Idenix Pharmaceuticals (IDIX) 10-Q 30 Oct 13 2013 Q3 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	9 Months Ended
	Sep. 30, 2013	Oct. 18, 2013
Document Information [Line Items]
Document Type	10-Q
Amendment Flag	FALSE
Document Period End Date	30-Sep-13
Document Fiscal Year Focus	2013
Document Fiscal Period Focus	Q3
Trading Symbol	IDIX
Entity Registrant Name	IDENIX PHARMACEUTICALS INC
Entity Central Index Key	1093649
Current Fiscal Year End Date	-19
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		134,000,750

Condensed_Consolidated_Balance

Condensed Consolidated Balance Sheets (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Current assets:
Cash and cash equivalents	$148,832	$230,826
Restricted cash	1,402	2,103
Receivables from related party	1,657	1,195
Other current assets	4,476	3,668
Total current assets	156,367	237,792
Property and equipment, net	2,920	3,274
Receivables from related party, net of current portion	5,354	6,210
Other assets	3,593	3,589
Total assets	168,234	250,865
Current liabilities:
Accounts payable	3,720	5,771
Accrued expenses	15,892	9,293
Deferred revenue, related party	714	714
Other current liabilities	698	154
Total current liabilities	21,024	15,932
Other long-term liabilities	7,188	7,513
Deferred revenue	4,272	4,272
Deferred revenue, related party, net of current portion	3,452	3,988
Total liabilities	35,936	31,705
Commitments and contingencies (Note 8)
Stockholders' equity:
Common stock, $0.001 par value; 200,000,000 shares authorized at September 30, 2013 and December 31, 2012; 134,000,750 and 133,957,689 shares issued and outstanding at September 30, 2013 and December 31, 2012, respectively	134	134
Additional paid-in capital	933,162	926,671
Accumulated other comprehensive income	744	470
Accumulated deficit	-801,742	-708,115
Total stockholders' equity	132,298	219,160
Total liabilities and stockholders' equity	$168,234	$250,865

Condensed_Consolidated_Balance1

Condensed Consolidated Balance Sheets (Parenthetical) (USD $)	Sep. 30, 2013	Dec. 31, 2012
Common stock, par value	$0.00	$0.00
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	134,000,750	133,957,689
Common stock, shares outstanding	134,000,750	133,957,689

Condensed_Consolidated_Stateme

Condensed Consolidated Statements Of Operations And Comprehensive Income (Loss) (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Revenues:
Collaboration revenue - related party	$19	$32,253	$983	$33,268
Other revenue				36,068
Total revenues	19	32,253	983	69,336
Operating expenses:
Cost of revenues	15	509	715	2,302
Research and development	21,673	13,469	65,460	52,604
General and administrative	8,630	6,164	25,306	16,798
Restructuring charges	3,900		3,900
Intangible asset impairment	0	8,045	0	8,045
Total operating expenses	34,218	28,187	95,381	79,749
Income (loss) from operations	-34,199	4,066	-94,398	-10,413
Other income, net	244	205	772	740
Income (loss) before income taxes	-33,955	4,271	-93,626	-9,673
Income tax expense			-1	-1
Net income (loss)	-33,955	4,271	-93,627	-9,674
Earnings (loss) per common share:
Basic	($0.25)	$0.03
Diluted	($0.25)	$0.03
Basic and diluted net loss per common share	($0.25)		($0.70)	($0.09)
Weighted average number of common shares outstanding:
Basic	133,969	124,770
Diluted	133,969	126,847
Shares used in computing basic and diluted net loss per common share	133,969		133,962	113,671
Comprehensive income (loss):
Net income (loss)	-33,955	4,271	-93,627	-9,674
Changes in other comprehensive income:
Foreign currency translation adjustment	472	163	274	-89
Comprehensive income (loss)	($33,483)	$4,434	($93,353)	($9,763)

Condensed_Consolidated_Stateme1

Condensed Consolidated Statements Of Cash Flows (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Cash flows from operating activities:
Net loss	($93,627)	($9,674)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,434	2,234
Share-based compensation expense	3,857	3,154
Share-based compensation expense related to restructuring	1,662
Revenue adjustment for contingently issuable shares	839	-1,331
Intangible asset impairment		8,045
Other	14	-1
Changes in operating assets and liabilities:
Receivables from related party	-462	-6,679
Other assets	271	-141
Accounts payable	-2,052	-205
Accrued expenses and other current liabilities	6,983	2,749
Deferred revenue		-36,068
Deferred revenue, related party	-536	-21,587
Other liabilities	-335	-998
Net cash used in operating activities	-81,952	-60,502
Cash flows from investing activities:
Purchases of property and equipment	-1,074	-834
Changes in restricted cash	701	-942
Net cash used in investing activities	-373	-1,776
Cash flows from financing activities:
Proceeds from exercise of common stock options	134	5,148
Proceeds from issuance of common stock to related party		291
Proceeds from issuance of common stock, net of offering costs		190,505
Net cash provided by financing activities	134	195,944
Effect of changes in exchange rates on cash and cash equivalents	197	-63
Net increase (decrease) in cash and cash equivalents	-81,994	133,603
Cash and cash equivalents at beginning of period	230,826	118,271
Cash and cash equivalents at end of period	148,832	251,874
Supplemental disclosure of cash flow information:
Change in value of shares of common stock contingently issuable or issued to related party	$839	($520)

Business_Overview

Business Overview	9 Months Ended
	Sep. 30, 2013
Business Overview	1. BUSINESS OVERVIEW
	Overview
	Idenix Pharmaceuticals, Inc., which we refer to together with our wholly owned subsidiaries as Idenix, we, us or our, is a biopharmaceutical company engaged in the discovery and development of drugs for the treatment of human viral diseases with operations in the United States and France. Currently, our primary research and development focus is on the treatment of patients with hepatitis C virus, or HCV, using nucleotide polymerase inhibitors and NS5A inhibitors.
	In October 2013, we received approval to enter clinical trials for IDX21437, our uridine based nucleotide prodrug candidate, in Canada and Belgium and we have initiated enrollment for the healthy volunteer portion of a phase I/II clinical trial. Extensive preclinical testing for IDX21437 demonstrated favorable antiviral activity across genotypes 1-6 and a safety profile which supported advancement into clinical trials.
	In the second quarter of 2013, we submitted an investigational new drug, or IND, application to the U.S. Food and Drug Administration, or FDA, for IDX20963, our uridine based nucleotide prodrug candidate. In June 2013, the FDA requested additional preclinical safety information for IDX20963 which we are currently conducting.
	As part of our ongoing extensive nucleotide discovery effort, we continue to explore and develop a diverse spectrum of nucleotides with novel bases, prodrugs and sugar moieties.
	In January 2013, we entered into a non-exclusive collaboration agreement with Janssen Pharmaceuticals, Inc., or Janssen, for the clinical evaluation of samatasvir (IDX719), our once-daily pan-genotypic NS5A inhibitor, simeprevir (TMC435), a once-daily protease inhibitor jointly developed by Janssen and Medivir AB, or Medivir, and TMC647055, a once-daily non-nucleoside polymerase inhibitor, with low dose ritonavir, being developed by Janssen.
	In May 2013, we initiated a 12-week phase II HELIX-1 clinical trial under the Janssen collaboration evaluating samatasvir, simeprevir and ribavirin in treatment-naïve genotype 1b or 4 HCV-infected patients. Patients in Part A (nc) of the HELIX-1 clinical trial have completed enrollment and we anticipate SVR4 data for these patients to be available in the fourth quarter of 2013. We are planning to initiate a second 12-week phase II clinical trial, HELIX-2, which will evaluate the three direct-acting antiviral, or DAA, combination of samatasvir, simeprevir, and TMC647055 with low-dose ritonavir, with and without ribavirin in genotype 1 HCV-infected patients who are either treatment-naïve or have relapsed after treatment with pegylated interferon and ribavirin.
	Our drug development programs and the potential commercialization of our drug candidates will require substantial cash to fund costs that we incur in connection with preclinical studies and clinical trials, regulatory review, manufacturing and sales and marketing efforts. We have incurred losses in each year since our inception and at September 30, 2013, we had an accumulated deficit of $801.7 million. We expect to incur losses over the next several years as we continue to expand our drug discovery and development efforts. As a result of continuing losses, we may seek additional funding through a combination of public or private financing, collaborative relationships or other arrangements and we may seek a partner who will assist in the future development and commercialization of our drug candidates.
	We are subject to risks common to companies in the biopharmaceutical industry including, but not limited to, the successful development of products, clinical trial uncertainty, regulatory approval, fluctuations in operating results and financial risks, potential need for additional funding, protection of proprietary technology and patent risks, compliance with government regulations, dependence on key personnel and collaboration partners, competition, technological and medical risks and management of growth.
	Basis of Presentation
	The condensed consolidated financial statements reflect the operations of Idenix Pharmaceuticals, Inc. and our wholly owned subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation.
	The accompanying condensed consolidated financial statements are unaudited and have been prepared by us in accordance with generally accepted accounting principles in the United States of America, or GAAP, for interim reporting. Accordingly, these interim financial statements do not include all the information and footnotes required by GAAP for complete financial statements and should be read in conjunction with the audited consolidated financial statements for the year ended December 31, 2012, which are included in our Annual Report on Form 10-K filed with the Securities and Exchange Commission, or SEC, on February 25, 2013. These interim financial statements are unaudited, but in the opinion of management, reflect all adjustments (including normal recurring accruals) necessary for a fair statement of the financial position and results of operations for the interim periods presented. The year ended condensed consolidated balance sheet data presented for comparative purposes was derived from audited financial statements, but does not include all disclosures required by GAAP.
	The preparation of condensed consolidated financial statements in accordance with GAAP requires management to make estimates and judgments that may affect the reported amounts of assets, liabilities, revenues and expenses, and related disclosures of contingent assets and liabilities. On an on-going basis, we evaluate our estimates, judgments and methodologies, including those related to revenue recognition, accrued expenses, clinical trial expenses, impairment and amortization of long-lived assets, share-based compensation, income taxes including the valuation allowance for deferred tax assets, contingencies and litigation. We base our estimates on historical experience and on various other assumptions that are believed to be reasonable, the results of which form the basis for making judgments about the carrying values of assets and liabilities. Actual results may differ from these estimates under different assumptions or conditions.
	The results of operations for the interim periods are not necessarily indicative of the results of operations to be expected for any future period or the fiscal year ending December 31, 2013.
	Recent Accounting Pronouncements
	In February 2013, the Financial Accounting Standards Board, or FASB, issued ASU 2013-02, Reporting of Amounts Reclassified Out of Accumulated Other Comprehensive Income, or ASU No. 2013-02, as an update to Comprehensive Income (Topic 220). The objective of this update is to improve the reporting of reclassifications out of accumulated other comprehensive income. The amendments in this update require an entity to report the effect of significant reclassifications out of accumulated other comprehensive income on the respective line items in net income if the amount being reclassified is required under GAAP to be reclassified in its entirety to net income. For other amounts that are not required under GAAP to be reclassified in their entirety to net income in the same reporting period, an entity is required to cross-reference other disclosures required under GAAP that provide additional detail about those amounts. The amendments do not change the current requirements for reporting net income or other comprehensive income in financial statements. ASU No. 2013-02 became effective on February 1, 2013 and did not have a material impact on our financial statements.

