chief operating decision maker in deciding how to allocate resources and in assessing performance. The Company, through its Chief Executive Officer in his role as chief operating decision maker, views its operations and manages its business as one operating segment. All long-lived assets of the Company are located in the United States.
Research and development costs	Research and development costs Research and development costs consist of expenses incurred in performing research and development activities, including compensation and benefits for full-time research and development employees, an allocation of facility expenses, overhead expenses and other outside expenses. Research and development costs are expensed as incurred. Research and development costs that are paid in advance of performance are deferred as a prepaid expense and amortized over the service period as the services are provided.
Stock-based compensation	Stock-based compensation The Company accounts for stock options granted as share-based awards at fair value, which is measured using the Black-Scholes option pricing model. The fair value measurement date for employee awards is the date of grant. The fair value measurement date for nonemployee awards is generally the date the performance of services is completed. Share-based compensation costs are recognized as expense over the requisite service period, which is generally the vesting period, on a straight-line basis for all time-vested awards. For performance-based stock awards, compensation costs are recorded when the Company determines that the achievement of such performance conditions is deemed probable. This determination requires significant judgment by management. At the probable date, the Company records a cumulative expense catch-up, The Company accounts for restricted stock awards granted to employees at fair value, which is measured based upon the quoted closing market price per share of the Company’s common stock on the date of grant, adjusted for assumed forfeitures. The compensation costs are recognized over the vesting period, commencing when the Company determines that it is probable that the awards will vest. Share-based awards to non-employees re-measured
Income taxes	Income taxes The Company records deferred tax assets and liabilities for the expected future tax consequences of temporary differences between the Company’s financial statement carrying amounts and the tax basis of assets and liabilities using enacted tax rates expected to be in effect in the years in which the differences are expected to reverse. A valuation allowance is provided to reduce the net deferred tax assets to the amount that will more likely than not be realized. The Company also assesses the probability that the positions taken or expected to be taken in its income tax returns will be sustained by taxing authorities. A “more likely than not” (more than 50 percent) recognition threshold must be met before a tax benefit can be recognized. Tax positions that are more likely than not to be sustained are reflected in the Company’s consolidated financial statements. Tax positions are measured as the largest amount of tax benefit that is greater than 50 percent likely of being realized upon settlement with a taxing authority that has full knowledge of all relevant information. The difference between the benefit recognized for a position and the tax benefit claimed on a tax return is referred to as an unrecognized tax benefit. Potential interest and penalties associated with such uncertain tax positions are recorded as a component of income tax expense.
Net loss per common share	Net loss per common share The Company computes basic net loss per common share by dividing net loss attributable to common stockholders by the weighted average number of common shares outstanding. During periods where the Company earns net income, the Company allocates participating securities a proportional share of net income determined by dividing total weighted average participating securities by the sum of the total weighted average common shares and participating securities (the “two-class non-participating
Comprehensive loss	Comprehensive loss The Company has no comprehensive loss items other than net loss.
Guarantees and indemnifications	Guarantees and indemnifications The Company is not a guarantor under any agreements. The Company leases office space under an operating lease. The Company has standard indemnification arrangements under these leases that require the Company to indemnify the landlord against losses, liabilities, and claims incurred in connection with the premises covered by the Company’s lease, the Company’s use of the premises, property damage or personal injury, and breach of the agreement. Through December 31, 2016, the Company had not experienced any losses related to this indemnification obligation and no claims with respect thereto were outstanding. The Company does not expect material claims related to this indemnification obligation, and consequently, concluded that the fair value of this obligation is negligible and no related liabilities were established. The Company has indemnified, under pre-determined As permitted under Delaware law, the Company indemnifies its officers, directors, and employees for certain events or occurrences while the officer or director is, or was, serving at the Company’s request in such capacity. The term of the indemnification is for the officer’s or director’s lifetime.
Recent Accounting Pronouncements	Recent Accounting Pronouncements Adopted in 2016 Going concern In August 2014, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2014-15, Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern 2014-15), 2014-15 2014-15 Not yet adopted Revenue recognition In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606), Revenue Recognition Revenue from Contracts with Customers Income taxes In October 2016, the FASB issued ASU No. 2016-16, Accounting for Income Taxes: Intra-Entity Asset Transfers of Assets Other than Inventory 2016-16), 2016-16 pre-tax 2016-16 Leases In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) 2016-02), which 2016-02 2016-02 2016-02 Stock-based compensation In March 2016, the FASB issued ASU No. 2016-09, Compensation—Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting 2016-09), 2016-09 Statement of cash flows In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 230) 2016-15), 2016-15 2016-15 2016-15 In November 2016, the FASB issued ASU No. 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash 2016-18), 2016-18 2016-18

