Dicerna Pharmaceuticals (DRNA) 10-Q 10 Nov 15 2015 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2015	Nov. 10, 2015
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2015
Document Fiscal Year Focus	2,015
Document Fiscal Period Focus	Q3
Trading Symbol	DRNA
Entity Registrant Name	DICERNA PHARMACEUTICALS INC
Entity Central Index Key	1,399,529
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		20,593,117

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
CURRENT ASSETS:
Cash and cash equivalents	$ 52,943	$ 26,067
Held-to-maturity investments	41,096	70,055
Prepaid expenses and other current assets	1,670	1,194
Total current assets	95,709	97,316
NONCURRENT ASSETS:
Held-to-maturity investments	13,990	2,501
Property and equipment-net	2,715	2,165
Assets held in restriction	1,116	1,380
Other noncurrent assets	111	243
Total noncurrent assets	17,932	6,289
TOTAL ASSETS	113,641	103,605
CURRENT LIABILITIES:
Accounts payable	1,370	1,237
Accrued expenses and other current liabilities	7,991	3,845
Deferred rent		77
Total current liabilities	9,361	5,159
NONCURRENT LIABILITIES:
Security deposit		106
Total noncurrent liabilities		106
TOTAL LIABILITIES	$ 9,361	$ 5,265
STOCKHOLDERS' EQUITY:
Preferred stock, $0.0001 par value-5,000,000 shares authorized, no shares issued and outstanding at September 30, 2015 and December 31, 2014
Common stock, $0.0001 par value-150,000,000 shares authorized at September 30, 2015 and December 31, 2014; 20,593,117 shares and 17,786,867 shares issued and outstanding at September 30, 2015 and December 31, 2014, respectively	$ 2	$ 3
Additional paid-in capital	284,886	231,741
Accumulated deficit	(180,608)	(133,404)
Total stockholders' equity	104,280	98,340
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	$ 113,641	$ 103,605

Condensed Consolidated Balance3

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2015	Dec. 31, 2014
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	20,593,117	17,786,867
Common stock, shares outstanding	20,593,117	17,786,867

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Income Statement [Abstract]
Revenues			$ 184
Operating expenses:
Research and development	$ 12,142	$ 7,489	32,708	$ 19,546
General and administrative	4,857	3,725	14,822	10,938
Total operating expenses	16,999	11,214	47,530	30,484
Loss from operations	(16,999)	(11,214)	(47,346)	(30,484)
Other income (expense):
Interest income	55	21	142	36
Interest expense				(199)
Preferred stock warrant remeasurement				(2,559)
Loss on extinguishment of debt				(143)
Total net other income (expense)	55	21	142	(2,865)
Net loss	(16,944)	(11,193)	(47,204)	(33,349)
Less: Accretion and dividends on redeemable convertible preferred stock				204
Net loss attributable to common stockholders	$ (16,944)	$ (11,193)	$ (47,204)	$ (33,553)
Net loss per share attributable to common stockholders-basic and diluted	$ (0.82)	$ (0.63)	$ (2.47)	$ (2.17)
Weighted average shares outstanding-basic and diluted	20,592,840	17,706,645	19,097,230	15,438,699

Condensed Consolidated Stateme5

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (47,204)	$ (33,349)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	529	419
Net amortization of premium/discount on investments	100
Stock-based compensation	7,374	6,224
Loss on extinguishment of debt		143
Increase in fair value of preferred stock warrant liability		2,559
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(459)	(592)
Accounts payable	133	(119)
Accrued expenses and other liabilities	3,903	2,196
Security deposit		106
Deferred rent	95	(26)
Net cash used in operating activities	(35,529)	(22,439)
CASH FLOWS FROM INVESTING ACTIVITIES:
Changes in assets held in restriction	264	(1,116)
Purchases of property and equipment	(995)	(1,010)
Maturities of held-to-maturity investments	53,500	2,495
Purchases of held-to-maturity investments	(36,130)	(82,611)
Net cash provided by (used in) investing activities	16,639	(82,242)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from stock option exercises and issuances under Employee Stock Purchase Plan	403	779
Settlement of restricted stock for tax withholding	(75)
Proceeds from public offering of common stock, net of costs	45,438	94,148
Repayments of long-term debt principal		(5,026)
Net cash provided by financing activities	45,766	89,901
INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	26,876	(14,780)
CASH AND CASH EQUIVALENTS - Beginning of period	26,067	46,595
CASH AND CASH EQUIVALENTS - End of period	$ 52,943	31,815
SUPPLEMENTAL CASH FLOW INFORMATION:
Warrant conversion to common stock		$ 3,088

