Regulus Therapeutics (RGLS) 10-Q 9 May 14 2014 Q1 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	3 Months Ended
	Mar. 31, 2014	Apr. 25, 2014
Document Information [Line Items]	'	'
Document Type	'10-Q	'
Amendment Flag	'false	'
Document Period End Date	31-Mar-14	'
Document Fiscal Year Focus	'2014	'
Document Fiscal Period Focus	'Q1	'
Trading Symbol	'RGLS	'
Entity Registrant Name	'REGULUS THERAPEUTICS INC.	'
Entity Central Index Key	'0001505512	'
Current Fiscal Year End Date	'--12-31	'
Entity Filer Category	'Accelerated Filer	'
Entity Common Stock, Shares Outstanding	'	43,356,822

Condensed_Balance_Sheets

Condensed Balance Sheets (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Current assets:	'	'
Cash and cash equivalents	$8,476	$17,807
Short-term investments	106,121	96,198
Contract and other receivables	140	79
Prepaid and other current assets	3,492	3,098
Total current assets	118,229	117,182
Property and equipment, net	3,805	3,768
Intangibles, net	1,095	1,128
Other assets	978	987
Total assets	124,107	123,065
Current liabilities:	'	'
Accounts payable	2,691	1,172
Accrued liabilities	3,279	3,013
Accrued compensation	859	1,297
Current portion of deferred revenue	2,739	4,888
Total current liabilities	9,568	10,370
Convertible notes payable, at fair value	13,403	11,279
Deferred revenue, less current portion	7,488	6,500
Other long-term liabilities	1,361	1,459
Total liabilities	31,820	29,608
Stockholders' equity:	'	'
Common stock, $0.001 par value; 200,000,000 shares authorized, 43,346,014 and 41,787,326 shares issued and outstanding at March 31, 2014 (unaudited) and December 31, 2013, respectively	43	42
Additional paid-in capital	184,131	172,518
Accumulated other comprehensive loss	-59	-16
Accumulated deficit	-91,828	-79,087
Total stockholders' equity	92,287	93,457
Total liabilities and stockholders' equity	$124,107	$123,065

Condensed_Balance_Sheets_Paren

Condensed Balance Sheets (Parenthetical) (USD $)	Mar. 31, 2014	Dec. 31, 2013
Common stock, par value	$0.00	$0.00
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	43,346,014	41,787,326
Common stock, shares outstanding	43,346,014	41,787,326

Condensed_Statements_of_Operat

Condensed Statements of Operations and Comprehensive Loss (USD $)	3 Months Ended
In Thousands, except Share data, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Revenues:	'	'
Total revenues	$1,631	$3,238
Operating expenses:	'	'
Research and development	9,604	6,883
General and administrative	2,732	1,905
Total operating expenses	12,336	8,788
Loss from operations	-10,705	-5,550
Other income (expense):	'	'
Interest and other income	100	72
Interest expense	-11	'
Loss from valuation of convertible note payable	-2,124	-1,761
Loss before income taxes	-12,740	-7,239
Income tax expense (benefit)	1	-10
Net loss	-12,741	-7,229
Other comprehensive loss:	'	'
Unrealized (loss) gain on short-term investments, net	-43	15
Comprehensive loss	-12,784	-7,214
Net loss per share, basic and diluted	($0.30)	($0.20)
Shares used to compute basic and diluted net loss per share	42,690,200	35,872,606
Strategic Alliances and Collaborations	'	'
Revenues:	'	'
Total revenues	$1,631	$3,238

Condensed_Statements_of_Cash_F

Condensed Statements of Cash Flows (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Operating activities	'	'
Net loss	($12,741)	($7,229)
Adjustments to reconcile net loss to net cash used in operating activities	'	'
Depreciation and amortization expense	354	289
Loss from valuation of convertible note payable	2,124	1,761
Stock-based compensation	1,400	787
Amortization of premium on investments, net	443	324
Gain on investments	-1	-1
Loss on disposal of long-term assets	18	1
Deferred income taxes	'	-10
Change in operating assets and liabilities:	'	'
Contracts and other receivables	-61	'
Prepaid and other current assets	-385	-225
Accounts payable	1,519	86
Accrued liabilities	-39	822
Accrued compensation	-438	-588
Deferred revenue	-1,161	-3,238
Deferred rent and other liabilities	-61	66
Net cash used in operating activities	-9,029	-7,155
Investing activities	'	'
Purchases of short-term investments	-39,780	-18,074
Maturities and sales of short-term investments	29,372	2,430
Purchases of property and equipment	-75	-77
Acquisition of intangibles	'	-27
Net cash used in investing activities	-10,483	-15,748
Financing activities	'	'
Proceeds from issuance of common stock, net	9,728	85
Principal payments on other long-term obligations	-34	-28
Proceeds from exercise of stock options	487	116
Net cash provided by financing activities	10,181	173
Net decrease in cash and cash equivalents	-9,331	-22,730
Cash and cash equivalents at beginning of period	17,807	40,552
Cash and cash equivalents at end of period	8,476	17,822
Supplemental disclosure of cash flow information	'	'
Interest paid	11	'
Income taxes paid	1	'
Supplemental disclosure of non-cash investing and financing activities	'	'
Amounts accrued for property and equipment	301	294
Allowance for tenant improvements	'	482
Amounts accrued for patent expenditures, net	'	$15