Summary of Significant Accoun24

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Estimated Useful Lives	Depreciation is provided using the straight-line method over the estimated useful lives, as shown below. ASSET CATEGORY USEFUL LIVES Office and computer equipment 3-5 Laboratory equipment 5 years Furniture and fixtures 5 years Leasehold improvements 5 years or the remaining term of lease, if shorter

Net Loss Per Share Attributab25

Net Loss Per Share Attributable to Common Stockholders (Tables)	12 Months Ended
	Dec. 31, 2016
Earnings Per Share [Abstract]
Schedule of Dilutive Securities Outstanding	The following potentially dilutive securities outstanding during the period, prior to the use of the treasury stock method or if-converted AS OF DECEMBER 31, 2016 2015 2014 Options to purchase common stock 5,099,449 4,297,300 2,764,144 Warrants to purchase common stock 87,901 87,901 80,722 Warrants to purchase redeemable convertible preferred stock — — 12,763 Redeemable convertible preferred stock — — 1,015,426 Unvested restricted stock 20,000 68,656 92,932

Held-to-Maturity Investments (T

Held-to-Maturity Investments (Tables)	12 Months Ended
	Dec. 31, 2016
Text Block [Abstract]
Schedule of Held-To-Maturity Investments	The following tables provide information relating to held-to-maturity AMORTIZED COST GROSS GROSS FAIR VALUE As of December 31, 2016: Held-to-maturity U.S. treasury securities $ 25,009 $ — $ (5 ) $ 25,004 AMORTIZED COST GROSS GROSS FAIR VALUE As of December 31, 2015: Held-to-maturity U.S. treasury securities $ 38,551 $ — $ (47 ) $ 38,504
Amortized Cost and Fair Value of Held-To-Maturity Investments	The amortized cost and fair value of held-to-maturity HELD-TO-MATURITY AMORTIZED FAIR VALUE Maturing in one year or less $ 25,009 $ 25,004 Total $ 25,009 $ 25,004

Prepaid Expenses and Other Cu27

Prepaid Expenses and Other Current Assets (Tables)	12 Months Ended
	Dec. 31, 2016
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Summary of Prepaid Expenses and Other Current Assets	Prepaid expenses and other current assets consists of the following: AS OF DECEMBER 31, 2016 2015 Prepaid clinical, contract research and manufacturing costs $ 1,028 $ 649 Prepaid insurance 352 390 Unbilled grant receivable 295 — Interest receivable and other current assets 277 493 Prepaid expenses and other current assets $ 1,952 $ 1,532

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	12 Months Ended
	Dec. 31, 2016
Property, Plant and Equipment [Abstract]
Summary of Property and Equipment, Net	Property and equipment, net, consists of the following: AS OF DECEMBER 31, 2016 2015 Laboratory equipment $ 4,390 $ 4,161 Office and computer equipment 864 705 Furniture and fixtures 479 477 Leasehold improvements 257 257 Property and equipment—at cost 5,990 5,600 Less accumulated depreciation (3,756 ) (2,916 ) Property and equipment—net $ 2,234 $ 2,684

Accrued Expenses and Other Cu29

Accrued Expenses and Other Current Liabilities (Tables)	12 Months Ended
	Dec. 31, 2016
Text Block [Abstract]
Schedule of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consist of the following: AS OF DECEMBER 31, 2016 2015 Accrued clinical, contract research and manufacturing costs $ 2,313 $ 2,820 Accrued compensation and related benefits 2,113 2,092 Accrued professional fees 867 965 Accrued other expenses 433 503 Accrued expenses and other current liabilities $ 5,726 $ 6,380