Summary_Of_Significant_Account

Summary Of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2013
Summary Of Significant Accounting Policies	2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
	Revenue Recognition
	Revenue is recognized in accordance with SEC Staff Accounting Bulletin No. 101, Revenue Recognition in Financial Statements, as amended by SEC Staff Accounting Bulletin No. 104, Revenue Recognition, and for revenue arrangements entered into after June 30, 2003, in accordance with the revenue recognition guidance of the FASB. For multiple-element revenue arrangements entered into or materially modified after January 1, 2011, we recognize revenue under Accounting Standards Codification Topic 605, Revenue Recognition.
	We record revenue provided that there is persuasive evidence that an arrangement exists, delivery has occurred or services have been rendered, the price is fixed or determinable and collectability is reasonably assured.
	Collaboration Revenue — Related Party
	In May 2003, we entered into a collaboration with Novartis Pharma AG, or Novartis, relating to the worldwide development and commercialization of our drug candidates, which we refer to as the development and commercialization agreement. In May 2003, we also entered into a stockholders’ agreement with Novartis, which we refer to as the stockholders’ agreement. On July 31, 2012, we and Novartis materially modified our collaboration by executing a termination and revised relationship agreement, which we refer to as the termination agreement, and by amending the stockholders’ agreement, which we refer to as the second amended and restated stockholders’ agreement. Subsequent to August 2012, we recognize revenue related to the termination agreement with Novartis under ASC Topic 605.
	We evaluated our modified arrangement with Novartis and determined that the agreements should continue to be treated as a single unit of accounting. Under the termination agreement, we granted Novartis a non-exclusive license to conduct clinical trials evaluating a combination of any of our and Novartis’ HCV drug candidates after the HCV drug candidates have completed dose-ranging studies, subject to meeting certain criteria. The details of the termination agreement are described more fully in Note 7. The non-exclusive license is the only revenue-generating deliverable remaining under the modified arrangement and since neither vendor-specific objective evidence, or VSOE, nor third-party evidence, or TPE, for the non-exclusive license deliverable was available, the selling price for the non-exclusive license was established using the best estimate of selling price, or BESP. We determined that the BESP of Novartis’ non-exclusive license at July 31, 2012 was $5.0 million which is recognized as collaboration revenue from related party on a straight-line basis over the seven-year term of the non-exclusive license. As of September 30, 2013, the remaining balance of $4.2 million was included in deferred revenue from related party in our condensed consolidated balance sheet. In establishing BESP for the non-exclusive license, we used a discounted cash flow model and considered the likelihood of our and Novartis’ drugs being commercialized, the development and commercialization timeline, discount rate, and probable treatment combination and associated peak sales figures which generate royalty amounts.
	Also under the collaboration with Novartis, if we issue any shares of capital stock, other than in certain situations, Novartis has the right to purchase such number of shares required to maintain its percentage ownership of our voting stock for the same consideration per share paid by others acquiring our stock. This stock subscription right allows Novartis to purchase shares of our common stock when stock options are exercised under certain plans. Commencing in August 2012, the fair value of our common stock that would be issuable to Novartis is recorded as an adjustment to the revenue recognized from the collaboration with Novartis and additional paid-in capital. The fair value of this stock subscription right is estimated on a quarterly basis using a trinomial lattice valuation model which includes inputs of our per share common stock price, exercise prices of outstanding options, expected term of our options and exercise rates as well as assumptions regarding expected volatility and exercise multiples. Our stock price as of the end of each fiscal quarter has a significant impact on the fair value calculation. Typically, if the stock price increases quarter over quarter, the fair value of Novartis’ stock subscription right increases and this increase in the fair value is recorded as a reduction to revenue in the quarter with a corresponding increase to additional paid-in capital. This may result in contra-revenue or negative revenue being recognized in any given fiscal period. This stock subscription right is described more fully in Note 7.
	Cash and Cash Equivalents
	We consider all highly liquid investments purchased with a maturity date of 90 days or less at the date of purchase to be cash equivalents.
	In connection with certain of our operating lease commitments, we issued letters of credit collateralized by cash deposits that were classified as restricted cash on the condensed consolidated balance sheets. Restricted cash amounts have been classified as current assets based on the expected release date of the restrictions.
	Concentration of Credit Risk
	Financial instruments that potentially subject us to concentrations of credit risk primarily consist of cash and cash equivalents and receivables from related party. We invest our excess cash and cash equivalents in interest bearing accounts at major United States financial institutions. Management mitigates credit risk by limiting the investment type and maturity to securities that preserve capital, maintain liquidity and have a high credit quality.
	At September 30, 2013 and December 31, 2012, all of our receivables from related party were due from Novartis related to its obligation under the termination agreement to reimburse us for contractual payments due by us to third-parties (Note 8).
	Fair Value Measurements
	Our financial statements include assets and liabilities that are measured at fair value on a recurring basis as of September 30, 2013 and December 31, 2012. Fair values determined by Level 1 inputs utilize observable data such as quoted prices in active markets. Fair values determined by Level 2 inputs utilize data points other than quoted prices in active markets that are observable either directly or indirectly. Fair values determined by Level 3 inputs utilize unobservable data points in which there is little or no market data, which require the reporting entity to develop its own assumptions.
	At September 30, 2013 and December 31, 2012, we had $121.0 million and $184.0 million, respectively, invested in money market funds. Our money market investments have calculated net asset values and are therefore classified as Level 2. There were no Level 3 assets held at fair value at September 30, 2013 or at December 31, 2012. There were no gross unrealized gains or losses for the three and nine months ended September 30, 2013 or 2012.
	Accrued Expenses
	We accrue expenses we have incurred but have not been invoiced. This process involves estimating the level of service performed by third-parties on our behalf and the associated cost incurred for these services as of each balance sheet date in our financial statements. Examples of estimated accrued expenses in which subjective judgments may be required include services provided by contract organizations for preclinical development, clinical trials and manufacturing of clinical materials. Accruals for amounts due to clinical research organizations are among our most significant estimates. In connection with these service fees, our estimates are most affected by our understanding of the status and timing of services provided relative to the actual level of services incurred by the service providers. The date on which certain services commence, the level of services performed on or before a given date and the cost of services is often subject to our judgment. We make these judgments based upon the facts and circumstances known to us. Advance payments for goods and services that will be used in future research and development activities are expensed when the activity has been performed or when the goods have been received rather than when payment is made.
	Share-Based Compensation
	We recognize share-based compensation for employees and directors using a fair value based method that results in expense being recognized in our condensed consolidated financial statements.
	Intangible Asset and Impairment of Long-Lived Assets
	We evaluate the recoverability of our property and equipment and other long-lived assets when circumstances indicate that an event of impairment may have occurred in accordance with FASB guidance. Determination of recoverability is based on an estimate of undiscounted future cash flows resulting from the use of the assets and their eventual disposition. In the event that such cash flows are not expected to be sufficient to recover the carrying amount of the assets, the assets are written-down to their estimated fair values. Long-lived assets and certain identifiable intangible assets to be disposed of are reported at the lower of carrying amount or fair value less cost to sell.
	In July 2008, we entered into a settlement agreement related to our telbivudine (Tyzeka®/Sebivo®) technology for the treatment of hepatitis B virus, or HBV, described more fully in Note 8. Pursuant to the settlement agreement, we paid the University of Alabama at Birmingham Research Foundation, or UABRF, a $4.0 million upfront payment and agreed to make additional payments to UABRF equal to 20% of all royalty payments received by us from Novartis based on worldwide sales of Tyzeka®/Sebivo®, subject to minimum payment obligations aggregating $11.0 million. Prior to the execution of the termination agreement in July 2012, we were amortizing the $15.0 million related to this settlement payment over the life of the settlement agreement. Under the termination agreement with Novartis, we no longer receive royalty or milestone payments from Novartis based upon worldwide product sales of Tyzeka®/Sebivo®. We concluded that the intangible asset was effectively abandoned on the effective date of the termination agreement since there are no future cash flows associated with its use and the intangible asset has no alternate use. As a result, we recorded an impairment charge of $8.0 million during the three and nine months ended September 30, 2012. No impairment charges were recognized for the three and nine months ended September 30, 2013.