Basis_of_Presentation_and_Summ

Basis of Presentation and Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2014
Basis of Presentation and Summary of Significant Accounting Policies	'
	1. Basis of Presentation and Summary of Significant Accounting Policies
	Basis of Presentation
	The accompanying unaudited condensed financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”) for interim financial information and the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. In management’s opinion, the accompanying financial statements reflect all adjustments, consisting of normal recurring adjustments, considered necessary for a fair presentation of the results for the interim periods presented.
	Interim financial results are not necessarily indicative of results anticipated for the full year. These unaudited condensed financial statements should be read in conjunction with the Company’s audited financial statements and footnotes included in our Annual Report on Form 10-K for the year ended December 31, 2013, from which the balance sheet information herein was derived.
	Use of Estimates
	Our financial statements are prepared in accordance with GAAP. The preparation of our financial statements requires us to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses and the disclosure of contingent assets and liabilities in our financial statements and accompanying notes. Although these estimates are based on our knowledge of current events and actions we may undertake in the future, actual results may ultimately differ from these estimates and assumptions.
	Revenue Recognition
	Our revenues generally consist of upfront payments for licenses or options to obtain licenses in the future, research and development funding and milestone payments under strategic alliance agreements, as well as funding received under government grants. We recognize revenues when all four of the following criteria are met: (1) persuasive evidence that an arrangement exists; (2) delivery of the products and/or services has occurred; (3) the selling price is fixed or determinable; and (4) collectability is reasonably assured.
	Multiple element arrangements, such as our strategic alliance agreements with Sanofi, AstraZeneca AB (“AstraZeneca”) and GlaxoSmithKline plc (“GSK”), are analyzed to determine whether the deliverables within the agreement can be separated or whether they must be accounted for as a single unit of accounting. Deliverables under the agreement will be accounted for as separate units of accounting provided that (i) a delivered item has value to the customer on a stand-alone basis; and (ii) if the agreement includes a general right of return relative to the delivered item, delivery or performance of the undelivered item is considered probable and substantially in the control of the vendor. The allocation of consideration amongst the deliverables under the agreement is derived using a “best estimate of selling price” if vendor specific objective evidence and third-party evidence of fair value is not available. If the delivered element does not have stand-alone value, the arrangement is then accounted for as a single unit of accounting, and we recognize the consideration received under the arrangement as revenue on a straight-line basis over our estimated period of performance, which for us is often the expected term of the research and development plan.
	Milestones
	We apply the milestone method of accounting to recognize revenue from milestone payments when earned, as evidenced by written acknowledgement from the collaborator or other persuasive evidence that the milestone has been achieved and the payment is non-refundable, provided that the milestone event is substantive. A milestone event is defined as an event (i) that can only be achieved based in whole or in part on either our performance or on the occurrence of a specific outcome resulting from our performance; (ii) for which there is substantive uncertainty at the inception of the arrangement that the event will be achieved; and (iii) that would result in additional payments being due to us. Events for which the occurrence is either contingent solely upon the passage of time or the result of a counterparty’s performance are not considered to be milestone events. A milestone event is substantive if all of the following conditions are met: (i) the consideration is commensurate with either our performance to achieve the milestone, or the enhancement of the value to the delivered item(s) as a result of a specific outcome resulting from our performance to achieve the milestone; (ii) the consideration relates solely to past performance; and (iii) the consideration is reasonable relative to all the deliverables and payment terms (including other potential milestone consideration) within the arrangement.
	We assess whether a milestone is substantive at the inception of each arrangement. If a milestone is deemed non-substantive, we will account for that milestone payment in accordance with the multiple element arrangements guidance and recognize revenue consistent with the related units of accounting for the arrangement over the related performance period.
	Deferred Revenue
	Amounts received prior to satisfying the above revenue recognition criteria are recorded as deferred revenue in the accompanying balance sheets. Amounts not expected to be recognized within the next 12 months are classified as non-current deferred revenue.
	Stock-Based Compensation
	We account for stock-based compensation expense related to stock options granted to employees and members of our board of directors by estimating the fair value of each stock option on the date of grant using the Black-Scholes model. We recognize stock-based compensation expense using the accelerated multiple-option approach. Under the accelerated multiple-option approach (also known as the graded-vesting method), we recognize compensation expense over the requisite service period for each separately vesting tranche of the award as though the award was in substance multiple awards, resulting in accelerated expense recognition over the vesting period. For performance-based awards granted to employees (i) the fair value of the award is determined on the grant date, (ii) we assess the probability of the individual milestones under the award being achieved and (iii) the fair value of the shares subject to the milestone is expensed over the implicit service period commencing once management believes the performance criteria is probable of being met.
	We account for stock options granted to non-employees, which primarily consist of members of our scientific advisory board, using the fair value approach. Stock options granted to non-employees are subject to periodic revaluation over their vesting terms.
	Fair Value Option
	Applicable accounting policies permit entities to choose, at specified election dates, to measure specified items at fair value if the decision about the election is: 1) applied instrument by instrument, 2) irrevocable, and 3) applied to an entire instrument.
	In July 2012, we amended and restated the $5.0 million convertible promissory note originally issued in February 2010 to GSK (the “2010 GSK Note”), which resulted in a debt extinguishment for accounting purposes. Concurrently with the debt extinguishment, we elected the fair value option for the 2010 GSK Note. The difference between the carrying value of the 2010 GSK Note and the fair value of the amended and restated 2010 GSK Note was recorded as a loss on extinguishment of debt to non-operating earnings. Thereafter, any change to the fair value of the amended note is recorded as gain (loss) from valuation of convertible note payable to non-operating earnings.
	Clinical Trial and Pre-Clinical Study Accruals
	We make estimates of our accrued expenses as of each balance sheet date in our financial statements based on the facts and circumstances known to us at that time. Our accrued expenses for pre-clinical studies and clinical trials are based on estimates of costs incurred and fees that may be associated with services provided by clinical trial investigational sites and CROs. Payments under certain contracts with such parties depend on factors such as successful enrollment of patients, site initiation and the completion of clinical trial milestones. In accruing service fees, we estimate the time period over which services will be performed and the level of effort to be expended in each period. If possible, we obtain information regarding unbilled services directly from these service providers. However, we may be required to estimate these services based on other information available to us. If we underestimate or overestimate the activity or fees associated with a study or service at a given point in time, adjustments to research and development expenses may be necessary in future periods. Historically, our estimated accrued liabilities have approximated actual expense incurred. Subsequent changes in estimates may result in a material change in our accruals.
	Recent Accounting Pronouncements
	In July 2013, the FASB issued Accounting Standards Update No. 2013-11, Presentation of an Unrecognized Tax Benefit When a Net Operating Loss Carryforward, a Similar Tax Loss, or a Tax Credit Carryforward Exists (“ASU 2013-11”). This update provides explicit guidance on the financial statement presentation of an unrecognized tax benefit when a net operating loss carryforward, a similar tax loss, or a tax credit carryforward exists. This guidance is effective prospectively for fiscal years, and interim periods within those years, beginning after December 15, 2013, with an option for early adoption. We adopted this guidance in 2014 and it did not have a material impact on our financial condition, results of operations or related financial statement disclosures.

Net_Loss_Per_Share

Net Loss Per Share	3 Months Ended
	Mar. 31, 2014
Net Loss Per Share	'
	2. Net Loss Per Share
	Basic net loss per share is calculated by dividing the net loss by the weighted average number of common shares outstanding for the period, without consideration for common stock equivalents. Diluted net loss per share is calculated by dividing the net loss by the weighted-average number of common share equivalents outstanding for the period determined using the treasury-stock method. Dilutive common stock equivalents are comprised of options outstanding under our stock option plan and convertible notes payable. For all periods presented, there is no difference in the number of shares used to calculate basic and diluted shares outstanding due to our net loss position.
	Potentially dilutive securities not included in the calculation of diluted net loss per share because to do so would be anti-dilutive are as follows (in common equivalent shares):
		Three months ended
		March 31,
		2014		2013
	Common stock options		2,350,252		2,106,093
	Convertible note payable		1,425,127		1,377,817
	Total		3,775,379		3,483,910
	For the three months ended March 31, 2014 we had a convertible note payable outstanding with a principal balance of $5.4 million that was convertible into common shares at $4.00 per share, at the option of the note holder.

Investments

Investments	3 Months Ended
	Mar. 31, 2014
Investments	'
	3. Investments
	We invest our excess cash in commercial paper and debt instruments of financial institutions, corporations, U.S. government-sponsored agencies, and the U.S. Treasury. As of March 31, 2014, our short-term investments had a weighted average maturity of less than two years.
	The following tables summarize our short-term investments (dollars in thousands):
		Maturity		Amortized		Unrealized					Estimated
	As of March 31, 2014	(in years)		cost		Gains		Losses			fair value
	Corporate debt securities		2 or less	$	86,225	$	31	$	(58	)	$	86,198
	Certificates of deposit		3 or less		12,430		—		—			12,430
	Commercial paper		1 or less		7,492		1		—			7,493
	Total			$	106,147	$	32	$	(58	)	$	106,121
		Maturity		Amortized		Unrealized					Estimated
	As of December 31, 2013	(in years)		cost		Gains		Losses			fair value
	Corporate debt securities		2 or less	$	71,402	$	39	$	(25	)	$	71,416
	Certificates of deposit		2 or less		11,710		—		—			11,710
	Commercial paper		1 or less		6,069		2		—			6,071
	Debt securities of U.S. government-sponsored agencies		1 or less		7,000		1					7,001
	Total			$	96,181	$	42	$	(25	)	$	96,198

Fair_Value_Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2014
Fair Value Measurements	'
	4. Fair Value Measurements
	We have certain financial assets and liabilities recorded at fair value which have been classified as Level 1, 2 or 3 within the fair value hierarchy as described in the accounting standards for fair value measurements.
	Applicable accounting guidance defines fair value as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants as of the measurement date. Market participants are buyers and sellers in the principal market that are (i) independent, (ii) knowledgeable, (iii) able to transact, and (iv) willing to transact. The guidance provides an established hierarchy for inputs used in measuring fair value that maximizes the use of observable inputs and minimizes the use of unobservable inputs by requiring that the most observable inputs be used when available. Observable inputs are inputs that market participants would use in valuing the asset or liability and are developed based on market data obtained from independent sources. Unobservable inputs are inputs that reflect our assumptions about the factors that market participants would use in valuing the asset or liability. The guidance prioritizes the inputs used in measuring the fair value into the following hierarchy:
		•		Level 1 includes financial instruments for which quoted market prices for identical instruments are available in active markets.
		•		Level 2 includes financial instruments for which there are inputs other than quoted prices included within Level 1 that are observable for the instrument such as quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets with insufficient volume or infrequent transactions (less active markets) or model-driven valuations in which significant inputs are observable or can be derived principally from, or corroborated by, observable market data.
		•		Level 3 includes financial instruments for which fair value is derived from valuation techniques in which one or more significant inputs are unobservable, including management’s own assumptions.
	The following table presents our fair value hierarchy for assets and liabilities measured at fair value on a recurring basis at March 31, 2014 and December 31, 2013 (in thousands):
			Fair value as of March 31, 2014
			Total		Level 1		Level 2		Level 3
	Assets:
	Cash equivalents		$	7,340	$	7,340	$	—	$	—
	Corporate debt securities			86,198		—		86,198		—
	Certificates of deposit			12,430		—		12,430		—
	Commercial paper			7,493		—		7,493		—
			$	113,461	$	7,340	$	106,121	$	—
	Liabilities:
	Convertible notes payable		$	13,403	$	—	$	—	$	13,403
			Fair value as of December 31, 2013
			Total		Level 1		Level 2		Level 3
	Assets:
	Cash equivalents		$	17,170	$	17,170	$	—	$	—
	Corporate debt securities			71,416		—		71,416		—
	Certificates of deposit			11,710		—		11,710		—
	Debt securities of U.S. government-sponsored agencies			7,001		—		7,001		—
	Commercial paper			6,071		—		6,071		—
			$	113,368	$	17,170	$	96,198	$	—
	Liabilities:
	Convertible notes payable		$	11,279	$	—	$	—	$	11,279
	Changes in the estimated fair value of convertible notes payable from December 31, 2013 through March 31, 2014 are as follows (in thousands):
			Fair Value Measurements
			Using Significant
			Unobservable Inputs
			(Level 3)
	Balance at December 31, 2013		$	11,279
	Change in estimated fair value of convertible notes payable			2,124
	Balance at March 31, 2014		$	13,403
	We obtain pricing information from quoted market prices or quotes from brokers/dealers. We generally determine the fair value of our investment securities using standard observable inputs, including reported trades, broker/dealer quotes, bids and/or offers.
	We used an income approach in the form of a convertible bond valuation model to value the convertible notes payable. The convertible bond model considered the debt and option characteristics of the note. The key inputs to the model as of March 31, 2014 and December 31, 2013 were volatility (65% and 66%, respectively), risk-free rate (0.26% and 0.325%, respectively), and credit spread (7.4% and 7.4%, respectively). The volatility inputs were based on historical and implied volatility of peer companies. Peer companies were materially consistent with those used to determine volatility for stock-based compensation. Beginning in 2014, our historical volatility was included with the peer companies for purposes of estimating volatility. The risk-free rate inputs were based on the yield of US Treasury Strips as of each date. The credit spread inputs were based on an analysis of our creditworthiness and market rates for comparable straight debt instruments. We recorded a loss from the change in valuation of convertible notes payable of $2.1 million and $1.8 million on the condensed statements of operations and comprehensive loss for the three months ended March 31, 2014 and 2013, respectively.