Common Stock and Stock Option30

Common Stock and Stock Option Plan (Tables)	12 Months Ended
	Dec. 31, 2016
Text Block [Abstract]
Assumptions Used in the Black-Scholes Option-Pricing Model for Stock Options Granted	The assumptions used in the Black-Scholes option-pricing model for stock options granted, including Inducement Grants (where applicable), during the years ended December 31, 2016, 2015 and 2014 are as follows: YEARS ENDED DECEMBER 31, 2016 2015 2014 Expected option term (in years) 5.5 – 6.3 5.5 – 6.3 5.5 – 6.3 Expected volatility 71% – 79 % 67% – 71 % 64% – 65 % Risk-free interest rate 1.2% – 2.0 % 1.5% – 1.9 % 1.7% – 2.0 % Expected dividend yield 0.0 % 0.0 % 0.0 %
Stock Option Activity for Employee and Nonemployee	A summary of stock option activity for employee and non-employee NUMBER OF OPTIONS WEIGHTED- PRICE PER SHARE WEIGHTED- REMAINING CONTRACTUAL TERM (YEARS) OUTSTANDING—January 1, 2016 4,399,425 $ 12.24 8.1 Granted 1,538,775 7.08 Exercised (115,699 ) 3.42 Forfeited/Canceled (723,052 ) 12.80 OUTSTANDING—December 31, 2016 5,099,449 10.80 7.9 EXERCISABLE—December 31, 2016 2,811,975 11.57 7.4 Vested and expected to vest as of December 31, 2016 5,001,694 $ 10.85 7.9
Summary of Company's Restricted Common Stock	A summary of the Company’s restricted common stock is presented below: SHARES WEIGHTED- GRANT DATE FAIR VALUE PER SHARE Nonvested—December 31, 2015 30,000 $ 16.30 Vested (10,000 ) 16.30 Nonvested—December 31, 2016 20,000 $ 16.30
Stock-Based Compensation Expense	Stock-based compensation expense is classified in the Company’s consolidated statements of operations as follows: YEARS ENDED DECEMBER 31, 2016 2015 2014 Research and development expenses $ 4,467 $ 4,202 $ 4,183 General and administrative expenses 4,698 5,530 4,054 Total $ 9,165 $ 9,732 $ 8,237
Summary of Common Stock Warrants Outstanding	The following table summarizes information about common stock warrants outstanding at December 31, 2016: EXERCISE PRICE NUMBER REMAINING $250.00 2,198 3.46 $7.00 85,703 1.48 87,901

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Schedule of Assets Measured or Disclosed at Fair Value on Recurring Basis	A summary of the Company’s assets that are measured or disclosed at fair value on a recurring basis as of December 31, 2016 and 2015 are presented below: DESCRIPTION AS OF DECEMBER 31, LEVEL 1 LEVEL 2 LEVEL 3 Cash equivalents Money market fund $ 12,853 $ 12,853 $ — $ — Held-to-maturity U.S. treasury securities 25,004 — 25,004 — Restricted cash equivalents Money market fund 1,116 — 1,116 — Total $ 38,973 $ 12,853 $ 26,120 $ — DESCRIPTION AS OF 2015 LEVEL 1 LEVEL 2 LEVEL 3 Cash equivalents Money market fund $ 45,557 $ 45,557 $ — $ — Held-to-maturity U.S. treasury securities 38,504 — 38,504 — Restricted cash equivalents Money market fund 1,116 — 1,116 — Total $ 85,177 $ 45,557 $ 39,620 $ —