Net_Income_Loss_Per_Common_Sha

Net Income (Loss) Per Common Share	9 Months Ended
	Sep. 30, 2013
Net Income (Loss) Per Common Share	3. NET INCOME (LOSS) PER COMMON SHARE
	Basic net income (loss) per common share is computed by dividing the net income (loss) available to common stockholders by the weighted average number of common shares outstanding during the period. Diluted net income (loss) per common share is computed by dividing the net income (loss) available to common stockholders by the weighted average number of common shares and other potential common shares then outstanding. Potential common shares consist of common shares issuable upon the assumed exercise of outstanding stock options (using the treasury stock method) and the issuance of contingently issuable shares subject to Novartis’ stock subscription rights (Note 7) and restricted stock awards.
	Basic and diluted net loss per share for the three and nine months ended September 30, 2013 and the nine months ended September 30, 2012 were as follows:
		Three Months Ended			Nine Months Ended
		September 30,			September 30,
		2013			2013			2012
		(In Thousands, Except per Share Data)
	Basic and diluted net loss per common share:
	Net loss	$	(33,955	)	$	(93,627	)	$	(9,674	)
	Basic and diluted weighted average number of common shares outstanding		133,969			133,962			113,671
	Basic and diluted net loss per common share	$	(0.25	)	$	(0.70	)	$	(0.09	)
	The following potential common shares were excluded from the calculation of diluted net loss per common share for the three and nine months ended September 30, 2013 and the nine months ended September 30, 2012 because their effect was anti-dilutive:
		Three and Nine Months			Nine Months
		Ended			Ended
		September 30,			September 30,
		2013			2012
		(In Thousands)
	Options		7,536			7,666
	Contingently issuable shares to related party		1,396			709
			8,932			8,375
	In addition to the contingently issuable shares to related party listed in the table above, Novartis could be entitled to additional shares under its stock subscription rights which would be anti-dilutive in future periods based on our current stock price.
	Basic and diluted net income per share for the three months ended September 30, 2012 was as follows:
		Three Months Ended September 30, 2012
		Income			Shares			Amount
		(Numerator)			(Denominator)			per Share
		In Thousands, Except per Share Data
	Basic EPS:
	Income (loss) available to common stockholders	$	4,271			124,770		$	0.03
	Effect of Dilutive Securities:
	Options		—			1,676
	Contingently issuable shares to related party		—			401
	Diluted EPS:
	Income (loss) available to common stockholders	$	4,271			126,847		$	0.03
	There were no common shares excluded from the calculation of diluted net income per common share as of the three months ended September 30, 2012.

Accrued_Expenses

Accrued Expenses	9 Months Ended
	Sep. 30, 2013
Accrued Expenses	4. ACCRUED EXPENSES
	Accrued expenses consisted of the following:
		September 30,		December 31,
		2013		2012
		(In Thousands)
	Research and development contract costs	$	5,810	$	2,686
	Payroll and benefits		2,161		2,946
	Professional fees		3,948		1,204
	Short-term portion of accrued settlement payment		1,036		976
	Restructuring costs		2,090		—
	Other		847		1,481
		$	15,892	$	9,293

Restructuring_Charges

Restructuring Charges	9 Months Ended
	Sep. 30, 2013
Restructuring Charges	5. RESTRUCTURING CHARGES
	In September 2013, we implemented a restructuring of our operations at our headquarters in Cambridge, Massachusetts and at our facility in Montpellier, France to reduce our workforce by approximately 20 positions in connection with our strategic initiatives to create a more flexible business structure and outsource certain research and development functions. We recorded $2.3 million in employee severance charges related to this restructuring. Of this amount, $0.2 million was paid during the third quarter ended September 30, 2013 and the remaining balance of $2.1 million continues to be accrued as of September 30, 2013. We also recorded $1.7 million in non-cash share-based compensation expense related to the acceleration of unvested options for certain employees.

ShareBased_Compensation

Share-Based Compensation	9 Months Ended
	Sep. 30, 2013
Share-Based Compensation	6. SHARE-BASED COMPENSATION
	The following table shows share-based compensation expense as included in our condensed consolidated statements of operations and comprehensive income (loss):
		Three Months Ended September 30,						Nine Months Ended September 30,
		2013			2012			2013		2012
		(In Thousands)						(In Thousands)
	Research and development	$	387		$	495		$	1,382	$	1,277
	General and administrative		835			741			2,475		1,877
	Total share-based compensation expense	$	1,222		$	1,236		$	3,857	$	3,154
	As part of the restructuring in September 2013, we recorded $1.7 million of share-based compensation expense related to the acceleration of unvested options for certain employees. The expense was classified as restructuring charges in our condensed consolidated statements of operations and comprehensive income (loss).
	There were no options granted in the three months ended September 30, 2013 or 2012. The table below illustrates the fair value per share and Black-Scholes option pricing model with the following assumptions used for grants issued for the nine months ended September 30, 2013 and 2012:
		Nine Months Ended September 30,
		2013			2012
	Weighted average fair value of options	$	3.04		$	7.54
	Risk-free interest rate		0.88	%		0.87	%
	Expected dividend yield		—			—
	Expected option term (in years)		5.27			5.32
	Expected volatility		80.3	%		79.3	%
	The expected option term and expected volatility were determined by examining the expected option term and expected volatilities of similarly sized biotechnology companies as well as expected term and expected volatility of our own stock.
	The following table summarizes option activity under the equity incentive plans:
		Number of			Weighted
		Shares			Average Exercise
					Price per Share
	Options outstanding at December 31, 2012		7,555,598		$	7.6
	Granted		1,644,800		$	4.66
	Cancelled		(1,620,842	)	$	9.17
	Exercised		(43,061	)	$	3.1
	Options outstanding at September 30, 2013		7,536,495		$	6.65
	Options exercisable at September 30, 2013		5,127,290		$	6.68
	We had an aggregate of $10.3 million of share-based compensation expense as of September 30, 2013 remaining to be amortized over a weighted average expected term of 2.45 years.