Convertible_Notes_Payable

Convertible Notes Payable	3 Months Ended
	Mar. 31, 2014
Convertible Notes Payable	'
	5. Convertible Notes Payable
	In October 2012, in conjunction with our initial public offering the amended and restated 2010 GSK Note provided for a rollover into a new promissory note (the “Post-IPO GSK Note”), and the Post-IPO GSK Note was established in the principal amount of $5.4 million, with a maturity date of October 9, 2015. At GSK’s option, the Post-IPO GSK Note is convertible into shares of our common stock at any time prior to the maturity date with a conversion equal to the quotient of all outstanding principal and interest divided by our initial public offering price of $4.00 per share, subject to complying with certain threshold ownership percentage limitations. At March 31, 2014 and December 31, 2013, the fair value of the Post-IPO Note was $13.4 million and $11.3 million, respectively, and is classified as “Convertible note payable, at fair value” on the condensed balance sheets.

Stockholders_Equity

Stockholders' Equity	3 Months Ended
	Mar. 31, 2014
Stockholders' Equity	'
	6. Stockholders’ Equity
	Shares Reserved for Future Issuance
	The following shares of common stock are reserved for future issuance at March 31, 2014:
		March 31,
		2014
	Common stock options outstanding		5,815,877
	Common stock options available for future grant		1,928,980
	Employee Stock Purchase Plan		858,625
	Convertible note payable		1,425,127
	Total common shares reserved for future issuance		10,028,609
	The following table summarizes our stock option activity under all stock option plans for the three months ended March 31, 2014 (in thousands):
		Number of			Weighted
		options			average
					exercise
					price
	Options outstanding at December 31, 2013		5,598		$	3.69
	Granted		500		$	8.44
	Exercised		(235	)	$	2.07
	Canceled/forfeited/expired		(47	)	$	4.72
	Options outstanding at March 31, 2014		5,816		$	4.15
	Stock-Based Compensation
	The following table summarizes the weighted average assumptions used to estimate the fair value of stock options and performance stock awards granted under our 2012 Equity Incentive Plan and the shares purchasable under the 2012 Employee Stock Purchase Plan:
		Three months ended
		March 31,
		2014			2013
	Stock options
	Risk-free interest rate		1.9	%		1.2	%
	Volatility		74	%		67.3	%
	Dividend yield		0	%		0	%
	Expected term (years)		6.1			6.1
	Performance stock options
	Risk-free interest rate		2.2	%		—
	Volatility		70.1	%		—
	Dividend yield		0	%		—
	Expected term (years)		6.4			—
	Employee stock purchase plan shares
	Risk-free interest rate		0.1	%		0.1	%
	Volatility		65.2	%		59.7	%
	Dividend yield		0	%		0	%
	Expected term (years)		0.5			0.5
	The following table summarizes the allocation of our stock-based compensation expense for all stock awards (in thousands):
		Three months ended
		March 31,
		2014			2013
	Research and development	$	804		$	499
	General and administrative		596			288
	Total	$	1,400		$	787