Description of Business and Bas

Description of Business and Basis of Presentation	9 Months Ended
	Sep. 30, 2015
Accounting Policies [Abstract]
Description of Business and Basis of Presentation	1. Description of Business and Basis of Presentation Nature of business Dicerna Pharmaceuticals, Inc. and its subsidiaries (the Company) is a biopharmaceutical company focused on the discovery and development of innovative treatments for rare inherited diseases involving the liver and for cancers that are genetically defined. The Company is using its proprietary RNA interference (RNAi) technology platform to build a broad pipeline in these therapeutic areas. The Company intends to discover, develop and commercialize novel therapeutics either on its own or in collaboration with pharmaceutical partners. The Company continues to be subject to a number of risks common to companies in similar stages of development. Principal among these risks are the uncertainties of technological innovations, which are particularly high in the field of drug discovery and development, dependence on key individuals, development of the same or similar technological innovations by the Company’s competitors and protection of proprietary technology. The Company’s ability to fund its planned preclinical and clinical operations, including completion of its clinical trials, is expected to depend on the amount and timing of cash receipts under its existing collaboration agreement, as well as any future collaboration or product sales and/or financing transactions. 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 (the IPO) at a price to the public of $15.00 per share, resulting in proceeds to the Company of $92,750 after deducting underwriting discounts and commissions of approximately $7,245 and offering expenses paid by the Company of approximately $3,506. In connection with the close of the IPO, all of the outstanding shares of Series A mandatorily redeemable, convertible preferred stock (Series A preferred stock), Series B mandatorily redeemable, convertible preferred stock (Series B preferred stock) and Series C mandatorily redeemable, convertible preferred stock (Series C preferred stock) were converted into shares of common stock on a one-for-one basis immediately prior to the closing of the IPO. 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 $45,438 after deducting underwriting discounts and commissions of approximately $2,929 and offering cost of approximately $446. Basis of presentation and consolidation The accompanying unaudited condensed consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the U.S. (GAAP) and in accordance with the rules and regulations of the Securities and Exchange Commission (SEC) for interim financial information. Accordingly, they do not include all of the information and notes required by GAAP for a complete set of financial statements. The unaudited condensed consolidated interim financial statements have been prepared on the same basis as the annual financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary to present fairly the Company’s financial position at September 30, 2015 and results of operations and cash flows for the interim periods ended September 30, 2015 and 2014. These unaudited condensed consolidated interim financial statements should be read in conjunction with the audited consolidated financial statements and notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2014. The results of the three and nine months ended September 30, 2015 are not necessarily indicative of the results to be expected for the year ending December 31, 2015 or for any other interim period or for any other future year. Summary of Significant Accounting Policies Revenue Recognition Grant revenue is recognized in the period in which the related grant research and activities are incurred, provided that the conditions under which the grant was provided have been met and the Company only has perfunctory obligations outstanding. Any amounts received in advance of revenue recognition are classified as deferred revenue in the consolidated balance sheets. Costs associated with grants are included in research and development expenses in the consolidated statements of operations.

Revenue Recognition

Revenue Recognition	9 Months Ended
	Sep. 30, 2015
Text Block [Abstract]
Revenue Recognition	2. Revenue Recognition NIH Grants In April 2015, the National Cancer Institute (NCI), a division of the National Institutes of Health (NIH), awarded the Company a grant related to cancer treatment research. The project period for this grant covers a three month period which commenced in April 2015, with total funds available of approximately $184. The payment of the NIH grant award was based upon subcontractor and internal costs incurred that are specifically covered by the grant, and where applicable, a facilities and administrative rate that provides funding for overhead expenses. During the three and nine month periods ended September 30, 2015, the Company recognized $0 and $184 of revenue associated with the NIH grant award.

Net Loss Per Share Attributable

Net Loss Per Share Attributable to Common Stockholders	9 Months Ended
	Sep. 30, 2015
Earnings Per Share [Abstract]
Net Loss Per Share Attributable to Common Stockholders	3. Net Loss Per Share Attributable to Common Stockholders The following table summarizes the computation of basic and diluted net loss per share attributable to common stockholders of the Company (in thousands, except share and per share data): Three Months Ended September 30, Nine Months Ended September 30, 2015 2014 2015 2014 Net loss $ (16,944 ) $ (11,193 ) $ (47,204 ) $ (33,349 ) Less: Accretion and dividends on redeemable convertible preferred stock — — — 204 Net loss attributable to common stockholders (16,944 ) (11,193 ) (47,204 ) (33,553 ) Net loss per share attributable to common stockholders—basic and diluted $ (0.82 ) $ (0.63 ) $ (2.47 ) $ (2.17 ) Weighted average shares outstanding—basic and diluted 20,592,840 17,706,645 19,097,230 15,438,699 The following potentially dilutive securities outstanding during the period, prior to the use of the treasury stock method or if-converted method, have been excluded from the computation of diluted weighted-average common stock outstanding, because such securities had an anti-dilutive impact since the Company has a net loss attributable to common stockholders: Three Months Ended September 30, Nine Months Ended September 30, 2015 2014 2015 2014 Options to purchase common stock 4,373,594 3,323,387 4,236,529 2,560,239 Warrants to purchase common stock 87,901 87,901 87,901 78,302 Warrants to purchase redeemable convertible preferred stock — — — 17,064 Redeemable convertible preferred stock — — — 1,357,621 Unvested restricted stock 63,637 104,485 73,449 94,275

Held-to-maturity investments

Held-to-maturity investments	9 Months Ended
	Sep. 30, 2015
Text Block [Abstract]
Held-to-maturity investments	4. Held-to-maturity investments 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 such designation as of each balance sheet date. Debt securities carried at amortized cost are classified as held-to-maturity when the Company has the positive intent and ability to hold the securities to maturity. The following tables provide information relating to held-to-maturity investments: At September 30, 2015: Amortized Gross Gross Fair Held-to-maturity investments U.S. Government treasury $ 55,086 $ 33 $ — 55,119 Total held-to-maturity investments $ 55,086 $ 33 $ — 55,119 At December 31, 2014: Amortized Gross Gross Fair Held-to-maturity investments U.S. Government treasury and agency securities $ 72,556 $ 2 $ (26 ) $ 72,532 Total held-to-maturity investments $ 72,556 $ 2 $ (26 ) $ 72,532 The amortized cost and fair value of held-to-maturity investments by contractual maturities at September 30, 2015, are as follows (in thousands): Held-to-Maturity Amortized Fair Maturing in one year or less $ 41,096 $ 41,112 Maturing after one year through two years 13,990 14,007 Total $ 55,086 $ 55,119