Collaborations

Collaborations	9 Months Ended
	Sep. 30, 2013
Collaborations	7. COLLABORATIONS
	Janssen Pharmaceuticals, Inc. Collaboration
	In January 2013, we entered into a non-exclusive collaboration agreement with Janssen for the clinical evaluation of all oral DAA HCV combination therapies. The combination therapies involve samatasvir (IDX719), our once-daily pan-genotypic NS5A inhibitor, simeprevir (TMC435), a once-daily protease inhibitor jointly developed by Janssen and Medivir, and TMC647055, a once-daily non-nucleoside polymerase inhibitor, with low dose ritonavir, being developed by Janssen.
	Under the terms of this collaboration agreement, we will conduct the clinical trials. Clinical development plans include drug-drug interaction studies, followed by phase II studies as agreed between the companies, pending approval from regulatory authorities.
	In May 2013, we initiated a 12-week phase II HELIX-1 clinical trial evaluating samatasvir, simeprevir and ribavirin in treatment-naïve genotype 1b or 4 HCV-infected patients. Patients in Part A (nc) of the HELIX-1 clinical trial have completed enrollment and we anticipate SVR4 data for these patients to be available in the fourth quarter of 2013. We are planning to initiate a second 12-week phase II clinical trial, HELIX-2, which will evaluate the three-DAA combination of samatasvir, simeprevir, and TMC647055 with low-dose ritonavir, with and without ribavirin in genotype 1 HCV-infected patients who are either treatment-naïve or have relapsed after treatment with pegylated interferon and ribavirin.
	The clinical trials will be conducted under an arrangement whereby Janssen provides us with clinical supply of simeprevir and TMC647055 at no cost. Neither party will receive any milestone or royalty payments from the other party under this agreement. Both companies retain all rights to their respective compounds under this agreement. The parties have no obligation to conduct additional clinical trials beyond those described here. Neither party has licensed any commercial rights to the other party.
	This collaboration agreement may be terminated by either party in certain circumstances. Janssen may terminate the collaboration agreement, in its sole discretion, by providing us with 30 days written notice. If Janssen terminates the collaboration agreement in such instance, it shall reimburse us for certain of our costs associated with the collaboration.
	If either us or Janssen materially breaches the collaboration agreement and does not cure such breach within a specified time period, the non-breaching party may terminate the collaboration agreement in its entirety. Either party may also terminate the collaboration agreement, effective immediately, if the other party files for bankruptcy, is dissolved or has a receiver appointed for substantially all of its property. Either party may also terminate the collaboration agreement to protect the safety, health or welfare of subjects in the trials. We may terminate the collaboration agreement prior to the commencement of certain activities if Janssen’s research development and license agreement with Medivir is terminated.
	Novartis Collaboration
	In May 2003, we entered into the development and commercialization agreement with Novartis related to the worldwide development and commercialization of our drug candidates. In May 2003, we also entered into the stockholders’ agreement with Novartis. In July 2012, we and Novartis materially modified our collaboration by executing the termination agreement and the second amended and restated stockholders’ agreement. As of October 18, 2013, Novartis owned approximately 25% of our outstanding common stock.
	Termination Agreement
	Termination of Novartis’ Option to License our Development Stage Drug Candidates
	Pursuant to the termination agreement entered into in July 2012, Novartis’ option right to license our current and future development-stage drug candidates in any therapeutic area was terminated. In exchange, we agreed to pay Novartis a royalty based on worldwide product sales of our HCV drug products, unless such drug products are prescribed in combination with Novartis’ HCV drug products. The royalty percentage will vary based on our commercialized HCV drug product, but range from the high single digits to the low double digit percentages. Royalties are payable until the later to occur of: a) expiration of the last-to-expire of specified patent rights in a country; or b) ten years after the first commercial sale of a product in such country, provided that if royalties are payable on a product after the expiration of the patent rights in a country, each of the respective royalty rates for such product in such country would be reduced by one-half.
	Novartis’ Non-Exclusive License to Conduct Combination Trials
	Pursuant to the termination agreement, we granted Novartis a non-exclusive license to conduct clinical trials evaluating a combination of any of our and Novartis’ HCV drug candidates after the HCV drug candidates have completed dose-ranging studies, subject to meeting certain criteria. Under certain circumstances Novartis may conduct a dose-ranging study with respect to our HCV drug candidates. We have agreed to supply Novartis with our HCV drug candidates for use in such combination trials. We and Novartis have agreed to use commercially reasonable efforts to, in good faith, enter into a supply agreement and other relevant agreements in connection with any such combination trial. Novartis’ ability to initiate combination trials expires on the seven year anniversary of the execution of the termination agreement, or July 2019, although any then existing combination study commenced prior to such expiration date may continue after the expiration date.
	Since neither VSOE nor TPE for the non-exclusive license deliverable was available, the selling price for this non-exclusive license was established using the BESP. We determined the BESP of the non-exclusive license at July 31, 2012 to be $5.0 million which is recognized as revenue on a straight-line basis over the seven-year term of the non-exclusive license. We recognized $0.1 million and $0.5 million of collaboration revenue related to the non-exclusive license during the three and nine months ended September 30, 2013, respectively. These revenue amounts are impacted by Novartis’ stock subscription rights described below. As of September 30, 2013 and December 31, 2012, we had a balance of $4.2 million and $4.7 million, respectively, of deferred revenue from related party in our condensed consolidated balance sheets.
	Treatment of Product Sales of Tyzeka®/Sebivo® for the Treatment of the Hepatitis B Virus
	Under the termination agreement executed in July 2012, we will no longer receive royalty or milestone payments from Novartis based upon worldwide product sales of Tyzeka®/Sebivo®. Novartis is required to reimburse us for contractual payments to third-parties in connection with intellectual property related to Tyzeka®/Sebivo®. We are otherwise responsible for any payments to third-parties in connection with intellectual property necessary to sell Tyzeka®/Sebivo®. Contractual payments to third-parties are described more fully in Note 8.
	Termination or Breach by Either Party
	If either we or Novartis materially breaches the termination agreement and does not cure such breach within 30 days, the non-breaching party may terminate this agreement in its entirety. Either party may also terminate this agreement, effective immediately, if the other party files for bankruptcy, is dissolved, or has a receiver appointed for substantially all of its property. Novartis may also terminate this agreement for convenience. If Novartis terminates this agreement either because of a material breach by us that has not been cured or because we have filed for bankruptcy, Novartis may, at its election, retain the licenses granted to it by us under the termination agreement to conduct clinical trials evaluating a combination of any of our HCV drug candidates and any of Novartis’ HCV drug candidates and we would remain obligated to make royalty payments to Novartis based on sales of our HCV drug products. If we terminate this agreement either because of a material breach by Novartis that has not been cured or because Novartis has filed for bankruptcy, or if Novartis terminates this agreement for convenience, the licenses granted to Novartis to conduct combination trials terminate and we would remain obligated to make royalty payments to Novartis based on sales of our HCV drug products.
	Indemnification
	We have agreed to indemnify Novartis and its affiliates against losses suffered as a result of our development, manufacture and commercialization of our HCV products. We have also agreed to indemnify Novartis and its affiliates against losses suffered as a result of any breach of representations and warranties in the termination agreement, the development and commercialization agreement and a stock purchase agreement entered into in 2003. Under these agreements with Novartis, we made numerous representations and warranties to Novartis regarding our drug candidates for the treatment of HBV and HCV, including representations regarding ownership of related inventions and discoveries. In the event of a breach of any such representation or warranty by us, Novartis has the right to seek indemnification from us and, under certain circumstances, our stockholders who sold shares to Novartis in 2003, which includes some of our current and former directors and officers, for damages suffered by Novartis as a result of such breach. The amounts for which we and our stockholders could be liable to Novartis could be substantial.
	Future Agreements and Possible Competition with Novartis
	Under the termination agreement, following the receipt of certain data related to a combination trial and upon Novartis’ request, we and Novartis are obligated to use, in good faith, commercially reasonable efforts to negotiate a future agreement for the development, manufacture and commercialization of such combination therapy for the treatment of HCV. Neither party is obligated to negotiate for a period longer than 180 days. Also under the termination agreement, Novartis has a non-exclusive license to conduct clinical trials evaluating a combination of any of our HCV drug candidates and any of Novartis’ HCV drug candidates after certain criteria have been met. If Novartis obtains regulatory approval to co-label a Novartis HCV drug product with one or more of our HCV drug products, Novartis could market and sell a combination that may compete with our drug candidates and/or combination products that we market and sell in the future.
	Second Amended and Restated Stockholders’ Agreement
	In May 2003, we entered into the stockholders’ agreement with Novartis and in July 2012, we amended this agreement by executing the second amended and restated stockholders’ agreement which includes the terms as described below.
	Novartis’ Registration Rights
	Under the second amended and restated stockholders’ agreement, Novartis maintains its rights to cause us to register for resale, under the Securities Act of 1933, as amended, shares held by Novartis and/or its affiliates.
	Corporate Governance Rights
	Under the second amended and restated stockholders’ agreement executed in July 2012, we have agreed to use our reasonable best efforts to nominate for election one designee of Novartis for so long as Novartis and its affiliates own at least 15% of our voting stock. Novartis has the rights to appoint a non-voting observer to any committee of our board of directors. Novartis has no other corporate governance rights under the second amended and restated stockholders’ agreement.
	Novartis’ Stock Subscription Rights
	Under the stockholders’ agreement, if we issued any shares of capital stock, other than in certain situations, Novartis had the right to purchase such number of shares required to maintain its percentage ownership of our voting stock for the same consideration per share paid by others acquiring our stock. Under the second amended and restated stockholders’ agreement, Novartis continues to have the right to purchase such number of shares required to maintain its percentage ownership of our voting stock for either the same consideration per share paid by others acquiring our stock or, in specified situations, for a 10% premium to the consideration per share paid by others acquiring our stock.
	This stock subscription right allows Novartis to purchase shares of our common stock when stock options are exercised under certain plans. Commencing in August 2012, the fair value of our common stock that would be issuable to Novartis is recorded as an adjustment to the revenue recognized from the collaboration with Novartis and additional paid-in capital. The fair value of this stock subscription right is estimated on a quarterly basis using a trinomial lattice valuation model which includes inputs of our per share common stock price, exercise prices of outstanding options, expected term of our options and exercise rates as well as assumptions regarding expected volatility and exercise multiples. Our stock price as of the end of each fiscal quarter has a significant impact on the fair value calculation. Typically, if the stock price increases quarter over quarter, the fair value of Novartis’ stock subscription right increases and this increase in the fair value is recorded as a reduction to revenue in the quarter with a corresponding increase to additional paid-in capital. This may result in contra-revenue or negative revenue being recognized in any given fiscal period.
	The impact of Novartis’ stock subscription rights for the three months ended September 30, 2013 was $1.4 million, which increased additional paid-in capital and reduced license fee revenue. The impact of Novartis’ stock subscription rights for the nine months ended September 30, 2013 was $0.8 million, which increased additional paid-in capital and reduced license fee revenue.