Strategic_Alliances_and_Collab

Strategic Alliances and Collaborations	3 Months Ended
	Mar. 31, 2014
Strategic Alliances and Collaborations	'
	7. Strategic Alliances and Collaborations
	The following table summarizes our total net revenues from our strategic alliances and collaborations (in thousands):
		Three months ended
		March 31,
		2014		2013
	Sanofi	$	925	$	2,500
	GSK		144		187
	AstraZeneca		465		465
	Biogen Idec		87		86
	Other		10		—
	Total	$	1,631	$	3,238
	Sanofi
	In July 2012, we amended and restated our collaboration and license agreement with Sanofi to expand the potential therapeutic applications of the microRNA alliance targets to be developed under such agreement. We determined that the elements within the strategic alliance agreement with Sanofi should be treated as a single unit of accounting because the delivered elements did not have stand-alone value to Sanofi. The following elements were delivered as part of the strategic alliance with Sanofi: (1) a license for up to four microRNA targets; and (2) a research license under our technology alliance.
	In June 2013, the original research term expired, upon which we and Sanofi entered into an option agreement pursuant to which Sanofi was granted an exclusive right to negotiate the co-development and commercialization of certain of our unencumbered microRNA programs and we were granted the exclusive right to negotiate with Sanofi for co-development and commercialization of certain miR-21 anti-miRs in oncology and Alport Syndrome. In July 2013, we received an upfront payment of $2.5 million, of which $1.25 million is creditable against future amounts payable by Sanofi to us under any future co-development and commercialization agreement we enter pursuant to the option agreement. Revenue associated with the creditable portion of this payment remained deferred as of March 31, 2014, and will remain deferred until its application to a creditable transaction. The non-creditable portion of this payment, $1.25 million, was recognized as revenue over the option period from the effective date of the option agreement in June 2013 through the expiration of the option period in January 2014.
	In conjunction with the option agreement, we agreed to continue specified research on the miR-21 programs during the option period. We re-evaluated our remaining estimated period of performance from the original research term through the term of the option agreement and amortized the remaining deferred revenue of $10.1 million associated with the initial $25.0 million upfront payment from June 2013 through the expiration of the option period in January 2014.
	In February 2014, we and Sanofi entered into a second amended and restated collaboration and license agreement (the “2014 Sanofi Amendment”) to renew our strategic alliance to discover, develop and commercialize microRNA therapeutics to focus on specific orphan disease and oncology targets. Under the terms of our renewed alliance, Sanofi will have opt-in rights to our preclinical fibrosis program targeting miR-21 for the treatment of Alport Syndrome, our preclinical program targeting miR-21 for oncology indications, and our preclinical program targeting miR-221/222 for hepatocellular carcinoma (“HCC”). We are responsible for developing each of these programs to proof-of-concept, at which time Sanofi has an exclusive option on each program. If Sanofi chooses to exercise its option on any of these programs, Sanofi will reimburse us for a significant portion of our preclinical and clinical development costs and will also pay us an option exercise fee for any such program, provided that $1.25 million of the $2.5 million upfront option fee paid to us by Sanofi in connection with the June 2013 option agreement will be creditable against such option exercise fee. In addition, we will be eligible to receive clinical and regulatory milestone payments and potentially commercial milestone payments for these programs. We also continue to be eligible to receive royalties on microRNA therapeutic products commercialized by Sanofi and will have the right to co-promote these products.
	In connection with the 2014 Sanofi Amendment, we entered into a Common Stock Purchase Agreement (the “Purchase Agreement”), pursuant to which we sold 1,303,780 shares of our common stock to Aventis Holdings, Inc. (“Aventis”), an entity affiliated with Sanofi, in a private placement at a price per share of $7.67 for an aggregate purchase price of $10.0 million. Under the terms of the Purchase Agreement, Aventis may not sell, transfer, make any short sale of, or grant any option for the sale of any common stock issued pursuant to the Purchase Agreement for a 12-month period following its effective date. The Purchase Agreement and the 2014 Sanofi Amendment were negotiated concurrently and were therefore evaluated as a single agreement. Based upon restricted stock studies of similar duration and a Black-Scholes valuation to measure the discount for lack of marketability, approximately $0.4 million of the proceeds from the Purchase Agreement was attributed to the 2014 Sanofi Amendment, and represents the value of the program targeting miR-221/222 target for HCC. As this element does not have stand-alone value, we are recognizing the $0.4 million into revenue ratably over the estimated period of performance of the miR-221/222 program. As of March 31, 2014, deferred revenue associated with the Purchase Agreement and the 2014 Sanofi Amendment was $0.4 million, which we are expecting to recognize over the remaining estimated period of performance of approximately six years.
	We have evaluated the remaining contingent event-based payments under our 2014 Sanofi Amendment and determined that event-based payments for which payment is contingent upon the results of Sanofi’s performance will be recognized as revenue over our remaining estimated period of performance, if any, and when collectability is reasonably assured. We are eligible to receive milestone payments of up to $101.8 million for proof-of-concept option exercise fees (net of $1.25 million creditable, as noted above), $15.0 million for clinical milestones and up to $300.0 million for regulatory and commercial milestones. In addition, we are entitled to receive royalties based on a percentage of net sales of any products from the miR-21 and miR-221/222 programs which, in the case of sales in the United States, will be in the middle of the 10 to 20% range, and, in the case of sales outside of the United States, will range from the low end to the middle of the 10 to 20% range, depending upon the volume of sales. If we exercise our option to co-promote a product, we will continue to be eligible to receive royalties on net sales of each product in the United States at the same rate, unless we elect to share a portion of Sanofi’s profits from sales of such product in the United States in lieu of royalties.
	GSK
	In April 2008, we entered into a strategic alliance with GSK to discover, develop and commercialize novel microRNA-targeted therapeutics to treat inflammatory diseases (the “immuno-inflammatory alliance”). In February 2010, we and GSK expanded the strategic alliance to include hepatitis C virus infection (“HCV”) to discover, develop and commercialize microRNA therapeutics targeting miR-122 for the treatment of HCV (the “HCV alliance”). In June 2012, we amended our immuno-inflammatory alliance to extend the target selection period for the fourth collaboration target. We determined that the elements within the immuno-inflammatory alliance should be treated as a single unit of accounting because the delivered elements, the opt-in licenses for microRNA product candidates, did not have stand-alone value to GSK. As a result of the extension of the target selection period, we extended the amortization period for the remaining deferred revenue to approximately eight years, which represented our new estimated period of performance. As of March 31, 2014, deferred revenue associated with the immuno-inflammatory alliance was $3.4 million, which we are expecting to recognize over the remaining estimated period of performance of approximately six years.
	In June 2013, the HCV alliance was amended to state that RG-101, and other formulations thereof, will be developed by us independently of our alliance for the treatment of HCV. This amendment removed any further milestone or royalty obligations owed by GSK to us as it relates to RG-101. Concurrently with the amendment in June 2013, we recorded the remaining $1.1 million in deferred revenue associated with the upfront payment from the HCV alliance, as our estimated period of performance was complete.
	Immuno-Inflammatory Alliance
	Under the terms of the immuno-inflammatory alliance, if all the product candidates are successfully developed and commercialized through pre-agreed sales targets we could receive milestone payments up to $432.5 million, including up to $15.5 million for preclinical milestones, up to $87.0 million for clinical milestones, up to $150.0 million for regulatory milestones and up to $180.0 million for commercialization milestones. We are also entitled to receive tiered royalties as a percentage of annual sales which can increase up to the low end of the 10 to 20% range.
	We have evaluated the remaining contingent event-based payments under our immuno-inflammatory alliance and determined that the preclinical and clinical payments meet the definition of a substantive milestone. Accordingly, revenue for these achievements will be recognized in its entirety in the period when the milestone is achieved and collectability is reasonably assured. Other contingent event-based payments under the strategic alliance agreement for which payment is contingent upon the results of GSK’s performance will not be accounted for using the milestone method. Such payments will be recognized as revenue over the remaining estimated period of performance, if any, and when collectability is reasonably assured. We can earn the following preclinical milestones: $0.5 million upon the selection of a fourth microRNA target and $5.0 million upon the selection of a development candidate for each of the selected three targets. We can also earn the following clinical milestones for each of the selected three targets: $4.0 million for the initiation of a Phase 1 clinical trial; $5.0 million for the initiation of a Phase 2 clinical trial; and $20.0 million if GSK chooses to opt-in to the program following the completion of a proof-of-concept trial.
	HCV Alliance
	Notwithstanding the foregoing, GSK has retained its interest in the miR-122 program in HCV, and miR-122 remains a collaboration target under the alliance. If the HCV program is successful, we could receive contractual milestone payments up to $144.5 million, including up to $5.5 million for preclinical milestones, up to $29.0 million for clinical milestones, up to $50.0 million for regulatory milestones and up to $60.0 million for commercialization milestones. We are also entitled to receive tiered royalties which can increase up to the low end of the 10 to 20% range on sales from any product that GSK successfully commercializes under this alliance.
	We have evaluated the remaining contingent event-based payments under the HCV alliance and determined that the preclinical and clinical payments meet the definition of a substantive milestone. Accordingly, revenue for these achievements will be recognized in its entirety in the period when the milestone is achieved and collectability is reasonably assured. Other contingent event-based payments under the strategic alliance agreement for which payment is contingent upon the results of GSK’s performance will not be accounted for using the milestone method. Such payments will be recognized as revenue over the remaining estimated period of performance, if any, and when collectability is reasonably assured. We can earn a preclinical milestone of $5.5 million upon the selection of a development candidate. We can also earn the following clinical milestones: $4.0 million for initiation of a Phase 1 clinical trial; $5.0 million for the initiation of a Phase 2 clinical trial; and $20.0 million if GSK chooses to opt-in to the program following the completion of a proof-of-concept trial. We have no obligation to perform any research or development activities unless mutually agreed upon by the parties.
	AstraZeneca
	In August 2012, we entered into a collaboration and license agreement with AstraZeneca. Under the terms of the agreement, we have agreed to collaborate with AstraZeneca to identify, research and develop compounds targeting three microRNA alliance targets primarily in the fields of cardiovascular diseases, metabolic diseases and oncology. Pursuant to the agreement, we granted AstraZeneca an exclusive, worldwide license to thereafter develop, manufacture and commercialize lead compounds designated by AstraZeneca in the course of the collaboration activities against the alliance targets for all human therapeutic uses. Under the terms of the agreement we are required to use commercially reasonable efforts to perform all research, development and manufacturing activities described in the research plan, at our cost, until the acceptance of an IND or the end of the research term, which extends until the fourth anniversary of the date of the agreement, and may be extended only by mutual written agreement of us and AstraZeneca. Following the earlier to occur of the acceptance of an IND in a major market or the end of the research term, AstraZeneca will assume all costs, responsibilities and obligations for further development, manufacture and commercialization of alliance product candidates.
	Under the terms of the agreement, we received an upfront payment of $3.0 million in October 2012. We determined the elements within the strategic alliance agreement should be treated as a single unit of accounting because the delivered element, the license, does not have stand-alone value. As a result, we are recognizing revenue related to the upfront payment on a straight-line basis over our estimated period of performance, which is four years based on the expected term of the research and development plan. If all three targets are successfully developed and commercialized through pre-agreed sales targets, we could receive milestone payments up to $498.0 million, including preclinical milestones of up to $5.0 million upon lead compound identification, up to $123.0 million for clinical milestones, and up to $370.0 million for commercialization milestones. In addition, we are entitled to receive royalties based on a percentage of net sales which will range from the mid-single digits to the low end of 10 to 20%, depending upon the product and the volume of sales, which royalties may be reduced in certain, limited circumstances.
	We have evaluated the contingent event-based payments under our strategic alliance agreement with AstraZeneca and determined that the preclinical payments meet the definition of substantive milestones. Accordingly, revenue for these achievements will be recognized in its entirety in the period when the milestone is achieved and collectability is reasonably assured. Other contingent event-based payments under the strategic alliance agreement for which payment is contingent upon the results of AstraZeneca’s performance will not be accounted for using the milestone method. Such payments will be recognized as revenue over the remaining estimated period of performance, if any, and when collectability is reasonably assured.
	Concurrently with the collaboration and license agreement, we entered into a Common Stock Purchase Agreement (“CSPA”) with AstraZeneca, pursuant to which we agreed to sell to AstraZeneca an aggregate of $25.0 million of our common stock in a private placement concurrently with our initial public offering, at a price per share equal to the initial public offering price. In October 2012, in accordance with the CSPA, we sold AstraZeneca 6,250,000 shares of our common stock at a price per share of $4.00. Further, the CSPA stipulated that AstraZeneca could not sell, transfer, make any short sale of, or grant any option for the sale of any common stock for a 365-day period following the effective date of our initial public offering. Accounting guidance for multiple element arrangements contains a presumption that separate contracts negotiated and/or entered into at or near the same time with the same entity were negotiated as a package and should be evaluated as a single agreement. We valued the discount applied to the shares of common stock due to the one-year restriction. Based upon restricted stock studies of similar duration and a Black-Scholes valuation to measure a discount for lack of marketability, $4.3 million was attributed to the collaboration and license agreement. We continue to recognize the $4.3 million into revenue ratably over the estimated period of performance of the collaboration. As of March 31, 2014, deferred revenue associated with the collaboration and license agreement and CSPA was $4.4 million, which we are expecting to recognize over the remaining contractual term and corresponding estimated period of performance of approximately 2.5 years.
	Biogen Idec
	In August 2012, we entered into a collaboration and license agreement with Biogen Idec pursuant to which we and Biogen Idec have agreed to collaborate on microRNA biomarkers for multiple sclerosis (“MS”). Under the terms of the agreement, we granted Biogen Idec an exclusive, royalty free, worldwide license to our interest in the collaboration intellectual property for the purpose of commercializing non-microRNA products for the treatment, diagnosis and prevention of MS and non-MS diseases and disorders. We also granted Biogen Idec an exclusive, royalty-free, worldwide license, with the right to sublicense, to our interest in the collaboration intellectual property (and a non-exclusive license to our background intellectual property) for the purpose of commercializing products for the diagnosis of MS. We also granted Biogen Idec a right of first negotiation on certain commercial transactions relating to microRNA products which utilize intellectual property developed during the collaboration. Pursuant to the terms of the agreement, in August 2012 we received an upfront payment of $0.8 million. We are also eligible to receive research milestone payments up to an aggregate of $1.3 million. We considered the elements within the collaboration and license agreement as a single unit of accounting because the delivered element, the license, does not have stand-alone value. As a result, we are recognizing revenue relating to the upfront payment of $0.8 million on a straight-line basis over our estimated period of performance, which is approximately two years based on the original expected term of the research and development plan.
	Concurrently with the collaboration and license agreement, we entered into a note purchase agreement with Biogen Idec, pursuant to which we issued a convertible promissory note in the principal amount of $5.0 million. The $5.0 million note plus accrued interest converted into 1,256,232 shares of our common stock upon the closing of our initial public offering in October 2012 at a conversion price of $4.00 per share.
	In June 2013, we amended the collaboration and license agreement to provide for revised terms with respect to Phase I of the research plan and related milestone payment provisions. The Biogen Idec amendment does not modify the maximum dollar amount we were originally eligible to receive in connection with Phase I milestones under the Biogen Idec agreement, or our estimated period of performance.
	We have evaluated the contingent event-based payments under our collaboration and license agreement with Biogen Idec and determined that the research payments meet the definition of substantive milestones. Accordingly, revenue for these achievements will be recognized in its entirety in the period when the milestone is achieved and collectability is reasonably assured. In October 2013 and November 2013, we received research milestone payments totaling $0.3 million. In addition, we can earn the following research milestones: $0.5 million for validation of the microRNA biomarker in a second independent sample set; and $0.5 million upon the refinement of the microRNA biomarker signature from a longitudinal study of patient samples on MS therapy. As of March 31, 2014, deferred revenue associated with the collaboration and license agreement was $0.2 million, which we are expecting to recognize over the remaining estimated period of performance of 7 months.