Long-term Debt

Long-term Debt	9 Months Ended
	Sep. 30, 2015
Debt Disclosure [Abstract]
Long-term Debt	5. Long-term Debt On March 26, 2009, the Company entered into a loan and security agreement with an independent finance company, Hercules Technology II, LP (Hercules), for up to $7,000 (Hercules loan). The Hercules loan, which has since been repaid, was collateralized by a security interest in all tangible assets. On June 28, 2011, the Company and Hercules executed a second amendment to the loan and security agreement, which increased the maximum loan amount to $12,000. Upon execution of the second amendment, the Company drew a $7,000 advance, a portion of which the Company used to repay the outstanding balance of principal and interest under the original loan and security agreement. On December 15, 2011, the Company drew down the remaining $5,000. Interest was payable monthly and principal was to be repaid in equal monthly installments beginning April 1, 2012 through January 2, 2015. The applicable annual interest rate was 10.15% at December 31, 2013. On April 7, 2014, the Company repaid the remaining amount of the Hercules loan in full in a total amount of $3,590. In connection with the Hercules loan, the Company issued warrants to Hercules for the purchase of an aggregate of 21,000 shares of Series A preferred stock and 26,400 shares of Series B preferred stock each at an exercise price of $25.00 per share. Immediately prior to the closing of the IPO on February 4, 2014, all of the outstanding shares of Series A, Series B and Series C preferred stock were automatically converted into shares of common stock on a one-for-one basis. The fair value of the warrants was classified as a liability in the balance sheet as of December 31, 2013. After the conversion of Series A and Series B preferred stock, the fair value of the warrants was reclassified as a part of stockholders’ equity. The remeasurement of the liability continued until the date of the closing of the IPO. The fair value of the outstanding Hercules warrants as of the IPO closing date was $765 and was determined using the Black-Scholes option-pricing model with the following assumptions: February 4, Stock price $ 32.66 Expected option term (in years) 3.00 Expected volatility 62 % Risk-free interest rate 0.69 % Expected dividend yield 0.00 % On February 11, 2014, Hercules net exercised the warrants in exchange for a total of 12,702 shares of common stock. There were no Series A and Series B warrants outstanding at September 30, 2015 and December 31, 2014. The adjustment to this preferred stock warrant liability related to the Hercules warrants was recorded in other income (expense) and amounted to $0 for the three and nine month periods ended September 30, 2015 compared to $0 and $(671) for the same periods in the prior year.

Stock-Based Compensation

Stock-Based Compensation	9 Months Ended
	Sep. 30, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-Based Compensation	6. Stock-Based Compensation Stock options granted to nonemployees Stock-based compensation expense related to stock options granted to nonemployees is recognized as the consulting services are rendered, generally on a straight-line basis. The Company believes that the fair value of the stock options is more reliably measurable than the fair value of the services received. Compensation expense is subject to re-measurement until the options vest. In September 2013, the Company granted stock options to purchase 132,500 shares of common stock to nonemployees with an initial fair value of $337. Based on the terms of the nonemployee stock option agreements the Company recorded nonemployee stock-based compensation of $37 and $192 for the three and nine month periods ended September 30, 2015, as compared to $117 and $1,777 in the comparable 2014 periods. The assumptions used to estimate fair value were as follows: Three Months Ended Nine Months Ended Stock price $8.21 – $12.22 $8.21 – $24.43 Expected option term (in years) 4.59 – 4.75 4.37 – 5.29 Expected volatility 66% – 72% 66% – 72% Risk-free interest rate 1.27% – 1.47% 1.21% – 1.57% Expected dividend yield 0.00% 0.00% Three Months Ended Nine Months Ended Stock price $12.73 – $15.02 $12.73 – $41.12 Expected option term (in years) 5.73 – 5.98 0.25 – 6.86 Expected volatility 63% – 65% 56% – 65% Risk-free interest rate 1.75% – 1.92% 0.08% – 2.29% Expected dividend yield 0.00% 0.00% As of September 30, 2015, there were 30,625 unvested stock options held by nonemployees. Stock option grants to employees During the three and nine month periods ended September 30, 2015, the Company granted stock options to purchase 195,700 and 1,045,626 shares of common stock to employees with grant date fair values of $1,034 and $10,338, respectively, compared to 240,500 and 2,051,306 shares with grant date fair values of $712 and $20,215, for the three and nine month periods in 2014. Employee stock-based compensation for the three and nine month periods ended September 30, 2015 were $2,356 and $7,182 as compared to $1,490 and $4,447, respectively, for the comparable 2014 periods. The assumptions used to estimate the grant date fair value for 2015 grants were as follows: Three Months Ended Nine Months Ended Stock price $8.21 $8.21 – $24.03 Expected option term (in years) 6.25 5.50 – 6.25 Expected volatility 71% 67% – 71% Risk-free interest rate 1.54% 1.51% – 1.81% Expected dividend yield 0.00% 0.00% Three Months Ended Nine Months Ended Stock price $13.32 – $14.27 $13.32 – $19.83 Expected option term (in years) 6.25 5.50 – 6.25 Expected volatility 65% 64% – 65% Risk-free interest rate 1.85% – 2.02% 1.79% – 2.02% Expected dividend yield 0.00% 0.00%

Redeemable Convertible Preferre

Redeemable Convertible Preferred Stock	9 Months Ended
	Sep. 30, 2015
Text Block [Abstract]
Redeemable Convertible Preferred Stock	7. Redeemable Convertible Preferred Stock The consummation of the IPO on February 4, 2014 resulted in the conversion of all of the shares of the Company’s Series A, Series B and Series C preferred stock into shares of common stock. Each share of Series A, Series B and Series C preferred stock was automatically converted into common stock on a one-for-one basis. The conversion of Series A, Series B and Series C preferred stock resulted in the issuance of 10,589,434 shares of common stock. After the conversion of Series C preferred stock, the fair value of the warrants related to Series C preferred stock outstanding immediately prior to the closing of the IPO was reclassified as a part of stockholders’ equity. The remeasurement of the Series C preferred stock warrant liability continued until the closing date of the IPO. The fair value of the Series C preferred stock warrants as of the IPO closing date was $2,323 and was determined using the Black-Scholes option-pricing model with the following assumptions: February 4, Stock price $ 32.66 Expected option term (in years) 4.39 Expected volatility 65 % Risk-free interest rate 1.52 % Expected dividend yield 0.00 % The adjustment to the Series C preferred stock warrant liability was recorded in other income (expense) and amounted to $0 for the three and nine month periods ended September 30, 2015, compared to $0 and ($1,888) for the same periods in 2014.