Commitments_And_Contingencies

Commitments And Contingencies	9 Months Ended
	Sep. 30, 2013
Commitments And Contingencies	8. COMMITMENTS AND CONTINGENCIES
	Product and Drug Candidates
	In connection with the resolution of matters relating to certain of our HCV drug candidates, in May 2004, we entered into a settlement agreement with the University of Alabama, or UAB, which provides for a milestone payment of $1.0 million to UAB upon receipt of regulatory approval in the United States to market and sell certain HCV products invented or discovered by our former chief executive officer during the period from November 1, 1999 to November 1, 2000. This settlement agreement also provides that we will pay UAB an amount equal to 0.5% of worldwide net sales of such HCV products with a minimum sales-based payment equal to $12.0 million. Currently, there are no such HCV products approved and therefore there was no related liability recorded as of September 30, 2013.
	We have potential payment obligations under the license agreement with the Universita degli Studi di Cagliari, or the University of Cagliari, pursuant to which we have the exclusive worldwide right to make, use and sell certain HCV and human immunodeficiency virus type-1, or HIV, technologies. We are liable for certain payments to the University of Cagliari if we receive license fees or milestone payments with respect to such technology from a collaborator or other third-party.
	Pursuant to the license agreement between us and UAB, we were granted an exclusive license to the rights that the UABRF, an affiliate of UAB, Emory University and Le Centre National de la Recherche Scientifique, or CNRS, have to a 1995 U.S. patent application and progeny thereof and counterpart patent applications in Europe, Canada, Japan and Australia that cover the use of certain synthetic nucleosides for the treatment of HBV. In July 2008, we entered into a settlement agreement with UAB, UABRF and Emory University relating to our telbivudine technology. Pursuant to this settlement agreement, all contractual disputes relating to patents covering the use of certain synthetic nucleosides for the treatment of HBV and all litigation matters relating to patents and patent applications related to the use of ß-L-2’-deoxy-nucleosides for the treatment of HBV assigned to one or more of Idenix, CNRS and the Universite Montpellier II, or the University of Montpellier, and which cover the use of Tyzeka®/Sebivo® have been resolved. UAB also agreed to abandon certain continuation patent applications it filed in July 2005. Under the terms of the settlement agreement, we paid UABRF (on behalf of UAB and Emory University) a $4.0 million upfront payment and agreed to make additional payments to UABRF equal to 20% of all royalty payments received by us from Novartis from worldwide sales of Tyzeka®/Sebivo®, subject to minimum payment obligations aggregating $11.0 million. Our payment obligations under the settlement agreement expire in August 2019. The settlement agreement was effective on June 1, 2008 and included mutual releases of all claims and covenants not to sue among the parties. It also included a release from a third-party scientist who had claimed to have inventorship rights in certain Idenix/CNRS/University of Montpellier patents. Included in the condensed consolidated balance sheets as of September 30, 2013 and December 31, 2012 was a liability of $6.4 million and $7.2 million, respectively, related to this settlement agreement. Under the termination agreement executed in July 2012, we no longer receive royalty or milestone payments from Novartis based upon worldwide product sales of Tyzeka®/Sebivo®. Novartis is required to reimburse us for our contractual payments to UABRF in connection with our intellectual property related to Tyzeka®/Sebivo®. Included in receivables from related party at September 30, 2013 and December 31, 2012 was $6.7 million and $7.2 million, respectively, for the reimbursement from Novartis for these contractual payments to UABRF.
	In May 2003, we and Novartis entered into an amended and restated agreement with CNRS and the University of Montpellier pursuant to which we worked in collaboration with scientists from CNRS and the University of Montpellier to discover and develop technologies relating to antiviral substances, including telbivudine. This cooperative agreement expired in December 2006, but we retain rights to exploit the patents derived from the collaboration. Under the cooperative agreement, we are obligated to make royalty payments for products derived from such patents, including products for HBV, HCV and HIV. Such payments would be due even in the instance where we licensed such patents to a third-party. Under the termination agreement, we will no longer receive royalty or milestone payments from Novartis based upon worldwide product sales of Tyzeka®/Sebivo®. Novartis was required to reimburse us for our contractual payments to CNRS and the University of Montpellier, subject to our assignment to Novartis of our patent rights under the amended and restated agreement with CNRS and the University of Montpellier within 12 months of the execution of the termination agreement, in connection with our intellectual property related to Tyzeka®/Sebivo. These payments were recorded as receivables from related party on our condensed consolidated balance sheets. Prior to the assignment of such patent rights to Novartis, payments from Novartis to reimburse us for our contractual payments to CNRS and the University of Montpellier were recorded as a deferred payment obligation on our condensed consolidated balance sheets and we charged payments we made to CNRS to cost of revenues on our condensed consolidated statements of operations and comprehensive income (loss). As of July 31, 2013, the patent rights have been assigned to Novartis. As a result, in the third quarter of 2013, we recognized $1.3 million of deferred payments as revenue and we will no longer record our contractual payments to CNRS as cost of revenues.
	Legal Contingency
	In February 2012, an interference was declared by the United States Patent and Trademark Office, or the USPTO, concerning a patent application co-owned by us and a patent owned by Gilead Pharmasset LLC, or Gilead. Both the application and patent claim certain nucleoside compounds useful in treating HCV. An interference is an adversarial proceeding declared by the USPTO when a party has a U.S. patent application that covers the same invention as another patent application or issued patent to determine priority of invention in the United States. An interference proceeding is divided into two stages. The first phase determines the application filing dates each party will have benefit of for the interfering subject matter. The party with the benefit of the earliest application filing date is deemed the ‘senior party’ and the party with the later date is deemed the ‘junior party’.
	In March 2013, the USPTO issued a decision where we were determined to have a later application filing date than Gilead. Therefore we were determined to be the ‘junior party’ and Gilead the ‘senior party’ in the interference. The second phase of the interference commenced in the second quarter of 2013 and will determine which party was first to invent. The party who is deemed first to invent prevails in the interference proceeding. While we cannot predict whether we will prevail in the interference, we intend to vigorously defend this action and any others like it brought by any third-party. We do not believe our co-owned application at issue in the interference is relevant to any compounds we currently have under development. An interference is based upon complex specialized U.S. patent law and the interference proceeding is likely to be expensive and time consuming. In the event we do not prevail in the interference, certain or all claims in our application may not be issued. In the event we do not prevail, we do not believe we will be required to make any payments to any third-parties and therefore we have not recorded a liability associated with this potential contingent matter.
	In June 2012, Gilead Sciences, Inc. filed suit against us in Canadian Federal Court seeking to invalidate one of our issued Canadian patents. Our patent, which is the subject of the Canadian litigation, covers similar subject matter to that patent application at issue in the U.S. interference. In September 2012, Gilead Sciences, Ltd. filed suit against us in the Norway District Court of Oslo seeking to invalidate one of our issued Norwegian patents. Our patent at issue in the potential Norwegian litigation covers similar subject matter to that patent application at issue in the U.S. interference. In January 2013, Gilead Sciences Australia Pty Ltd. commenced proceedings in the Federal Court of Australia seeking a declaration that certain claims of one of our issued Australian patents, covering similar subject matter to that patent application at issue in the U.S. interference, are invalid and an order that such claims be revoked. We do not believe the respective patents at issue in these cases are relevant to any compounds we currently have under development. Gilead Sciences, Inc. may make similar claims or bring additional legal proceedings in the U.S. or other jurisdictions where we have granted patents. While we cannot predict whether we will prevail, we intend to vigorously defend these actions and any others like it brought by any third-party. In the event we do not prevail, we do not believe we will be required to make any payments to any third-parties and therefore we have not recorded a liability associated with this potential contingent matter.
	Operating Leases
	In April 2013, our lease of 46,418 square feet of office and laboratory space located at 320 Bent Street in Cambridge, Massachusetts commenced. In February 2014, our lease payments will include an additional 5,596 square feet of office space located on the premise. The term of the lease is seven years and we have an option to extend the term of this lease agreement for an additional five years beyond the original lease term. In connection with this operating lease for office and laboratory space, we have a letter of credit with a commercial bank for $1.4 million which will expire in September 2014. In April 2013, we terminated our lease for laboratory and office space at 60 Hampshire Street in Cambridge, Massachusetts.
	Indemnification
	We have agreed to indemnify Novartis and its affiliates against losses suffered as a result of the development, manufacture and commercialization of our HCV products. We have also agreed to indemnify Novartis and its affiliates against losses suffered as a result of any breach of representations and warranties in the termination agreement, development and commercialization agreement and a stock purchase agreement entered into in 2003. Under these agreements with Novartis, we made numerous representations and warranties to Novartis regarding our HBV and HCV drug candidates, including representations regarding our ownership of the inventions and discoveries. In the event of a breach of any such representation or warranty by us, Novartis has the right to seek indemnification from us and, under certain circumstances, us and our stockholders who sold shares to Novartis in 2003, which includes some of our current and former directors and officers, for damages suffered by Novartis as a result of such breach. The amounts for which we and our stockholders could be liable to Novartis could be substantial. While it is possible that we may be required to make payments pursuant to the indemnification obligations we have under these agreements, we cannot reasonably estimate the amount of such payments or the likelihood that such payments would be required.
	Under the license agreement with ViiV Healthcare Company, or ViiV, and the stock purchase agreement with GlaxoSmithKline, or GSK, we have agreed to indemnify ViiV as sublicensee, GSK and their affiliates against losses suffered as a result of our breach of representations and warranties in these agreements. We made numerous representations and warranties regarding our non-nucleoside reverse transcriptase inhibitor program regarding our ownership of inventions and discoveries. If one or more of these representations or warranties were not true at the time we made them, we would be in breach of these agreements. In the event of a breach, the parties have the right to seek indemnification from us for damages suffered as a result of such breach. The amounts for which we may be liable could be substantial. While it is possible that we may be required to make payments pursuant to the indemnification obligations we have under these agreements, we cannot reasonably estimate the amount of such payments or the likelihood that such payments would be required.
	Under the Janssen collaboration agreement, we agreed to indemnify Janssen against losses suffered as a result of our breach of representations and warranties in the agreement and/or any injury to a subject in a clinical trial under the collaboration agreement caused by the use or manufacture of samatasvir. We made numerous representations and warranties to Janssen. If one or more of these representations or warranties were not true at the time they were made, we would be in breach of the agreement. In the event of a breach by us or in the event of injury to a subject in a clinical trial under the collaboration agreement caused by the use or manufacture of samatasvir, Janssen has the right to seek indemnification from us for damages suffered as a result of such breach or subject injury. The amounts for which we could be liable to Janssen under these circumstances may be substantial. In the instance where a subject in a clinical trial suffers injury or death and it is not determinable which compound caused the injury or death, each party shall be responsible for defending any third-party claims alleged against the party after the application of our clinical trial insurance, to the extent applicable.