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Reconciliation Between Income Taxes Computed at the Federal Statutory Income Tax Rate and the Provision	The reconciliation between income taxes computed at the federal statutory income tax rate and the provision for (benefit from) income taxes is as follows: YEARS ENDED DECEMBER 31, 2016 2015 2014 Federal statutory rate 34.0 % 34.0 % 34.0 % Effect of: Impact of foreign rate differential (31.4 ) (12.6 ) — Change in valuation allowance — (24.4 ) (32.0 ) Research and development tax credit (0.7 ) 0.9 0.8 Stock-based compensation (0.9 ) (0.9 ) (2.6 ) Other (1.0 ) 3.0 (0.2 ) Total 0.0 % 0.0 % 0.0 %
Deferred Tax Assets	The components of the Company’s deferred tax assets are as follows: AS OF DECEMBER 31, 2016 2015 Deferred tax assets: Net operating loss carryforwards $ 36,727 $ 37,017 Capitalized research and development costs 1,044 2,431 Research and development credit carryforwards 2,982 3,510 Stock compensation 7,298 5,369 Depreciation and other costs (77 ) (74 ) Net deferred tax assets 47,974 48,253 Valuation allowance (47,974 ) (48,253 ) Net deferred tax assets $ — $ —
Unrecognized Tax Benefit	A reconciliation of the gross unrecognized tax benefit is as follows: YEARS ENDED DECEMBER 31, 2016 2015 Unrecognized tax benefits at the beginning of the period $ 1,430 $ 1,216 Additions for current tax positions — 421 Changes for previous tax positions (220 ) (207 ) Unrecognized tax benefits at the end of the period $ 1,210 $ 1,430

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Summary of Future Minimum Lease Payments Payable	Future minimum lease payments payable are as follows: PERIOD ENDING DECEMBER 31, OPERATING LEASES 2017 $ 1,582 2018 1,629 2019 1,678 2020 1,581 Total $ 6,470

Quarterly Financial Data (Una34

Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Financial Data	FIRST QUARTER SECOND QUARTER THIRD QUARTER FOURTH QUARTER TOTAL YEAR 2016 Revenue $ — $ — $ 162 $ 133 $ 295 Net loss (15,693 ) (15,622 ) (14,176 ) (14,022 ) (59,513 ) Net loss attributable to common stockholders (15,693 ) (15,622 ) (14,176 ) (14,022 ) (59,513 ) Net loss per share attributable to common stockholders—basic and diluted $ (0.76 ) $ (0.75 ) $ (0.68 ) $ (0.68 ) $ (2.87 ) FIRST QUARTER SECOND QUARTER THIRD QUARTER FOURTH QUARTER TOTAL YEAR 2015 Revenue $ — $ 184 $ — $ — $ 184 Net loss (14,084 ) (16,176 ) (16,944 ) (15,635 ) (62,839 ) Net loss attributable to common stockholders (14,084 ) (16,176 ) (16,944 ) (15,635 ) (62,839 ) Net loss per share attributable to common stockholders—basic and diluted $ (0.79 ) $ (0.86 ) $ (0.82 ) $ (0.76 ) $ (3.09 )

Summary of Significant Accoun35

Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2016USD ($)Segment	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)
Schedule Of Significant Accounting Policies [Line Items]
Counterparty accounted for all of the Company's revenue and research and license agreement receivable	During 2016 and 2015, one counterparty accounted for all of the Company's revenue.
Long-lived assets, impairment charge	$ 0	$ 0	$ 0
Number of operating segment | Segment	1
Money Market Fund [Member]
Schedule Of Significant Accounting Policies [Line Items]
Lease Expiration Date	Dec. 1, 2020
Letter of credit	$ 1,100,000	$ 1,100,000

Summary of Significant Accoun36

Summary of Significant Accounting Policies - Estimated Useful Lives (Detail)	12 Months Ended
	Dec. 31, 2016
Office and Computer Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Useful Lives	3 years
Office and Computer Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Useful Lives	5 years
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Useful Lives	5 years
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Useful Lives	5 years
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Useful Lives	5 years or the remaining term of lease, if shorter

Net Loss Per Share Attributab37

Net Loss Per Share Attributable to Common Stockholders - Schedule of Dilutive Securities Outstanding (Detail) - shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Employee Stock Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities	5,099,449	4,297,300	2,764,144
Hercules Warrants [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities	87,901	87,901	80,722
Warrants to Purchase Redeemable Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities			12,763
Redeemable Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities			1,015,426
Unvested Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities	20,000	68,656	92,932