Related_Party_Transactions

Related Party Transactions	3 Months Ended
	Mar. 31, 2014
Related Party Transactions	'
	8. Related Party Transactions
	We have entered into several agreements with related parties in the ordinary course of business to license intellectual property and to procure administrative and research and development support services.
	In August 2013, we entered into an amendment to the Amended and Restated License and Collaboration Agreement with Isis and Alnylam dated January 1, 2009, as amended in June 2010 and October 2011 (as amended, the “Amendment”). Under the terms of the Amendment, the parties agreed to our use of certain Alnylam-controlled intellectual property concerning the use and manufacture of GalNAc conjugates (“GalNAc Process Technology”) on a non-exclusive basis. We will generally not be permitted to sublicense or otherwise transfer the GalNAc Process Technology and other Alnylam licensed intellectual property rights relating to GalNAc conjugate technology without the prior written consent of Alnylam, subject to certain limited exceptions for sublicenses to third party collaboration partners. There were no financial terms related to this Amendment. Pursuant to our Amended and Restated Services Agreement with Alnylam dated January 1, 2009, we purchased GalNAc-related materials from Alnylam in the three months ended March 31, 2013.
	The following table summarizes the amounts included in our operating expenses as a result of costs incurred from services provided under the Services Agreement (in thousands):
		Three months ended
		March 31,
		2014		2013
	Services performed or out-of-pocket expenses paid to Alnylam	$	—	$	355