Business_Overview_Policies

Business Overview (Policies)	9 Months Ended
	Sep. 30, 2013
Recent Accounting Pronouncements	Recent Accounting Pronouncements
	In February 2013, the Financial Accounting Standards Board, or FASB, issued ASU 2013-02, Reporting of Amounts Reclassified Out of Accumulated Other Comprehensive Income, or ASU No. 2013-02, as an update to Comprehensive Income (Topic 220). The objective of this update is to improve the reporting of reclassifications out of accumulated other comprehensive income. The amendments in this update require an entity to report the effect of significant reclassifications out of accumulated other comprehensive income on the respective line items in net income if the amount being reclassified is required under GAAP to be reclassified in its entirety to net income. For other amounts that are not required under GAAP to be reclassified in their entirety to net income in the same reporting period, an entity is required to cross-reference other disclosures required under GAAP that provide additional detail about those amounts. The amendments do not change the current requirements for reporting net income or other comprehensive income in financial statements. ASU No. 2013-02 became effective on February 1, 2013 and did not have a material impact on our financial statements.
Revenue Recognition	Revenue Recognition
	Revenue is recognized in accordance with SEC Staff Accounting Bulletin No. 101, Revenue Recognition in Financial Statements, as amended by SEC Staff Accounting Bulletin No. 104, Revenue Recognition, and for revenue arrangements entered into after June 30, 2003, in accordance with the revenue recognition guidance of the FASB. For multiple-element revenue arrangements entered into or materially modified after January 1, 2011, we recognize revenue under Accounting Standards Codification Topic 605, Revenue Recognition.
	We record revenue provided that there is persuasive evidence that an arrangement exists, delivery has occurred or services have been rendered, the price is fixed or determinable and collectability is reasonably assured.
	Collaboration Revenue — Related Party
	In May 2003, we entered into a collaboration with Novartis Pharma AG, or Novartis, relating to the worldwide development and commercialization of our drug candidates, which we refer to as the development and commercialization agreement. In May 2003, we also entered into a stockholders’ agreement with Novartis, which we refer to as the stockholders’ agreement. On July 31, 2012, we and Novartis materially modified our collaboration by executing a termination and revised relationship agreement, which we refer to as the termination agreement, and by amending the stockholders’ agreement, which we refer to as the second amended and restated stockholders’ agreement. Subsequent to August 2012, we recognize revenue related to the termination agreement with Novartis under ASC Topic 605.
	We evaluated our modified arrangement with Novartis and determined that the agreements should continue to be treated as a single unit of accounting. Under the termination agreement, we granted Novartis a non-exclusive license to conduct clinical trials evaluating a combination of any of our and Novartis’ HCV drug candidates after the HCV drug candidates have completed dose-ranging studies, subject to meeting certain criteria. The details of the termination agreement are described more fully in Note 7. The non-exclusive license is the only revenue-generating deliverable remaining under the modified arrangement and since neither vendor-specific objective evidence, or VSOE, nor third-party evidence, or TPE, for the non-exclusive license deliverable was available, the selling price for the non-exclusive license was established using the best estimate of selling price, or BESP. We determined that the BESP of Novartis’ non-exclusive license at July 31, 2012 was $5.0 million which is recognized as collaboration revenue from related party on a straight-line basis over the seven-year term of the non-exclusive license. As of September 30, 2013, the remaining balance of $4.2 million was included in deferred revenue from related party in our condensed consolidated balance sheet. In establishing BESP for the non-exclusive license, we used a discounted cash flow model and considered the likelihood of our and Novartis’ drugs being commercialized, the development and commercialization timeline, discount rate, and probable treatment combination and associated peak sales figures which generate royalty amounts.
	Also under the collaboration with Novartis, if we issue any shares of capital stock, other than in certain situations, Novartis has the right to purchase such number of shares required to maintain its percentage ownership of our voting stock for the same consideration per share paid by others acquiring our stock. This stock subscription right allows Novartis to purchase shares of our common stock when stock options are exercised under certain plans. Commencing in August 2012, the fair value of our common stock that would be issuable to Novartis is recorded as an adjustment to the revenue recognized from the collaboration with Novartis and additional paid-in capital. The fair value of this stock subscription right is estimated on a quarterly basis using a trinomial lattice valuation model which includes inputs of our per share common stock price, exercise prices of outstanding options, expected term of our options and exercise rates as well as assumptions regarding expected volatility and exercise multiples. Our stock price as of the end of each fiscal quarter has a significant impact on the fair value calculation. Typically, if the stock price increases quarter over quarter, the fair value of Novartis’ stock subscription right increases and this increase in the fair value is recorded as a reduction to revenue in the quarter with a corresponding increase to additional paid-in capital. This may result in contra-revenue or negative revenue being recognized in any given fiscal period. This stock subscription right is described more fully in Note 7.
Cash and Cash Equivalents	Cash and Cash Equivalents
	We consider all highly liquid investments purchased with a maturity date of 90 days or less at the date of purchase to be cash equivalents.
	In connection with certain of our operating lease commitments, we issued letters of credit collateralized by cash deposits that were classified as restricted cash on the condensed consolidated balance sheets. Restricted cash amounts have been classified as current assets based on the expected release date of the restrictions.
Concentration of Credit Risk	Concentration of Credit Risk
	Financial instruments that potentially subject us to concentrations of credit risk primarily consist of cash and cash equivalents and receivables from related party. We invest our excess cash and cash equivalents in interest bearing accounts at major United States financial institutions. Management mitigates credit risk by limiting the investment type and maturity to securities that preserve capital, maintain liquidity and have a high credit quality.
	At September 30, 2013 and December 31, 2012, all of our receivables from related party were due from Novartis related to its obligation under the termination agreement to reimburse us for contractual payments due by us to third-parties (Note 8).
Fair Value Measurements	Fair Value Measurements
	Our financial statements include assets and liabilities that are measured at fair value on a recurring basis as of September 30, 2013 and December 31, 2012. Fair values determined by Level 1 inputs utilize observable data such as quoted prices in active markets. Fair values determined by Level 2 inputs utilize data points other than quoted prices in active markets that are observable either directly or indirectly. Fair values determined by Level 3 inputs utilize unobservable data points in which there is little or no market data, which require the reporting entity to develop its own assumptions.
	At September 30, 2013 and December 31, 2012, we had $121.0 million and $184.0 million, respectively, invested in money market funds. Our money market investments have calculated net asset values and are therefore classified as Level 2. There were no Level 3 assets held at fair value at September 30, 2013 or at December 31, 2012. There were no gross unrealized gains or losses for the three and nine months ended September 30, 2013 or 2012.
Accrued Expenses	Accrued Expenses
	We accrue expenses we have incurred but have not been invoiced. This process involves estimating the level of service performed by third-parties on our behalf and the associated cost incurred for these services as of each balance sheet date in our financial statements. Examples of estimated accrued expenses in which subjective judgments may be required include services provided by contract organizations for preclinical development, clinical trials and manufacturing of clinical materials. Accruals for amounts due to clinical research organizations are among our most significant estimates. In connection with these service fees, our estimates are most affected by our understanding of the status and timing of services provided relative to the actual level of services incurred by the service providers. The date on which certain services commence, the level of services performed on or before a given date and the cost of services is often subject to our judgment. We make these judgments based upon the facts and circumstances known to us. Advance payments for goods and services that will be used in future research and development activities are expensed when the activity has been performed or when the goods have been received rather than when payment is made.
Share-Based Compensation	Share-Based Compensation
	We recognize share-based compensation for employees and directors using a fair value based method that results in expense being recognized in our condensed consolidated financial statements.
Intangible Asset and Impairment of Long-Lived Assets	Intangible Asset and Impairment of Long-Lived Assets
	We evaluate the recoverability of our property and equipment and other long-lived assets when circumstances indicate that an event of impairment may have occurred in accordance with FASB guidance. Determination of recoverability is based on an estimate of undiscounted future cash flows resulting from the use of the assets and their eventual disposition. In the event that such cash flows are not expected to be sufficient to recover the carrying amount of the assets, the assets are written-down to their estimated fair values. Long-lived assets and certain identifiable intangible assets to be disposed of are reported at the lower of carrying amount or fair value less cost to sell.
	In July 2008, we entered into a settlement agreement related to our telbivudine (Tyzeka®/Sebivo®) technology for the treatment of hepatitis B virus, or HBV, described more fully in Note 8. Pursuant to the settlement agreement, we paid the University of Alabama at Birmingham Research Foundation, or UABRF, a $4.0 million upfront payment and agreed to make additional payments to UABRF equal to 20% of all royalty payments received by us from Novartis based on worldwide sales of Tyzeka®/Sebivo®, subject to minimum payment obligations aggregating $11.0 million. Prior to the execution of the termination agreement in July 2012, we were amortizing the $15.0 million related to this settlement payment over the life of the settlement agreement. Under the termination agreement with Novartis, we no longer receive royalty or milestone payments from Novartis based upon worldwide product sales of Tyzeka®/Sebivo®. We concluded that the intangible asset was effectively abandoned on the effective date of the termination agreement since there are no future cash flows associated with its use and the intangible asset has no alternate use. As a result, we recorded an impairment charge of $8.0 million during the three and nine months ended September 30, 2012. No impairment charges were recognized for the three and nine months ended September 30, 2013.