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2015
Fair Value Disclosures [Abstract]
Fair Value Measurements	8. 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. 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. This hierarchy requires the Company to use observable market data, when available, and to minimize the use of unobservable inputs when determining fair value. A summary of the Company’s assets that are measured or disclosed at fair value as of September 30, 2015 and December 31, 2014 are presented below: Description At September 30, Level 1 Level 2 Level 3 Cash equivalents Money market fund $ 43,942 $ 43,942 $ — $ — Held-to-maturity investments U.S. treasury securities 55,119 — 55,119 — Assets held in restriction Money market fund 1,116 — 1,116 — Total $ 100,177 $ 43,942 $ 56,235 $ — Description At December 31, Level 1 Level 2 Level 3 Cash equivalents Money market fund $ 20,425 $ 20,425 $ — $ — Held-to-maturity investments U.S. treasury securities and government agency bonds 72,532 — 72,532 — Assets held in restriction Money market fund and certificate of deposit 1,380 — 1,380 — Total $ 94,337 $ 20,425 $ 73,912 $ — The Company’s cash equivalents, primarily money market accounts are classified within Level 1 of the fair value hierarchy because they are valued using quoted prices as of September 30, 2015 and December 31, 2014, respectively. The Company’s assets held in restriction 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 and the 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 September 30, 2015 and December 31, 2014, respectively. The Company’s held-to-maturity investments bore interest at the prevailing market rates for instruments with similar characteristics. The 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 September 30, 2015 and December 31, 2014, respectively. For the three and nine month periods ended September 30, 2015 and 2014, there were no transfers between Level 1 and Level 2. The fair value of the preferred stock warrant liability was determined using the Black-Scholes option-pricing model until the IPO conversion date of February 4, 2014. After the closing of the IPO, the remaining preferred stock warrant liability was no longer subject to remeasurement as the warrants to purchase the Company’s preferred stock became warrants to purchase shares of the Company’s common stock. As of the IPO closing date, the fair value of the preferred stock warrants was based significantly on the fair value of the Company’s publicly traded common stock and other observable inputs and was reclassified to Level 2. The fair value of the preferred stock warrant prior to the closing of the IPO was based significantly on the fair value of the preferred stock, which was developed using unobservable inputs, and was classified within Level 3. The following table provides a roll-forward of the Company’s liabilities measured at fair value on a recurring basis using unobservable inputs (Level 3): BALANCE—January 1, 2014 $ 529 Change in fair value of warrant liability 2,559 Transfers to Level 2 (3,088 ) BALANCE— September 30, 2014 $ — There were no preferred stock warrants outstanding as of September 30, 2015 and December 31, 2014.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2015
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	9. Commitments and Contingencies Facility lease On July 11, 2014, the Company executed a non-cancelable operating lease for office and laboratory space in Cambridge, Massachusetts. The lease agreement obligates the Company to future minimum payments totaling $9,498 over a six-year lease term. The lease commenced on December 1, 2014. As part of the lease agreement, the Company established a $1,116 letter of credit, secured by a money market account which is included in assets held in restriction at September 30, 2015 and December 31, 2014. On April 9, 2015, the Company terminated its lease and sub-lease at 480 Arsenal Street in Watertown. The transactions did not have a material impact on the Company’s financial statements. The associated letter of credit was cancelled by the bank during the second quarter of 2015, and a $264 certificate of deposit that secured the letter of credit was redeemed and transferred to cash and cash equivalents. 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 (the Medical Center). In consideration for the right to develop, manufacture, and commercialize products based on certain of the Medical Center’s intellectual property, the Company paid a one-time, non-refundable license fee and issued shares of common stock as consideration for the license. The Company is required to pay an annual license maintenance fee, reimburse the Medical Center for patent costs incurred, and pay an amount within the range of $5,000 to $10,000 upon the achievement of certain milestones, and royalties on future sales, if any. 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 the Medical Center. There were no expenses related to milestones or royalties under this agreement for the three and nine month periods ended September 30, 2015 and the comparable prior year periods. 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 has granted to the Company a license to certain of its U.S. patents and patent applications to research, discover, develop, manufacture, sell, import and export, products incorporating one or more short RNA molecules (SRMs). The Company has paid PBL a one-time, non-refundable signature fee and will pay PBL a nomination fee for any additional SRMs nominated by the Company under the agreement. The Company is further obligated to pay PBL milestone payments upon achievement of certain clinical and regulatory milestones. During 2014, the Company paid $100 to PBL based on meeting a clinical milestone. In addition, PBL is entitled to receive royalties of any net sale revenue of any licensed product candidates sold by the Company. Research and development expense related to this agreement for the nine month period ended September 30, 2015 was $0 as compared to $100 in the comparable 2014 period. Arbutus Biopharma Corporation license agreement In November 2014, the Company signed a licensing and collaboration agreement with Arbutus Biopharma Corporation (formerly, Tekmira Pharmaceuticals Corporation) (Arbutus) to license Arbutus’ LNP delivery technology for exclusive use in the Company’s primary hyperoxaluria type 1 (PH1) development program. The Company will use Arbutus’ LNP technology to deliver DCR-PH1, for the treatment of PH1. As of September 30, 2015, the Company had paid $3,000 in cumulative license fees. Arbutus is entitled to receive additional payments of $22,000 in aggregate development milestones, plus a mid-single-digit royalty on future PH1 sales. This partnership also includes a supply agreement with Arbutus providing clinical drug supply and regulatory support.

Litigation

Litigation	9 Months Ended
	Sep. 30, 2015
Commitments and Contingencies Disclosure [Abstract]
Litigation	10. 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 Sirna Therapeutics, Inc. (Sirna), which at the time was a subsidiary of Merck & Co., Inc., and in connection with our discussions with Merck to acquire Sirna, which was subsequently acquired by Alnylam. The complaint seeks, among other things, 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 September 30, 2015 and December 31, 2014.