Held-to-Maturity Investments -

Held-to-Maturity Investments - Schedule of Held-to-Maturity Investments (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity investments, Amortized Cost	$ 25,009
Held-to-maturity investments, Fair Value, Total	25,004
US Treasury Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity investments, Amortized Cost	25,009	$ 38,551
Held-to-maturity investments, Gross Unrealized Gains	0	0
Held-to-maturity investments, Gross Unrealized Losses	(5)	(47)
Held-to-maturity investments, Fair Value, Total	$ 25,004	$ 38,504

Held-to-Maturity Investments 39

Held-to-Maturity Investments - Amortized Cost and Fair Value of Held-to-Maturity Investments (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Held-to-Maturity securities, Maturing in one year or less, Amortized Cost	$ 25,009	$ 38,551
Held to Maturity, Amortized Cost, Total	25,009
Held-to-Maturity securities, Maturing in one year or less, Fair Value	25,004
Held-to-Maturity, Fair Value, Total	$ 25,004

Prepaid Expenses and Other Cu40

Prepaid Expenses and Other Current Assets - Summary of Prepaid Expenses and Other Current Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid clinical, contract research and manufacturing costs	$ 1,028	$ 649
Prepaid insurance	352	390
Unbilled grant receivable	295
Interest receivable and other current assets	277	493
Prepaid expenses and other current assets	$ 1,952	$ 1,532

Property and Equipment, Net - S

Property and Equipment, Net - Summary of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Property and equipment-at cost	$ 5,990	$ 5,600
Less accumulated depreciation	(3,756)	(2,916)
Property and equipment-net	2,234	2,684
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment-at cost	4,390	4,161
Office and Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment-at cost	864	705
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment-at cost	479	477
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment-at cost	$ 257	$ 257

Property and Equipment, Net - A

Property and Equipment, Net - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 0.8	$ 0.7	$ 0.7

Accrued Expenses and Other Cu43

Accrued Expenses and Other Current Liabilities - Schedule of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Payables and Accruals [Abstract]
Accrued clinical, contract research and manufacturing costs	$ 2,313	$ 2,820
Accrued compensation and related benefits	2,113	2,092
Accrued professional fees	867	965
Accrued other expenses	433	503
Accrued expenses and other current liabilities	$ 5,726	$ 6,380

Common Stock and Stock Option44

Common Stock and Stock Option Plan - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		12 Months Ended
	May 31, 2015	Feb. 28, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Mar. 04, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Proceeds from issuance of common stock				$ 45,438	$ 94,148
Stock options awarded			1,538,775
Weighted-average grant date fair value of stock options granted			$ 4.60	$ 9.67	$ 9.62
Unrecognized compensation cost related to stock option grants			$ 13,600
Intrinsic value of stock options exercised			200	$ 400	$ 3,200
Cash received from stock option exercises			$ 400
Stock option plan, reserved shares of common stock for future issuance			284,620
Restricted common stock, shares fully-vested			10,000
Restricted common stock outstanding expected to vest			10,000
Restricted common stock outstanding expected to vest			10,000
Unrecognized compensation cost related to restricted common stock			$ 200	$ 400
IPO [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock shares issued	2,750,000	6,900,000
Sale of stock price per share	$ 17.75	$ 15
Proceeds from issuance of common stock	$ 45,400	$ 92,700
Underwriting discounts and commissions	2,900	7,200
Other offering costs	$ 400	$ 3,500
2014 Stock Option Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum number of common stock shares granted			1,900,000
Stock option plan, vested rate			25.00%
Stock option plan, vesting period			36 months
Stock option plan, expiration period			10 years
Stock option plan, percentage of outstanding common stock			4.00%
Stock option plan, increased percentage of outstanding common stock			5.00%
Inducement Grants [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options awarded				450,700	470,272
2016 Inducement Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum number of common stock shares granted						250,000
Stock options awarded			0
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost related to stock option grants, recognition period			2 years
Unvested Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted common stock, shares issued					44,000
Restricted common stock, fair value of shares issued					$ 700
Restricted common stock, shares fully-vested					4,000
Total fair value of restricted stock awards vested			$ 100	$ 200	$ 100