Net_Income_Loss_Per_Common_Sha1

Net Income (Loss) Per Common Share (Tables)	9 Months Ended
	Sep. 30, 2013
Basic and Diluted Net Loss per Common Share	Basic and diluted net loss per share for the three and nine months ended September 30, 2013 and the nine months ended September 30, 2012 were as follows:
		Three Months Ended			Nine Months Ended
		September 30,			September 30,
		2013			2013			2012
		(In Thousands, Except per Share Data)
	Basic and diluted net loss per common share:
	Net loss	$	(33,955	)	$	(93,627	)	$	(9,674	)
	Basic and diluted weighted average number of common shares outstanding		133,969			133,962			113,671
	Basic and diluted net loss per common share	$	(0.25	)	$	(0.70	)	$	(0.09	)
Common Shares Excluded from Calculation of Diluted Net Loss per Common Share	The following potential common shares were excluded from the calculation of diluted net loss per common share for the three and nine months ended September 30, 2013 and the nine months ended September 30, 2012 because their effect was anti-dilutive:
		Three and Nine Months			Nine Months
		Ended			Ended
		September 30,			September 30,
		2013			2012
		(In Thousands)
	Options		7,536			7,666
	Contingently issuable shares to related party		1,396			709
			8,932			8,375
Computation of Basic and Diluted Net Income per Share	Basic and diluted net income per share for the three months ended September 30, 2012 was as follows:
		Three Months Ended September 30, 2012
		Income			Shares			Amount
		(Numerator)			(Denominator)			per Share
		In Thousands, Except per Share Data
	Basic EPS:
	Income (loss) available to common stockholders	$	4,271			124,770		$	0.03
	Effect of Dilutive Securities:
	Options		—			1,676
	Contingently issuable shares to related party		—			401
	Diluted EPS:
	Income (loss) available to common stockholders	$	4,271			126,847		$	0.03

Accrued_Expenses_Tables

Accrued Expenses (Tables)	9 Months Ended
	Sep. 30, 2013
Component of Accrued Expenses	Accrued expenses consisted of the following:
		September 30,		December 31,
		2013		2012
		(In Thousands)
	Research and development contract costs	$	5,810	$	2,686
	Payroll and benefits		2,161		2,946
	Professional fees		3,948		1,204
	Short-term portion of accrued settlement payment		1,036		976
	Restructuring costs		2,090		—
	Other		847		1,481
		$	15,892	$	9,293

ShareBased_Compensation_Tables

Share-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2013
Share-Based Compensation Expense	The following table shows share-based compensation expense as included in our condensed consolidated statements of operations and comprehensive income (loss):
		Three Months Ended September 30,						Nine Months Ended September 30,
		2013			2012			2013		2012
		(In Thousands)						(In Thousands)
	Research and development	$	387		$	495		$	1,382	$	1,277
	General and administrative		835			741			2,475		1,877
	Total share-based compensation expense	$	1,222		$	1,236		$	3,857	$	3,154
Fair Value per Share and Black-Scholes Option Pricing Model with Assumptions Used for Grants Issued	The table below illustrates the fair value per share and Black-Scholes option pricing model with the following assumptions used for grants issued for the nine months ended September 30, 2013 and 2012:
		Nine Months Ended September 30,
		2013			2012
	Weighted average fair value of options	$	3.04		$	7.54
	Risk-free interest rate		0.88	%		0.87	%
	Expected dividend yield		—			—
	Expected option term (in years)		5.27			5.32
	Expected volatility		80.3	%		79.3	%
Summary of Option Activity under Equity Incentive Plans	The following table summarizes option activity under the equity incentive plans:
		Number of			Weighted
		Shares			Average Exercise
					Price per Share
	Options outstanding at December 31, 2012		7,555,598		$	7.6
	Granted		1,644,800		$	4.66
	Cancelled		(1,620,842	)	$	9.17
	Exercised		(43,061	)	$	3.1
	Options outstanding at September 30, 2013		7,536,495		$	6.65
	Options exercisable at September 30, 2013		5,127,290		$	6.68

Business_Overview_Additional_I

Business Overview - Additional Information (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Nature Of Operations [Line Items]
Accumulated deficit	($801,742)	($708,115)