Description of Business and B16

Description of Business and Basis of Presentation (Policies)	9 Months Ended
	Sep. 30, 2015
Accounting Policies [Abstract]
Nature of business	Nature of business Dicerna Pharmaceuticals, Inc. and its subsidiaries (the Company) is a biopharmaceutical company focused on the discovery and development of innovative treatments for rare inherited diseases involving the liver and for cancers that are genetically defined. The Company is using its proprietary RNA interference (RNAi) technology platform to build a broad pipeline in these therapeutic areas. The Company intends to discover, develop and commercialize novel therapeutics either on its own or in collaboration with pharmaceutical partners. The Company continues to be subject to a number of risks common to companies in similar stages of development. Principal among these risks are the uncertainties of technological innovations, which are particularly high in the field of drug discovery and development, dependence on key individuals, development of the same or similar technological innovations by the Company’s competitors and protection of proprietary technology. The Company’s ability to fund its planned preclinical and clinical operations, including completion of its clinical trials, is expected to depend on the amount and timing of cash receipts under its existing collaboration agreement, as well as any future collaboration or product sales and/or financing transactions. 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 (the IPO) at a price to the public of $15.00 per share, resulting in proceeds to the Company of $92,750 after deducting underwriting discounts and commissions of approximately $7,245 and offering expenses paid by the Company of approximately $3,506. In connection with the close of the IPO, all of the outstanding shares of Series A mandatorily redeemable, convertible preferred stock (Series A preferred stock), Series B mandatorily redeemable, convertible preferred stock (Series B preferred stock) and Series C mandatorily redeemable, convertible preferred stock (Series C preferred stock) were converted into shares of common stock on a one-for-one basis immediately prior to the closing of the IPO. 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 $45,438 after deducting underwriting discounts and commissions of approximately $2,929 and offering cost of approximately $446.
Basis of presentation and consolidation	Basis of presentation and consolidation The accompanying unaudited condensed consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the U.S. (GAAP) and in accordance with the rules and regulations of the Securities and Exchange Commission (SEC) for interim financial information. Accordingly, they do not include all of the information and notes required by GAAP for a complete set of financial statements. The unaudited condensed consolidated interim financial statements have been prepared on the same basis as the annual financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary to present fairly the Company’s financial position at September 30, 2015 and results of operations and cash flows for the interim periods ended September 30, 2015 and 2014. These unaudited condensed consolidated interim financial statements should be read in conjunction with the audited consolidated financial statements and notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2014. The results of the three and nine months ended September 30, 2015 are not necessarily indicative of the results to be expected for the year ending December 31, 2015 or for any other interim period or for any other future year.
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies
Revenue Recognition	Revenue Recognition Grant revenue is recognized in the period in which the related grant research and activities are incurred, provided that the conditions under which the grant was provided have been met and the Company only has perfunctory obligations outstanding. Any amounts received in advance of revenue recognition are classified as deferred revenue in the consolidated balance sheets. Costs associated with grants are included in research and development expenses in the consolidated statements of operations.

Net Loss Per Share Attributab17

Net Loss Per Share Attributable to Common Stockholders (Tables)	9 Months Ended
	Sep. 30, 2015
Earnings Per Share [Abstract]
Summary of Computation of Basic and Diluted Net Loss Per Share Attributable to Common Stockholders	The following table summarizes the computation of basic and diluted net loss per share attributable to common stockholders of the Company (in thousands, except share and per share data): Three Months Ended September 30, Nine Months Ended September 30, 2015 2014 2015 2014 Net loss $ (16,944 ) $ (11,193 ) $ (47,204 ) $ (33,349 ) Less: Accretion and dividends on redeemable convertible preferred stock — — — 204 Net loss attributable to common stockholders (16,944 ) (11,193 ) (47,204 ) (33,553 ) Net loss per share attributable to common stockholders—basic and diluted $ (0.82 ) $ (0.63 ) $ (2.47 ) $ (2.17 ) Weighted average shares outstanding—basic and diluted 20,592,840 17,706,645 19,097,230 15,438,699
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 method, have been excluded from the computation of diluted weighted-average common stock outstanding, because such securities had an anti-dilutive impact since the Company has a net loss attributable to common stockholders: Three Months Ended September 30, Nine Months Ended September 30, 2015 2014 2015 2014 Options to purchase common stock 4,373,594 3,323,387 4,236,529 2,560,239 Warrants to purchase common stock 87,901 87,901 87,901 78,302 Warrants to purchase redeemable convertible preferred stock — — — 17,064 Redeemable convertible preferred stock — — — 1,357,621 Unvested restricted stock 63,637 104,485 73,449 94,275

Held-to-maturity investments (T

Held-to-maturity investments (Tables)	9 Months Ended
	Sep. 30, 2015
Text Block [Abstract]
Schedule of Held-To-Maturity Investments	The following tables provide information relating to held-to-maturity investments: At September 30, 2015: Amortized Gross Gross Fair Held-to-maturity investments U.S. Government treasury $ 55,086 $ 33 $ — 55,119 Total held-to-maturity investments $ 55,086 $ 33 $ — 55,119 At December 31, 2014: Amortized Gross Gross Fair Held-to-maturity investments U.S. Government treasury and agency securities $ 72,556 $ 2 $ (26 ) $ 72,532 Total held-to-maturity investments $ 72,556 $ 2 $ (26 ) $ 72,532
Amortized Cost and Fair Value of Held-To-Maturity Investments	The amortized cost and fair value of held-to-maturity investments by contractual maturities at September 30, 2015, are as follows (in thousands): Held-to-Maturity Amortized Fair Maturing in one year or less $ 41,096 $ 41,112 Maturing after one year through two years 13,990 14,007 Total $ 55,086 $ 55,119