Basis_of_Presentation_and_Summ1

Basis of Presentation and Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2014
Basis of Presentation	'
	Basis of Presentation
	The accompanying unaudited condensed financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”) for interim financial information and the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. In management’s opinion, the accompanying financial statements reflect all adjustments, consisting of normal recurring adjustments, considered necessary for a fair presentation of the results for the interim periods presented.
	Interim financial results are not necessarily indicative of results anticipated for the full year. These unaudited condensed financial statements should be read in conjunction with the Company’s audited financial statements and footnotes included in our Annual Report on Form 10-K for the year ended December 31, 2013, from which the balance sheet information herein was derived.
Use of Estimates	'
	Use of Estimates
	Our financial statements are prepared in accordance with GAAP. The preparation of our financial statements requires us to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses and the disclosure of contingent assets and liabilities in our financial statements and accompanying notes. Although these estimates are based on our knowledge of current events and actions we may undertake in the future, actual results may ultimately differ from these estimates and assumptions.
Revenue Recognition	'
	Revenue Recognition
	Our revenues generally consist of upfront payments for licenses or options to obtain licenses in the future, research and development funding and milestone payments under strategic alliance agreements, as well as funding received under government grants. We recognize revenues when all four of the following criteria are met: (1) persuasive evidence that an arrangement exists; (2) delivery of the products and/or services has occurred; (3) the selling price is fixed or determinable; and (4) collectability is reasonably assured.
	Multiple element arrangements, such as our strategic alliance agreements with Sanofi, AstraZeneca AB (“AstraZeneca”) and GlaxoSmithKline plc (“GSK”), are analyzed to determine whether the deliverables within the agreement can be separated or whether they must be accounted for as a single unit of accounting. Deliverables under the agreement will be accounted for as separate units of accounting provided that (i) a delivered item has value to the customer on a stand-alone basis; and (ii) if the agreement includes a general right of return relative to the delivered item, delivery or performance of the undelivered item is considered probable and substantially in the control of the vendor. The allocation of consideration amongst the deliverables under the agreement is derived using a “best estimate of selling price” if vendor specific objective evidence and third-party evidence of fair value is not available. If the delivered element does not have stand-alone value, the arrangement is then accounted for as a single unit of accounting, and we recognize the consideration received under the arrangement as revenue on a straight-line basis over our estimated period of performance, which for us is often the expected term of the research and development plan.
	Milestones
	We apply the milestone method of accounting to recognize revenue from milestone payments when earned, as evidenced by written acknowledgement from the collaborator or other persuasive evidence that the milestone has been achieved and the payment is non-refundable, provided that the milestone event is substantive. A milestone event is defined as an event (i) that can only be achieved based in whole or in part on either our performance or on the occurrence of a specific outcome resulting from our performance; (ii) for which there is substantive uncertainty at the inception of the arrangement that the event will be achieved; and (iii) that would result in additional payments being due to us. Events for which the occurrence is either contingent solely upon the passage of time or the result of a counterparty’s performance are not considered to be milestone events. A milestone event is substantive if all of the following conditions are met: (i) the consideration is commensurate with either our performance to achieve the milestone, or the enhancement of the value to the delivered item(s) as a result of a specific outcome resulting from our performance to achieve the milestone; (ii) the consideration relates solely to past performance; and (iii) the consideration is reasonable relative to all the deliverables and payment terms (including other potential milestone consideration) within the arrangement.
	We assess whether a milestone is substantive at the inception of each arrangement. If a milestone is deemed non-substantive, we will account for that milestone payment in accordance with the multiple element arrangements guidance and recognize revenue consistent with the related units of accounting for the arrangement over the related performance period.
	Deferred Revenue
	Amounts received prior to satisfying the above revenue recognition criteria are recorded as deferred revenue in the accompanying balance sheets. Amounts not expected to be recognized within the next 12 months are classified as non-current deferred revenue.
Stock-Based Compensation	'
	Stock-Based Compensation
	We account for stock-based compensation expense related to stock options granted to employees and members of our board of directors by estimating the fair value of each stock option on the date of grant using the Black-Scholes model. We recognize stock-based compensation expense using the accelerated multiple-option approach. Under the accelerated multiple-option approach (also known as the graded-vesting method), we recognize compensation expense over the requisite service period for each separately vesting tranche of the award as though the award was in substance multiple awards, resulting in accelerated expense recognition over the vesting period. For performance-based awards granted to employees (i) the fair value of the award is determined on the grant date, (ii) we assess the probability of the individual milestones under the award being achieved and (iii) the fair value of the shares subject to the milestone is expensed over the implicit service period commencing once management believes the performance criteria is probable of being met.
	We account for stock options granted to non-employees, which primarily consist of members of our scientific advisory board, using the fair value approach. Stock options granted to non-employees are subject to periodic revaluation over their vesting terms.
Fair Value Option	'
	Fair Value Option
	Applicable accounting policies permit entities to choose, at specified election dates, to measure specified items at fair value if the decision about the election is: 1) applied instrument by instrument, 2) irrevocable, and 3) applied to an entire instrument.
	In July 2012, we amended and restated the $5.0 million convertible promissory note originally issued in February 2010 to GSK (the “2010 GSK Note”), which resulted in a debt extinguishment for accounting purposes. Concurrently with the debt extinguishment, we elected the fair value option for the 2010 GSK Note. The difference between the carrying value of the 2010 GSK Note and the fair value of the amended and restated 2010 GSK Note was recorded as a loss on extinguishment of debt to non-operating earnings. Thereafter, any change to the fair value of the amended note is recorded as gain (loss) from valuation of convertible note payable to non-operating earnings.
Clinical Trial and Pre-Clinical Study Accruals	'
	Clinical Trial and Pre-Clinical Study Accruals
	We make estimates of our accrued expenses as of each balance sheet date in our financial statements based on the facts and circumstances known to us at that time. Our accrued expenses for pre-clinical studies and clinical trials are based on estimates of costs incurred and fees that may be associated with services provided by clinical trial investigational sites and CROs. Payments under certain contracts with such parties depend on factors such as successful enrollment of patients, site initiation and the completion of clinical trial milestones. In accruing service fees, we estimate the time period over which services will be performed and the level of effort to be expended in each period. If possible, we obtain information regarding unbilled services directly from these service providers. However, we may be required to estimate these services based on other information available to us. If we underestimate or overestimate the activity or fees associated with a study or service at a given point in time, adjustments to research and development expenses may be necessary in future periods. Historically, our estimated accrued liabilities have approximated actual expense incurred. Subsequent changes in estimates may result in a material change in our accruals.
Recent Accounting Pronouncements	'
	Recent Accounting Pronouncements
	In July 2013, the FASB issued Accounting Standards Update No. 2013-11, Presentation of an Unrecognized Tax Benefit When a Net Operating Loss Carryforward, a Similar Tax Loss, or a Tax Credit Carryforward Exists (“ASU 2013-11”). This update provides explicit guidance on the financial statement presentation of an unrecognized tax benefit when a net operating loss carryforward, a similar tax loss, or a tax credit carryforward exists. This guidance is effective prospectively for fiscal years, and interim periods within those years, beginning after December 15, 2013, with an option for early adoption. We adopted this guidance in 2014 and it did not have a material impact on our financial condition, results of operations or related financial statement disclosures.

Net_Loss_Per_Share_Tables

Net Loss Per Share (Tables)	3 Months Ended
	Mar. 31, 2014
Potentially Dilutive Securities Not Included in Calculation of Diluted Net Loss per Share	'
	Potentially dilutive securities not included in the calculation of diluted net loss per share because to do so would be anti-dilutive are as follows (in common equivalent shares):
		Three months ended
		March 31,
		2014		2013
	Common stock options		2,350,252		2,106,093
	Convertible note payable		1,425,127		1,377,817
	Total		3,775,379		3,483,910

Investments_Tables

Investments (Tables)	3 Months Ended
	Mar. 31, 2014
Summary of Short-Term Investments	'
	The following tables summarize our short-term investments (dollars in thousands):
		Maturity		Amortized		Unrealized					Estimated
	As of March 31, 2014	(in years)		cost		Gains		Losses			fair value
	Corporate debt securities		2 or less	$	86,225	$	31	$	(58	)	$	86,198
	Certificates of deposit		3 or less		12,430		—		—			12,430
	Commercial paper		1 or less		7,492		1		—			7,493
	Total			$	106,147	$	32	$	(58	)	$	106,121
		Maturity		Amortized		Unrealized					Estimated
	As of December 31, 2013	(in years)		cost		Gains		Losses			fair value
	Corporate debt securities		2 or less	$	71,402	$	39	$	(25	)	$	71,416
	Certificates of deposit		2 or less		11,710		—		—			11,710
	Commercial paper		1 or less		6,069		2		—			6,071
	Debt securities of U.S. government-sponsored agencies		1 or less		7,000		1					7,001
	Total			$	96,181	$	42	$	(25	)	$	96,198

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2014
Fair Value Hierarchy for Assets and Liabilities Measured at Fair Value on Recurring Basis	'
	The following table presents our fair value hierarchy for assets and liabilities measured at fair value on a recurring basis at March 31, 2014 and December 31, 2013 (in thousands):
		Fair value as of March 31, 2014
		Total		Level 1		Level 2		Level 3
	Assets:
	Cash equivalents	$	7,340	$	7,340	$	—	$	—
	Corporate debt securities		86,198		—		86,198		—
	Certificates of deposit		12,430		—		12,430		—
	Commercial paper		7,493		—		7,493		—
		$	113,461	$	7,340	$	106,121	$	—
	Liabilities:
	Convertible notes payable	$	13,403	$	—	$	—	$	13,403
		Fair value as of December 31, 2013
		Total		Level 1		Level 2		Level 3
	Assets:
	Cash equivalents	$	17,170	$	17,170	$	—	$	—
	Corporate debt securities		71,416		—		71,416		—
	Certificates of deposit		11,710		—		11,710		—
	Debt securities of U.S. government-sponsored agencies		7,001		—		7,001		—
	Commercial paper		6,071		—		6,071		—
		$	113,368	$	17,170	$	96,198	$	—
	Liabilities:
	Convertible notes payable	$	11,279	$	—	$	—	$	11,279
Changes in Estimated Fair Value of Convertible Notes Payable	'
	Changes in the estimated fair value of convertible notes payable from December 31, 2013 through March 31, 2014 are as follows (in thousands):
		Fair Value Measurements
		Using Significant
		Unobservable Inputs
		(Level 3)
	Balance at December 31, 2013	$	11,279
	Change in estimated fair value of convertible notes payable		2,124
	Balance at March 31, 2014	$	13,403

Stockholders_Equity_Tables

Stockholders' Equity (Tables)	3 Months Ended
	Mar. 31, 2014
Common Stock Reserved for Future Issuance	'
	The following shares of common stock are reserved for future issuance at March 31, 2014:
		March 31,
		2014
	Common stock options outstanding		5,815,877
	Common stock options available for future grant		1,928,980
	Employee Stock Purchase Plan		858,625
	Convertible note payable		1,425,127
	Total common shares reserved for future issuance		10,028,609
Stock Option Activity	'
	The following table summarizes our stock option activity under all stock option plans for the three months ended March 31, 2014 (in thousands):
		Number of			Weighted
		options			average
					exercise
					price
	Options outstanding at December 31, 2013		5,598		$	3.69
	Granted		500		$	8.44
	Exercised		(235	)	$	2.07
	Canceled/forfeited/expired		(47	)	$	4.72
	Options outstanding at March 31, 2014		5,816		$	4.15
Assumptions Used to Estimate Fair Value of Stock Options and Performance Stock and Employee Stock Purchase Plan	'
	Stock-Based Compensation
	The following table summarizes the weighted average assumptions used to estimate the fair value of stock options and performance stock awards granted under our 2012 Equity Incentive Plan and the shares purchasable under the 2012 Employee Stock Purchase Plan:
		Three months ended
		March 31,
		2014			2013
	Stock options
	Risk-free interest rate		1.9	%		1.2	%
	Volatility		74	%		67.3	%
	Dividend yield		0	%		0	%
	Expected term (years)		6.1			6.1
	Performance stock options
	Risk-free interest rate		2.2	%		—
	Volatility		70.1	%		—
	Dividend yield		0	%		—
	Expected term (years)		6.4			—
	Employee stock purchase plan shares
	Risk-free interest rate		0.1	%		0.1	%
	Volatility		65.2	%		59.7	%
	Dividend yield		0	%		0	%
	Expected term (years)		0.5			0.5
Stock-Based Compensation	'
	The following table summarizes the allocation of our stock-based compensation expense for all stock awards (in thousands):
		Three months ended
		March 31,
		2014			2013
	Research and development	$	804		$	499
	General and administrative		596			288
	Total	$	1,400		$	787