Common Stock and Stock Option45

Common Stock and Stock Option Plan - Assumptions for Estimating Fair Value of Options Granted Using Black-Scholes Option Pricing Model (Detail) - Employee Stock Option [Member]	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected dividend yield	0.00%	0.00%	0.00%
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected option term (in years)	5 years 6 months	5 years 6 months	5 years 6 months
Expected volatility	71.00%	67.00%	64.00%
Risk-free interest rate	1.20%	1.50%	1.70%
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected option term (in years)	6 years 3 months 18 days	6 years 3 months 18 days	6 years 3 months 18 days
Expected volatility	79.00%	71.00%	65.00%
Risk-free interest rate	2.00%	1.90%	2.00%

Common Stock and Stock Option46

Common Stock and Stock Option Plan - Summary of Stock Option Activity for Employee and Nonemployee Awards (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
NUMBER OF OPTIONS
Outstanding at beginning of year	4,399,425
Granted	1,538,775
Exercised	(115,699)
Forfeited/Canceled	(723,052)
Outstanding at end of year	5,099,449	4,399,425
Exercisable at end of year	2,811,975
Vested and expected to vest at end of year	5,001,694
WEIGHTED- AVERAGE PRICE PER SHARE
Outstanding at beginning of year	$ 12.24
Granted	7.08
Exercised	3.42
Forfeited/Canceled	12.80
Outstanding at end of year	10.80	$ 12.24
Exercisable at end of year	11.57
Vested and expected to vest at end of year	$ 10.85
WEIGHTED- AVERAGE REMAINING CONTRACTUAL TERM (YEARS)
Outstanding at beginning of year	7 years 10 months 24 days	8 years 1 month 6 days
Exercisable at end of year	7 years 4 months 24 days
Vested and expected to vest at end of year	7 years 10 months 24 days

Common Stock and Stock Option47

Common Stock and Stock Option Plan - Summary of Restricted Common Stock Activity (Detail)	12 Months Ended
	Dec. 31, 2016$ / sharesshares
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Nonvested balance at beginning of year | shares	30,000
Vested | shares	(10,000)
Nonvested balance at end of year | shares	20,000
WEIGHTED- AVERAGE GRANT DATE FAIR VALUE PER SHARE
Nonvested balance at beginning of year | $ / shares	$ 16.30
Vested | $ / shares	16.30
Nonvested balance at end of year | $ / shares	$ 16.30

Common Stock and Stock Option48

Common Stock and Stock Option Plan - Classification of Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation	$ 9,165	$ 9,732	$ 8,237
Research and Development Expenses [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation	4,467	4,202	4,183
General and Administrative Expenses [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation	$ 4,698	$ 5,530	$ 4,054

Common Stock and Stock Option49

Common Stock and Stock Option Plan - Summary of Common Stock Warrants Outstanding (Detail)	12 Months Ended
	Dec. 31, 2016$ / sharesshares
Class of Warrant or Right [Line Items]
Number of Warrants	87,901
Exercise Price 250.00 [Member]
Class of Warrant or Right [Line Items]
Exercise Price | $ / shares	$ 250
Number of Warrants	2,198
Remaining Life (Years)	3 years 5 months 16 days
Exercise Price 7.00 [Member]
Class of Warrant or Right [Line Items]
Exercise Price | $ / shares	$ 7
Number of Warrants	85,703
Remaining Life (Years)	1 year 5 months 23 days

Revenue - Additional Informatio

Revenue - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended	6 Months Ended	12 Months Ended
	Aug. 31, 2016	Sep. 30, 2015	Dec. 31, 2016	Dec. 31, 2015
NIH [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Funds available under revenue recognition grant		$ 0.2
Revenue associated with NIH grant award			$ 0.3	$ 0.2
Additional funds available for second phase of grant	$ 2
Committed funding under the revenue recognition grant	$ 1
KHK Agreement [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cash payment received			17.5
KHK Agreement [Member] | Maximum [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Regulatory, clinical and commercialization milestone payments, and royalties on net sales entitled to receive			$ 110