Long-term Debt (Tables)

Long-term Debt (Tables)	9 Months Ended
	Sep. 30, 2015
Debt Disclosure [Abstract]
Summary of Estimated Fair Values of Outstanding Warrants Using Black-Scholes Option-Pricing Model	The fair value of the outstanding Hercules warrants as of the IPO closing date was $765 and was determined using the Black-Scholes option-pricing model with the following assumptions: February 4, Stock price $ 32.66 Expected option term (in years) 3.00 Expected volatility 62 % Risk-free interest rate 0.69 % Expected dividend yield 0.00 %

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2015
Stock Options Granted to Nonemployees [Member]
Schedule of Valuation Assumptions	The assumptions used to estimate fair value were as follows: Three Months Ended Nine Months Ended Stock price $8.21 – $12.22 $8.21 – $24.43 Expected option term (in years) 4.59 – 4.75 4.37 – 5.29 Expected volatility 66% – 72% 66% – 72% Risk-free interest rate 1.27% – 1.47% 1.21% – 1.57% Expected dividend yield 0.00% 0.00% Three Months Ended Nine Months Ended Stock price $12.73 – $15.02 $12.73 – $41.12 Expected option term (in years) 5.73 – 5.98 0.25 – 6.86 Expected volatility 63% – 65% 56% – 65% Risk-free interest rate 1.75% – 1.92% 0.08% – 2.29% Expected dividend yield 0.00% 0.00%
Employee Stock Option [Member]
Schedule of Valuation Assumptions	The assumptions used to estimate the grant date fair value for 2015 grants were as follows: Three Months Ended Nine Months Ended Stock price $8.21 $8.21 – $24.03 Expected option term (in years) 6.25 5.50 – 6.25 Expected volatility 71% 67% – 71% Risk-free interest rate 1.54% 1.51% – 1.81% Expected dividend yield 0.00% 0.00% Three Months Ended Nine Months Ended Stock price $13.32 – $14.27 $13.32 – $19.83 Expected option term (in years) 6.25 5.50 – 6.25 Expected volatility 65% 64% – 65% Risk-free interest rate 1.85% – 2.02% 1.79% – 2.02% Expected dividend yield 0.00% 0.00%

Redeemable Convertible Prefer21

Redeemable Convertible Preferred Stock (Tables)	9 Months Ended
	Sep. 30, 2015
Series C Redeemable Convertible Preferred Stock [Member]
Summary of Estimated Fair Values of Outstanding Warrants Using Black-Scholes Option-Pricing Model	The fair value of the Series C preferred stock warrants as of the IPO closing date was $2,323 and was determined using the Black-Scholes option-pricing model with the following assumptions: February 4, Stock price $ 32.66 Expected option term (in years) 4.39 Expected volatility 65 % Risk-free interest rate 1.52 % Expected dividend yield 0.00 %

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2015
Fair Value Disclosures [Abstract]
Schedule of Assets Measured or Disclosed at Fair Value	A summary of the Company’s assets that are measured or disclosed at fair value as of September 30, 2015 and December 31, 2014 are presented below: Description At September 30, Level 1 Level 2 Level 3 Cash equivalents Money market fund $ 43,942 $ 43,942 $ — $ — Held-to-maturity investments U.S. treasury securities 55,119 — 55,119 — Assets held in restriction Money market fund 1,116 — 1,116 — Total $ 100,177 $ 43,942 $ 56,235 $ — Description At December 31, Level 1 Level 2 Level 3 Cash equivalents Money market fund $ 20,425 $ 20,425 $ — $ — Held-to-maturity investments U.S. treasury securities and government agency bonds 72,532 — 72,532 — Assets held in restriction Money market fund and certificate of deposit 1,380 — 1,380 — Total $ 94,337 $ 20,425 $ 73,912 $ —
Schedule of Roll-Forward of Company's Liabilities Measured at Fair Value on Recurring Basis Using Unobservable Inputs (Level 3)	The fair value of the preferred stock warrant prior to the closing of the IPO was based significantly on the fair value of the preferred stock, which was developed using unobservable inputs, and was classified within Level 3. The following table provides a roll-forward of the Company’s liabilities measured at fair value on a recurring basis using unobservable inputs (Level 3): BALANCE—January 1, 2014 $ 529 Change in fair value of warrant liability 2,559 Transfers to Level 2 (3,088 ) BALANCE— September 30, 2014 $ —

Description of Business and B23

Description of Business and Basis of Presentation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		9 Months Ended
	May. 31, 2015	Feb. 28, 2014	Sep. 30, 2015	Sep. 30, 2014
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Proceeds from issuance of common stock			$ 45,438	$ 94,148
Preferred stock conversion basis			In connection with the close of the IPO, all of the outstanding shares of Series A mandatorily redeemable, convertible preferred stock (Series A preferred stock), Series B mandatorily redeemable, convertible preferred stock (Series B preferred stock) and Series C mandatorily redeemable, convertible preferred stock (Series C preferred stock) were converted into shares of common stock on a one-for-one basis immediately prior to the closing of the IPO.
IPO [Member]
Organization Consolidation And Presentation Of Financial Statements [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	$ 45,438	$ 92,750
Underwriting discounts and commissions	2,929	7,245
Offering expenses		$ 3,506
Offering cost accrued	$ 446

Revenue Recognition - Additiona

Revenue Recognition - Additional Information (Detail) - National Institutes of Health [Member] - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2015
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Funds available under revenue recognition grant	$ 184
Revenue associated with NIH grant award	$ 0	$ 184

Net Loss Per Share Attributab25

Net Loss Per Share Attributable to Common Stockholders - Summary of Computation of Basic and Diluted Net Loss Per Share Attributable to Common Stockholders (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Earnings Per Share [Abstract]
Net loss	$ (16,944)	$ (11,193)	$ (47,204)	$ (33,349)
Less: Accretion and dividends on redeemable convertible preferred stock				204
Net loss attributable to common stockholders	$ (16,944)	$ (11,193)	$ (47,204)	$ (33,553)
Net loss per share attributable to common stockholders-basic and diluted	$ (0.82)	$ (0.63)	$ (2.47)	$ (2.17)
Weighted average shares outstanding-basic and diluted	20,592,840	17,706,645	19,097,230	15,438,699