Strategic_Alliances_and_Collab1

Strategic Alliances and Collaborations (Tables)	3 Months Ended
	Mar. 31, 2014
Revenue from Strategic Alliances	'
	The following table summarizes our total net revenues from our strategic alliances and collaborations (in thousands):
		Three months ended
		March 31,
		2014		2013
	Sanofi	$	925	$	2,500
	GSK		144		187
	AstraZeneca		465		465
	Biogen Idec		87		86
	Other		10		—
	Total	$	1,631	$	3,238

Related_Party_Transactions_Tab

Related Party Transactions (Tables)	3 Months Ended
	Mar. 31, 2014
Summary of Operating Expenses from Related Party Activities	'
	The following table summarizes the amounts included in our operating expenses as a result of costs incurred from services provided under the Services Agreement (in thousands):
		Three months ended
		March 31,
		2014		2013
	Services performed or out-of-pocket expenses paid to Alnylam	$	—	$	355

Basis_of_Presentation_and_Summ2

Basis of Presentation and Summary of Significant Accounting Policies - Additional Information (Detail) (Convertible Debt, USD $)	Jul. 31, 2012
In Millions, unless otherwise specified
Convertible Debt	'
Organization And Summary Of Significant Accounting Policies [Line Items]	'
Outstanding principal amount	$5

Potentially_Dilutive_Securitie

Potentially Dilutive Securities Not Included in Calculation of Diluted Net Loss per Share (Detail)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]	'	'
Potentially dilutive securities not included in calculation of diluted net loss per share	3,775,379	3,483,910
Common stock options	'	'
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]	'	'
Potentially dilutive securities not included in calculation of diluted net loss per share	2,350,252	2,106,093
Convertible Notes Payable	'	'
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]	'	'
Potentially dilutive securities not included in calculation of diluted net loss per share	1,425,127	1,377,817

Net_Loss_Per_Share_Additional_

Net Loss Per Share - Additional Information (Detail) (USD $)	Mar. 31, 2014
In Millions, except Per Share data, unless otherwise specified
Schedule Of Earnings Per Share Basic And Diluted [Line Items]	'
Convertible notes payable outstanding	$5.40
Conversion price per share of convertible notes payable	$4

Summary_of_ShortTerm_Investmen

Summary of Short-Term Investments (Detail) (USD $)	3 Months Ended	12 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Investment [Line Items]	'	'
Amortized cost	$106,147	$96,181
Unrealized Gains	32	42
Unrealized Losses	-58	-25
Estimated fair value	106,121	96,198
Corporate Debt Securities	'	'
Investment [Line Items]	'	'
Maturity	'2 or less	'2 or less
Amortized cost	86,225	71,402
Unrealized Gains	31	39
Unrealized Losses	-58	-25
Estimated fair value	86,198	71,416
Certificates of Deposit	'	'
Investment [Line Items]	'	'
Maturity	'3 or less	'2 or less
Amortized cost	12,430	11,710
Estimated fair value	12,430	11,710
Commercial Paper	'	'
Investment [Line Items]	'	'
Maturity	'1 or less	'1 or less
Amortized cost	7,492	6,069
Unrealized Gains	1	2
Estimated fair value	7,493	6,071
Debt securities of U.S. government-sponsored agencies	'	'
Investment [Line Items]	'	'
Maturity	'	'1 or less
Amortized cost	'	7,000
Unrealized Gains	'	1
Estimated fair value	'	$7,001

Fair_Value_Hierarchy_for_Asset

Fair Value Hierarchy for Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $)	Mar. 31, 2014	Mar. 31, 2013
In Thousands, unless otherwise specified
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Assets measured at fair value on a recurring basis	$113,461	$113,368
Convertible Notes Payable	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Liabilities measured at fair value on a recurring basis	13,403	11,279
Cash Equivalents	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Assets measured at fair value on a recurring basis	7,340	17,170
Corporate Debt Securities	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Assets measured at fair value on a recurring basis	86,198	71,416
Certificates of Deposit	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Assets measured at fair value on a recurring basis	12,430	11,710
Debt securities of U.S. government-sponsored agencies	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Assets measured at fair value on a recurring basis	'	7,001
Commercial Paper	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Assets measured at fair value on a recurring basis	7,493	6,071
Fair Value, Inputs, Level 1	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Assets measured at fair value on a recurring basis	7,340	17,170
Fair Value, Inputs, Level 1 | Cash Equivalents	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Assets measured at fair value on a recurring basis	7,340	17,170
Fair Value, Inputs, Level 2	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Assets measured at fair value on a recurring basis	106,121	96,198
Fair Value, Inputs, Level 2 | Corporate Debt Securities	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Assets measured at fair value on a recurring basis	86,198	71,416
Fair Value, Inputs, Level 2 | Certificates of Deposit	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Assets measured at fair value on a recurring basis	12,430	11,710
Fair Value, Inputs, Level 2 | Debt securities of U.S. government-sponsored agencies	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Assets measured at fair value on a recurring basis	'	7,001
Fair Value, Inputs, Level 2 | Commercial Paper	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Assets measured at fair value on a recurring basis	7,493	6,071
Fair Value, Inputs, Level 3 | Convertible Notes Payable	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Liabilities measured at fair value on a recurring basis	$13,403	$11,279

Changes_in_Estimated_Fair_Valu

Changes in Estimated Fair Value of Convertible Notes Payable (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'	'
Change in estimated fair value of convertible notes payable	($2,124)	($1,761)
Fair Value, Inputs, Level 3	'	'
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'	'
Balance at December 31, 2013	11,279	'
Change in estimated fair value of convertible notes payable	2,124	'
Balance at March 31, 2014	$13,403	'

Fair_Value_Measurements_Additi

Fair Value Measurements - Additional Information (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]	'	'
Fair value assumption, volatility rate	65.00%	66.00%
Fair value assumption, risk free rate	0.26%	0.33%
Fair value assumption, credit spread	7.40%	7.40%
Loss from valuation of convertible notes payable	($2,124)	($1,761)

Convertible_Notes_Payable_Addi

Convertible Notes Payable - Additional Information (Detail) (USD $)	1 Months Ended
	Oct. 31, 2012	Mar. 31, 2014	Dec. 31, 2013
Debt Instrument [Line Items]	'	'	'
Conversion date	9-Oct-15	'	'
Conversion price per shares	'	$4	'
Convertible note payable, at fair value	'	$13,403,000	$11,279,000
Convertible Debt | GSK	'	'	'
Debt Instrument [Line Items]	'	'	'
Convertible notes issued	5,400,000	'	'

Common_Stock_Reserved_for_Futu

Common Stock Reserved for Future Issuance (Detail)	Mar. 31, 2014	Dec. 31, 2013
Equity [Line Items]	'	'
Common stock options outstanding	5,816,000	5,598,000
Total common shares reserved for future issuance	10,028,609	'
Common Stock	'	'
Equity [Line Items]	'	'
Common stock options outstanding	5,815,877	'
Common stock shares available for future grant	1,928,980	'
Employee Stock Purchase Plan	'	'
Equity [Line Items]	'	'
Common stock shares available for future grant	858,625	'
Convertible Notes Payable	'	'
Equity [Line Items]	'	'
Total common shares reserved for future issuance	1,425,127	'

Stock_Option_Activity_Detail

Stock Option Activity (Detail) (USD $)	3 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Mar. 31, 2014
Number of options	'
Options outstanding at December 31, 2013	5,598
Granted	500
Exercised	-235
Canceled/forfeited/expired	-47
Options outstanding at March 31, 2014	5,816
Weighted average exercise price	'
Options outstanding at December 31, 2013	$3.69
Granted	$8.44
Exercised	$2.07
Canceled/forfeited/expired	$4.72
Options outstanding at March 31, 2014	$4.15