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Assets Measured or Disclosed at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Held-to-maturity investments
U.S. treasury securities	$ 25,004
Restricted cash equivalents
Total	38,973	$ 85,177
Money Market Fund [Member]
Cash equivalents
Money market fund	12,853	45,557
Restricted cash equivalents
Restricted investments, at fair value	1,116	1,116
US Treasury Securities [Member]
Held-to-maturity investments
U.S. treasury securities	25,004	38,504
Level 1 [Member]
Restricted cash equivalents
Total	12,853	45,557
Level 1 [Member] | Money Market Fund [Member]
Cash equivalents
Money market fund	12,853	45,557
Level 2 [Member]
Restricted cash equivalents
Total	26,120	39,620
Level 2 [Member] | Money Market Fund [Member]
Restricted cash equivalents
Restricted investments, at fair value	1,116	1,116
Level 2 [Member] | US Treasury Securities [Member]
Held-to-maturity investments
U.S. treasury securities	$ 25,004	$ 38,504

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail) - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument Fair Value Carrying Value [Abstract]
Transfers between Level 1 and Level 2	$ 0	$ 0

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax [Line Items]
Current income tax expense	$ 0	$ 0
Deferred income tax expense	$ 0	0
Tax Credit Carryforward expiration Description	Expire starting in 2028 and 2023, respectively.
Unrecognized tax benefit	$ 1,210,000	1,430,000	$ 1,216,000
Unrecognized tax benefits that would affect income tax expense if recognized	1,200,000
Accrued penalties or provisions for interest	0
Federal [Member]
Income Tax [Line Items]
Deferred income tax expense	0	$ 0
Net operating loss carryforwards	89,700,000
Tax credits	$ 2,400,000
Tax Credit Carryforward expiration Description	2,028
State [Member]
Income Tax [Line Items]
Net operating loss carryforwards	$ 77,900,000
MASSACHUSETTS
Income Tax [Line Items]
Tax credits	$ 1,600,000
Tax Credit Carryforward expiration Description	2,023

Income Taxes - Reconciliation B

Income Taxes - Reconciliation Between Income Taxes Computed at the Federal Statutory Income Tax Rate and the Provision for Benefit from Income Taxes (Detail)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Federal statutory rate	34.00%	34.00%	34.00%
Effect of:
Impact of foreign rate differential	(31.40%)	(12.60%)
Change in valuation allowance		(24.40%)	(32.00%)
Research and development tax credit	(0.70%)	0.90%	0.80%
Stock-based compensation	(0.90%)	(0.90%)	(2.60%)
Other	(1.00%)	3.00%	(0.20%)
Total	0.00%	0.00%	0.00%

Income Taxes - Deferred Tax Ass

Income Taxes - Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Net operating loss carryforwards	$ 36,727	$ 37,017
Capitalized research and development costs	1,044	2,431
Research and development credit carryforwards	2,982	3,510
Stock compensation	7,298	5,369
Depreciation and other costs	(77)	(74)
Net deferred tax assets	47,974	48,253
Valuation allowance	(47,974)	(48,253)
Net deferred tax assets	$ 0	$ 0

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of the Gross Unrecognized Tax Benefit (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Unrecognized tax benefits at the beginning of the period	$ 1,430	$ 1,216
Additions for current tax positions		421
Changes for previous tax positions	(220)	(207)
Unrecognized tax benefits at the end of the period	$ 1,210	$ 1,430