Net Loss Per Share Attributab26

Net Loss Per Share Attributable to Common Stockholders - Schedule of Dilutive Securities Outstanding (Detail) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Employee Stock Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities	4,373,594	3,323,387	4,236,529	2,560,239
Hercules Warrants [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities	87,901	87,901	87,901	78,302
Warrants to Purchase Redeemable Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities				17,064
Redeemable Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities				1,357,621
Unvested Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities	63,637	104,485	73,449	94,275

Held-to-Maturity Investments -

Held-to-Maturity Investments - Schedule of Held-to-Maturity Investments (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity, Amortized Cost, Total	$ 55,086	$ 72,556
Held-to-maturity investments, Gross Unrealized Gains	33	2
Held-to-maturity investments, Gross Unrealized Losses		(26)
Held-to-maturity investments, Fair Value, Total	55,119	72,532
US Treasury Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity, Amortized Cost, Total	55,086
Held-to-maturity investments, Gross Unrealized Gains	33
Held-to-maturity investments, Fair Value, Total	$ 55,119
U.S. Government Treasury and Agency Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity, Amortized Cost, Total		72,556
Held-to-maturity investments, Gross Unrealized Gains		2
Held-to-maturity investments, Gross Unrealized Losses		(26)
Held-to-maturity investments, Fair Value, Total		$ 72,532

Held-to-Maturity-Investments -

Held-to-Maturity-Investments - Amortized Cost and Fair Value of Held-to-Maturity Investments (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Investments, Debt and Equity Securities [Abstract]
Held-to-Maturity securities, Maturing in one year or less, Amortized Cost	$ 41,096	$ 70,055
Maturing after one year through two years, Amortized Cost	13,990	2,501
Held to Maturity, Amortized Cost, Total	55,086	72,556
Held-to-Maturity securities, Maturing in one year or less, Fair Value	41,112
Maturing after one year through two years, Fair Value	14,007
Held-to-Maturity, Fair Value, Total	$ 55,119	$ 72,532

Long-term Debt - Additional Inf

Long-term Debt - Additional Information (Detail) - USD ($)

Apr. 07, 2014

Dec. 15, 2011

Jun. 28, 2011

Sep. 30, 2015

Sep. 30, 2014

Sep. 30, 2015

Sep. 30, 2014

Dec. 31, 2014

Feb. 11, 2014

Feb. 04, 2014

Dec. 31, 2013

Mar. 26, 2009

Debt Instrument [Line Items]

Estimated fair value of outstanding warrants

$ 765,000

Common stock issued, shares

20,593,117

20,593,117

17,786,867

Adjustment to preferred stock warrant liability recorded in other income (expense)

$ (2,559,000)

Hercules Warrants [Member]

Debt Instrument [Line Items]

Adjustment to preferred stock warrant liability recorded in other income (expense)

$ 0

$ 0

$ 0

$ (671,000)

Series A Warrants [Member]

Debt Instrument [Line Items]

Estimated fair value of outstanding warrants

0

0

$ 0

Series B Warrants [Member]

Debt Instrument [Line Items]

Estimated fair value of outstanding warrants

$ 0

$ 0

$ 0

Second Amendment [Member]

Debt Instrument [Line Items]

Loan drew in advance

$ 5,000,000

$ 7,000,000

Annual interest rate

10.15%

Principal monthly installments period

April 1, 2012 through January 2, 2015

Hercules Loan [Member]

Debt Instrument [Line Items]

Loan and security agreement

$ 7,000,000

Repayment of debt

$ 3,590,000

IPO closing date

Feb. 4, 2014

Common stock issued, shares

12,702

Hercules Loan [Member] | Series A Warrants [Member]

Debt Instrument [Line Items]

Warrants exercised, number of shares

21,000

21,000

Warrants exercised, exercise price

$ 25

$ 25

Hercules Loan [Member] | Series B Warrants [Member]

Debt Instrument [Line Items]

Warrants exercised, number of shares

26,400

26,400

Warrants exercised, exercise price

$ 25

$ 25

Hercules Loan [Member] | Second Amendment [Member]

Debt Instrument [Line Items]

Loan and security agreement

$ 12,000,000

Long-term Debt - Summary of Est

Long-term Debt - Summary of Estimated Fair Values of Outstanding Warrants Using Black-Scholes Option-Pricing Model (Detail) - Hercules Warrants [Member]	Feb. 04, 2014$ / shares
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Stock price	$ 32.66
Expected option term (in years)	3 years
Expected volatility	62.00%
Risk-free interest rate	0.69%
Expected dividend yield	0.00%

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense				$ 7,374	$ 6,224
Nonemployee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option, granted	132,500
Stock options, granted fair value	$ 337
Stock-based compensation expense		$ 37	$ 117	$ 192	$ 1,777
Unvested stock options		30,625		30,625
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option, granted		195,700	240,500	1,045,626	2,051,306
Stock-based compensation expense		$ 2,356	$ 1,490	$ 7,182	$ 4,447
Fair value of stock options		$ 1,034	$ 712	$ 10,338	$ 20,215