Assumptions_Used_to_Estimate_F

Assumptions Used to Estimate Fair Value of Stock Options and Performance Stock and Employee Stock Purchase Plan (Detail)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Common stock options	'	'
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]	'	'
Risk-free interest rate	1.90%	1.20%
Volatility	74.00%	67.30%
Dividend yield	0.00%	0.00%
Expected term (years)	'6 years 1 month 6 days	'6 years 1 month 6 days
Performance stock options	'	'
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]	'	'
Risk-free interest rate	2.20%	'
Volatility	70.10%	'
Dividend yield	0.00%	'
Expected term (years)	'6 years 4 months 24 days	'0 years
Employee stock purchase plan shares	'	'
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]	'	'
Risk-free interest rate	0.10%	0.10%
Volatility	65.20%	59.70%
Dividend yield	0.00%	0.00%
Expected term (years)	'6 months	'6 months

StockBased_Compensation_Detail

Stock-Based Compensation (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]	'	'
Stock-based compensation expenses	$1,400	$787
Research and development	'	'
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]	'	'
Stock-based compensation expenses	804	499
General and administrative	'	'
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]	'	'
Stock-based compensation expenses	$596	$288

Revenue_from_Strategic_Allianc

Revenue from Strategic Alliances (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Revenue from External Customer [Line Items]	'	'
Total revenues	$1,631	$3,238
Strategic Alliances and Collaborations	'	'
Revenue from External Customer [Line Items]	'	'
Total revenues	1,631	3,238
Strategic Alliances and Collaborations | Sanofi	'	'
Revenue from External Customer [Line Items]	'	'
Total revenues	925	2,500
Strategic Alliances and Collaborations | GSK	'	'
Revenue from External Customer [Line Items]	'	'
Total revenues	144	187
Strategic Alliances and Collaborations | Astra Zeneca	'	'
Revenue from External Customer [Line Items]	'	'
Total revenues	465	465
Strategic Alliances and Collaborations | Biogen Idec	'	'
Revenue from External Customer [Line Items]	'	'
Total revenues	87	86
Strategic Alliances and Collaborations | Other	'	'
Revenue from External Customer [Line Items]	'	'
Total revenues	$10	'

Strategic_Alliances_and_Collab2

Strategic Alliances and Collaborations - Additional Information (Detail) (USD $)

3 Months Ended

3 Months Ended

1 Months Ended

3 Months Ended

1 Months Ended

1 Months Ended

3 Months Ended

3 Months Ended

3 Months Ended

1 Months Ended

3 Months Ended

3 Months Ended

Mar. 31, 2014

Dec. 31, 2013

Mar. 31, 2014

Feb. 28, 2014

Feb. 28, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Feb. 28, 2014

Jul. 31, 2013

Jul. 31, 2013

Mar. 31, 2014

Jun. 30, 2013

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Oct. 31, 2012

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Nov. 30, 2013

Nov. 30, 2013

Nov. 30, 2013

Mar. 31, 2014

Sanofi

Sanofi

Sanofi

Sanofi

Sanofi

Sanofi

Sanofi

Sanofi

Sanofi

Sanofi

Sanofi

Sanofi

Sanofi

Sanofi

Sanofi

GSK

GSK

GSK

GSK

GSK

GSK

GSK

GSK

GSK

GSK

GSK

GSK

GSK

GSK

GSK

GSK

GSK

GSK

GSK

GSK

GSK

GSK

GSK

GSK

GSK

Astra Zeneca

Astra Zeneca

Astra Zeneca

Astra Zeneca

Astra Zeneca

Astra Zeneca

Astra Zeneca

Astra Zeneca

Biogen Idec

Biogen Idec

Biogen Idec

Biogen Idec

Biogen Idec

Private Placement

Minimum

Minimum

Maximum

Maximum

Clinical

Regulatory and Commercialization Milestones

Proof-of-Concept Trial

Common Stock Purchase Agreement

Development Commercialization And License Agreement

Development Commercialization And License Agreement

Research and Development

Research and Development

Development Commercialization And License Agreement

Immuno-Inflammatory Alliance

Immuno-Inflammatory Alliance

Immuno-Inflammatory Alliance

Immuno-Inflammatory Alliance

Immuno-Inflammatory Alliance

Immuno-Inflammatory Alliance

Immuno-Inflammatory Alliance

Immuno-Inflammatory Alliance

Immuno-Inflammatory Alliance

Immuno-Inflammatory Alliance

Immuno-Inflammatory Alliance

Immuno-Inflammatory Alliance

HCV Alliance

HCV Alliance

HCV Alliance

HCV Alliance

HCV Alliance

HCV Alliance

HCV Alliance

HCV Alliance

HCV Alliance

HCV Alliance

Agreement

Minimum

Maximum

Preclinical

Clinical

Commercialization

Common Stock Purchase Agreements Cspa

Amended Collaboration and License Agreement

Validation Of Micro Rna Biomarker

Longitudinal Study Of Patient Samples On Ms Therapy

Research Tax Credit Carryforward

United States

Outside of the United States

United States

Outside of the United States

Minimum

Maximum

Preclinical

Clinical

Regulatory

Fourth Micro RNA Targets

Development Candidate

Phase One Clinical Trial

Phase Two Clinical Trial

Proof-of-Concept Trial

Commercialization

Minimum

Maximum

Preclinical

Clinical

Regulatory

Phase One Clinical Trial

Phase Two Clinical Trial

Proof-of-Concept Trial

Commercialization Milestones

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Initial upfront option payment

'

'

'

'

'

'

'

'

'

'

'

'

'

$2,500,000

$2,500,000

$25,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$3,000,000

'

'

'

'

'

'

'

$800,000

'

'

'

'

Upfront payment creditable against future accounts receivables

'

'

'

'

'

'

'

'

'

'

'

'

'

1,250,000

1,250,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Upfront payment non-creditable portion recognized

'

'

'

'

'

'

'

'

'

'

'

'

'

'

1,250,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Deferred revenue

'

'

'

400,000

'

'

'

'

'

'

'

'

400,000

'

'

'

10,100,000

'

'

3,400,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

4,300,000

4,400,000

'

'

'

'

'

4,400,000

200,000

'

'

'

'

Sale and issuance of common stock

'

'

'

'

1,303,780

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Price per share

'

'

'

'

$7.67

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Aggregate purchase price

'

'

'

'

10,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Restriction period in which Alliances could not sell, transfer, make any short sale of, or grant any option for the sale of any common stock

'

'

'

'

'12 months

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'365 days

'

'

'

'

'

'

'

'

'

'

'

'

Deferred revenue remaining recognition period

'

'

'6 years

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'6 years

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'2 years 6 months

'

'

'

'

'

'

'7 months

'

'

'

'

Revenue through milestone payments

'

'

'

'

'

'

'

'

'

15,000,000

300,000,000

101,800,000

'

'

'

'

'

'

'

'

432,500,000

'

'

15,500,000

87,000,000

150,000,000

500,000

5,000,000

4,000,000

5,000,000

20,000,000

180,000,000

144,500,000

'

'

5,500,000

29,000,000

50,000,000

4,000,000

5,000,000

20,000,000

60,000,000

'

498,000,000

'

'

5,000,000

123,000,000

370,000,000

'

'

300,000

500,000

500,000

1,300,000

Royalties based on percentage of net sales

'

'

'

'

'

10.00%

10.00%

20.00%

20.00%

'

'

'

'

'

'

'

'

'

'

'

'

10.00%

20.00%

'

'

'

'

'

'

'

'

'

'

10.00%

20.00%

'

'

'

'

'

'

'

'

'

10.00%

20.00%

'

'

'

'

'

'

'

'

'

Deferred revenue recognition period

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'8 years

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Acceleration of remaining amortization of upfront payment

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

1,100,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of collaborative areas granted

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

3

'

'

'

'

'

'

'

'

'

'

'

Collaboration and license agreement date

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'August 2012

'

'

'

'

'

'

'August 2012

'

'

'

'

Expected term of research and development plan

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'4 years

'

'

'

'

'

'

'

'

'

'

'

'

Common stock issue

43,000

42,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

25,000,000

'

'

'

'

'

'

'

'

'

'

'

Common stock issued

43,346,014

41,787,326

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

6,250,000

'

'

'

'

'

'

'

'

'

'

'

'

Price per share

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$4

'

'

'

'

'

'

'

'

'

'

'

'

Restricting common stock valuation measurement period

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'1 year

'

'

'

'

'

'

'

'

'

'

'

'

Revenue recognition period

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'2 years

'

'

'

'

Issued promissory note

$5,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Conversion to common stock

1,256,232

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Conversion rate

$4

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Summary_of_Operating_Expenses_

Summary of Operating Expenses from Related Party Activities (Detail) (Alnylam, USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2013
Alnylam	'
Related Party Transaction [Line Items]	'
Services performed or out-of-pocket expenses paid to Alnylam	$355