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail)	Jul. 11, 2014USD ($)	Dec. 31, 2016USD ($)Payments	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2016USD ($)	Dec. 01, 2014USD ($)
Loss Contingencies [Line Items]
Operating lease minimum payments		$ 1,581,000			$ 1,581,000	$ 1,581,000	$ 1,581,000
Rent expense		1,600,000	$ 1,700,000	$ 700,000
Research and development expense		$ 41,694,000	43,971,000	29,453,000
Cambridge Massachusetts , 2014 Operating Lease Agreement [Member]
Loss Contingencies [Line Items]
Operating lease minimum payments	$ 9,500,000
Operating lease minimum payments term	6 years
Letter of credit								$ 1,100,000
Deferred rent obligation	Dec. 1, 2014
City of Hope License Agreement [Member]
Loss Contingencies [Line Items]
License agreement date		Sep. 30, 2007
Expenses related to license agreement		$ 0	0				$ 5,000,000
Termination of license agreement description		The Company may terminate the license agreement at any time upon 90 days written notice
Research and development expense		$ 100,000	100,000	100,000
City of Hope License Agreement [Member] | Minimum [Member]
Loss Contingencies [Line Items]
Expenses related to license agreement		5,000,000
City of Hope License Agreement [Member] | Maximum [Member]
Loss Contingencies [Line Items]
Expenses related to license agreement		$ 10,000,000
Plant Bioscience Limited License Agreement [Member]
Loss Contingencies [Line Items]
License agreement date		Sep. 30, 2013
Expenses related to license agreement					$ 200,000
Research and development expense		$ 0	0	100,000
Payments on commencement of clinical trial				100,000
Carnegie Institution of Washington License Agreement [Member]
Loss Contingencies [Line Items]
Expenses related to license agreement						$ 300,000
Research and development expense		30,000	$ 30,000	$ 30,000
Additional milestone payments		$ 100,000
Number of additional milestone payments | Payments		2

Commitments and Contingencies58

Commitments and Contingencies - Summary of Future Minimum Lease Payments Payable (Detail) $ in Thousands	Dec. 31, 2016USD ($)
Commitments and Contingencies Disclosure [Abstract]
2,017	$ 1,582
2,018	1,629
2,019	1,678
2,020	1,581
Total	$ 6,470

Litigation - Additional Informa

Litigation - Additional Information (Detail) - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Outstanding litigation liabilities	$ 0	$ 0

Quarterly Financial Data (Detai

Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 133	$ 162					$ 184		$ 295	$ 184
Net loss	(14,022)	(14,176)	$ (15,622)	$ (15,693)	$ (15,635)	$ (16,944)	(16,176)	$ (14,084)	(59,513)	(62,839)	$ (47,939)
Net loss attributable to common stockholders	$ (14,022)	$ (14,176)	$ (15,622)	$ (15,693)	$ (15,635)	$ (16,944)	$ (16,176)	$ (14,084)	$ (59,513)	$ (62,839)	$ (48,143)
Net loss per share attributable to common stockholders-basic and diluted	$ (0.68)	$ (0.68)	$ (0.75)	$ (0.76)	$ (0.76)	$ (0.82)	$ (0.86)	$ (0.79)	$ (2.87)	$ (3.09)	$ (3)

Subsequent Event - Additional I

Subsequent Event - Additional Information (Detail) - Redeemable Convertible Preferred Stock [Member] $ / shares in Units, $ in Millions	Mar. 30, 2017USD ($)Days$ / sharesshares	Mar. 28, 2017Director	Dec. 31, 2016
Subsequent Event [Line Items]
Redeemable convertible preferred stock, terms of conversion			The Company’s ability to require conversion shall be subject to (i) a 19.99% blocker provision to comply with NASDAQ Listing Rules (19.99% Conversion Blocker), (ii) if so elected by an investor, a 9.99% blocker provision (9.99% Conversion Blocker) that will prohibit beneficial ownership of more than 9.99% of the outstanding shares of the Company’s common stock or voting power at any time, and (iii) applicable regulatory restrictions.
Subsequent Event [Member]
Subsequent Event [Line Items]
Redeemable convertible preferred stock, issued | shares	700,000
Redeemable convertible preferred stock, par value	$ 0.0001
Redeemable convertible preferred stock, price per share	$ 100
Proceeds from private placement | $	$ 70
Cumulative dividends rate	12.00%
Liquidation preference percentage	101.00%
Percentage of rate reduction	4.00%
Number of interest rate reductions	2
Initial conversion price	$ 3.19
Percentage of redeemable convertible preferred stock conversion blocker provision	19.99%
Percentage of redeemable convertible preferred stock ownership limit conversion blocker provision	9.99%
Conversion price percentage of company's common stock	200.00%
Number of trading days | Days	45
Number of consecutive trading days applicable conversion price	60 days
Maximum net borrowings under debt covenant | $	$ 10
Existing number of directors | Director		8
Increased number of directors | Director		9
Subsequent Event [Member] | Director [Member]
Subsequent Event [Line Items]
Minimum required ownership percentage		25.00%