Stock-Based Compensation - Sche

Stock-Based Compensation - Schedule of Valuation Assumptions (Detail) - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Nonemployee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected dividend yield	0.00%	0.00%	0.00%	0.00%
Nonemployee Stock Option [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock price	$ 8.21	$ 12.73	$ 8.21	$ 12.73
Expected option term (in years)	4 years 7 months 2 days	5 years 8 months 23 days	4 years 4 months 13 days	3 months
Expected volatility	66.00%	63.00%	66.00%	56.00%
Risk-free interest rate	1.27%	1.75%	1.21%	0.08%
Nonemployee Stock Option [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock price	$ 12.22	$ 15.02	$ 24.43	$ 41.12
Expected option term (in years)	4 years 9 months	5 years 11 months 23 days	5 years 3 months 15 days	6 years 10 months 10 days
Expected volatility	72.00%	65.00%	72.00%	65.00%
Risk-free interest rate	1.47%	1.92%	1.57%	2.29%
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock price	$ 8.21
Expected option term (in years)	6 years 3 months	6 years 3 months
Expected volatility	71.00%	65.00%
Risk-free interest rate	1.54%
Expected dividend yield	0.00%	0.00%	0.00%	0.00%
Employee Stock Option [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock price		$ 13.32	$ 8.21	$ 13.32
Expected option term (in years)			5 years 6 months	5 years 6 months
Expected volatility			67.00%	64.00%
Risk-free interest rate		1.85%	1.51%	1.79%
Employee Stock Option [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock price		$ 14.27	$ 24.03	$ 19.83
Expected option term (in years)			6 years 3 months	6 years 3 months
Expected volatility			71.00%	65.00%
Risk-free interest rate		2.02%	1.81%	2.02%

Redeemable Convertible Prefer33

Redeemable Convertible Preferred Stock - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Feb. 04, 2014
Conversion of Stock [Line Items]
Issuance of common stock	20,593,117		20,593,117		17,786,867
Adjustment to preferred stock warrant liability recorded in other income (expense)				$ (2,559)
Redeemable Convertible Preferred Stock [Member]
Conversion of Stock [Line Items]
Issuance of common stock						10,589,434
Series C Preferred Stock [Member]
Conversion of Stock [Line Items]
Fair value of preferred stock warrants						$ 2,323
Adjustment to preferred stock warrant liability recorded in other income (expense)	$ 0	$ 0	$ 0	$ (1,888)

Redeemable Convertible Prefer34

Redeemable Convertible Preferred Stock - Summary of Estimated Fair Values of Outstanding Warrants Using Black-Scholes Option-Pricing Model (Detail) - Series C Redeemable Convertible Preferred Stock [Member]	Feb. 04, 2014$ / shares
Temporary Equity [Line Items]
Stock price	$ 32.66
Expected option term (in years)	4 years 4 months 21 days
Expected volatility	65.00%
Risk-free interest rate	1.52%
Expected dividend yield	0.00%

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Assets Measured or Disclosed at Fair Value (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Held-to-maturity investments
U.S. treasury securities and government agency bonds	$ 55,119	$ 72,532
Assets held in restriction
Total	100,177	94,337
Money Market Fund [Member]
Cash equivalents
Money market fund	43,942	20,425
Assets held in restriction
Restricted investments, at fair value	1,116
Money Market Fund And Certificate Of Deposit [Member]
Assets held in restriction
Restricted investments, at fair value		1,380
US Treasury Securities [Member]
Held-to-maturity investments
U.S. treasury securities and government agency bonds	55,119
U.S. Government Treasury and Agency Securities [Member]
Held-to-maturity investments
U.S. treasury securities and government agency bonds		72,532
Level 1[Member]
Assets held in restriction
Total	43,942	20,425
Level 1[Member] | Money Market Fund [Member]
Cash equivalents
Money market fund	43,942	20,425
Level 2 [Member]
Assets held in restriction
Total	56,235	73,912
Level 2 [Member] | Money Market Fund [Member]
Assets held in restriction
Restricted investments, at fair value	1,116
Level 2 [Member] | Money Market Fund And Certificate Of Deposit [Member]
Assets held in restriction
Restricted investments, at fair value		1,380
Level 2 [Member] | US Treasury Securities [Member]
Held-to-maturity investments
U.S. treasury securities and government agency bonds	$ 55,119
Level 2 [Member] | U.S. Government Treasury and Agency Securities [Member]
Held-to-maturity investments
U.S. treasury securities and government agency bonds		$ 72,532

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014
Debt Instrument Fair Value Carrying Value [Abstract]
Transfers between Level 1 and Level 2	$ 0		$ 0
Preferred stock conversion date	Feb. 4, 2014
Preferred stock, warrants outstanding	0	0

Fair Value Measurements - Sch37

Fair Value Measurements - Schedule of Roll-Forward of Company's Liabilities Measured at Fair Value on Recurring Basis Using Unobservable Inputs (Level 3) (Detail) $ in Thousands	9 Months Ended
	Sep. 30, 2014USD ($)
Debt Instrument Fair Value Carrying Value [Abstract]
Balance at the beginning of the period	$ 529
Change in fair value of warrant liability	2,559
Transfers to Level 2	(3,088)
Balance at the end of the period	$ 0

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) - USD ($)	Jul. 11, 2014	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Jun. 30, 2015	Dec. 01, 2014
Loss Contingencies [Line Items]
Certificate of deposit							$ 264,000
Research and development expense		$ 12,142,000	$ 7,489,000	$ 32,708,000	$ 19,546,000
Cambridge Massachusetts , 2014 Operating Lease Agreement [Member]
Loss Contingencies [Line Items]
Operating lease future minimum payments	$ 9,498,000
Operating lease future minimum payments term	6 years
Letter of credit								$ 1,116,000
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	$ 0	0
Termination of license agreement description				The Company may terminate the license agreement at any time upon 90 days written notice
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
Payments on commencement of clinical trial						$ 100,000
Research and development expense				$ 0	$ 100,000
Arbutus Biopharma Corporation License Agreement [Member]
Loss Contingencies [Line Items]
Expenses related to license agreement				3,000,000
Aggregate development milestones and royalty				$ 22,000,000

Litigation - Additional Informa

Litigation - Additional Information (Detail) - USD ($)	Sep. 30, 2015	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Outstanding litigation liabilities	$ 0	$ 0