Recovered_Sheet1

Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended			1 Months Ended			1 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Jul. 31, 2012	Sep. 30, 2013	Dec. 31, 2012	Jul. 31, 2008	Jul. 31, 2008	Jul. 31, 2008
						Novartis non-exclusive license to conduct combination trials	Novartis non-exclusive license to conduct combination trials	Novartis non-exclusive license to conduct combination trials	UABRF	UABRF	UABRF
										Up Front Payment	Additional Payment
Schedule Of Significant Accounting Policies [Line Items]
Deferred revenue, related party						$5,000,000	$4,200,000	$4,700,000
Terms of the termination and revised relationship agreement with a related party						7 years
Maturity period of cash and cash equivalents			90 days
Fair value of cash and cash equivalents	121,000,000		121,000,000		184,000,000
Assets held at fair value	0		0		0
Gross unrealized gains or losses in fair value	0	0	0	0
Intangible asset, net									15,000,000	4,000,000	11,000,000
Percentage of payments to third-party based on royalties received from related party									20.00%
Execution date of termination and revised relationship agreement with related party									2012-07
Asset impairment charges	$0	$8,045,000	$0	$8,045,000

Basic_and_Diluted_Net_Loss_Per

Basic and Diluted Net Loss Per Common Share (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Basic and diluted net loss per common share:
Net loss	($33,955)	$4,271	($93,627)	($9,674)
Basic and diluted weighted average number of common shares outstanding	133,969		133,962	113,671
Basic and diluted net loss per common share	($0.25)		($0.70)	($0.09)

Common_Shares_Excluded_from_Ca

Common Shares Excluded from Calculation of Diluted Net Loss Per Common Share (Detail)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Schedule Of Computation Of Basic And Diluted Earnings Per Common Share [Line Items]
Contingently issuable shares to a related party excluded from calculation of earnings per common share	1,396		1,396	709
Antidilutive securities excluded from computation of earnings per share amount	8,932	0	8,932	8,375
Option
Schedule Of Computation Of Basic And Diluted Earnings Per Common Share [Line Items]
Antidilutive securities excluded from computation of earnings per share amount	7,536		7,536	7,666

Computation_of_Basic_and_Dilut

Computation of Basic and Diluted Net Income Per Share (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Schedule Of Computation Of Basic And Diluted Earnings Per Common Share [Line Items]
Income (loss) available to stockholders	($33,955)	$4,271	($93,627)	($9,674)
Effect of Dilutive Securities: Options, Value
Effect of Dilutive Securities: Contingently issuable shares to related party, Value
Income (loss) available to stockholders	($33,955)	$4,271	($93,627)	($9,674)
Basic EPS: Number of share outstanding	133,969	124,770
Effect of Dilutive Securities: Options, Shares		1,676
Effect of Dilutive Securities: Contingently issuable shares to related party, Shares		401
Diluted EPS: Number of share outstanding	133,969	126,847
Basic EPS:
Basic EPS	($0.25)	$0.03
Diluted EPS:
Diluted EPS	($0.25)	$0.03

Net_Income_Loss_Per_Common_Sha2

Net Income (Loss) Per Common Share - Additional Information (Detail)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Net Income Loss Per Common Share [Line Items]
Antidilutive securities excluded from computation of earnings per share amount	8,932	0	8,932	8,375

Component_of_Accrued_Expenses_

Component of Accrued Expenses (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Schedule of Accrued Liabilities [Line Items]
Research and development contract costs	$5,810	$2,686
Payroll and benefits	2,161	2,946
Professional fees	3,948	1,204
Short-term portion of accrued settlement payment	1,036	976
Restructuring costs	2,090
Other	847	1,481
Total accrued expenses	$15,892	$9,293

Restructuring_Charges_Addition

Restructuring Charges - Additional Information (Detail) (USD $)	9 Months Ended
	Sep. 30, 2013
	Employee
Restructuring Cost and Reserve [Line Items]
Positions eliminated	20
Severance payments for restructuring	$2,300,000
Payments for restructuring	200,000
Restructuring reserve	2,100,000
Share-based compensation expense related to restructuring	$1,662,000

ShareBased_Compensation_Expens

Share-Based Compensation Expense (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$1,222	$1,236	$3,857	$3,154
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	387	495	1,382	1,277
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$835	$741	$2,475	$1,877

ShareBased_Compensation_Additi

Share-Based Compensation - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense related to restructuring			$1,662,000
Option Granted	0	0	1,644,800
Share-based compensation expense remaining to be amortized	$10,300,000		$10,300,000
Weighted average expected term	2 years 5 months 12 days		2 years 5 months 12 days

Fair_Value_Per_Share_and_Black

Fair Value Per Share and Black-Scholes Option Pricing Model with Assumptions used for Grants Issued (Detail) (USD $)	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average fair value of options	$3.04	$7.54
Risk-free interest rate	0.88%	0.87%
Expected dividend yield
Expected option term	5 years 3 months 7 days	5 years 3 months 26 days
Expected volatility	80.30%	79.30%

Summary_of_Option_Activity_und

Summary of Option Activity under Equity Incentive Plans (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013
Number of Shares
Option outstanding, Beginning Balance			7,555,598
Granted	0	0	1,644,800
Cancelled			-1,620,842
Exercised			-43,061
Options outstanding, Ending Balance	7,536,495		7,536,495
Options exercisable, at end of the period	5,127,290		5,127,290
Weighted Average Exercise Price per Share
Options outstanding, Beginning Balance			$7.60
Granted			$4.66
Cancelled			$9.17
Exercised			$3.10
Options outstanding, Ending Balance	$6.65		$6.65
Exercisable at end of the period	$6.68		$6.68

Collaborations_Additional_Info

Collaborations - Additional Information (Detail) (USD $)	3 Months Ended	9 Months Ended	1 Months Ended		1 Months Ended			3 Months Ended	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2013	Jul. 31, 2012	Oct. 18, 2013	Jul. 31, 2012	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013	Sep. 30, 2013
			Novartis	Novartis	Novartis non-exclusive license to conduct combination trials	Novartis non-exclusive license to conduct combination trials	Novartis non-exclusive license to conduct combination trials	Novartis non-exclusive license to conduct combination trials	Novartis non-exclusive license to conduct combination trials
				Subsequent Event				Collaboration revenue related to the non-exclusive license	Collaboration revenue related to the non-exclusive license
Collaboration Agreements [Line Items]
Common stock outstanding, ownership percentage				25.00%
Term, in years, through which royalties are payable to a related party			Ten years after the first commercial sale of a product
Reduced rate of royalty after the expiration of agreed upon term with related party			One-half
Terms of the termination and revised relationship agreement with a related party					7 years
Deferred revenue, related party					$5	$4.20	$4.70
Deferred revenue, related party, recognized								0.1	0.5
Breach of termination agreement, maximum days to cure			30 days
Negotiation obligation period for parties			180 days
Minimum percentage of voting stock owned by related party to nominate for election as director at least one related party designee			15.00%
Percentage premium to the consideration per share paid by others for related party to purchase shares			10.00%
Impact on additional paid-in capital as a result of related party's stock subscription rights	$1.40	$0.80

Commitments_and_Contingencies_

Commitments and Contingencies - Additional Information (Detail) (USD $)

1 Months Ended

3 Months Ended

1 Months Ended

1 Months Ended

Jul. 31, 2012

31-May-04

Sep. 30, 2013

Dec. 31, 2012

Apr. 30, 2013

Sep. 30, 2013

Feb. 28, 2014

Jul. 31, 2008

Jul. 31, 2008

Jul. 31, 2008

Sep. 30, 2013

Dec. 31, 2012

Office and Laboratory Space

Office and Laboratory Space

Scenario, Forecast

UABRF

UABRF

UABRF

Novartis Reimbursement

Novartis Reimbursement

sqft

Office and Laboratory Space

Up Front Payment

Additional Payment

University Of Alabama At Birmingham

University Of Alabama At Birmingham

sqft

Commitments and Contingencies Disclosure [Line Items]

Potential milestone payment related to a settlement agreement with a third-party

$1,000,000

Percentage of payments made towards settlement agreement on net sales

0.50%

Minimum sales-based payment pursuant to settlement agreement

12,000,000

Liability recorded as result of settlement agreement

0

Intangible asset, net

15,000,000

4,000,000

11,000,000

Percentage of payments to third-party based on royalties received from related party

20.00%

Related party transaction, due from (to) related party

6,700,000

7,200,000

Settlement agreement related to intangible asset, expiration date

2019-08

Terms in which the entity must assign patent rights to a related party

12 months

Deferred payments recognized as revenue

1,300,000

Area of lease

46,418

5,596

Term of lease

7 years

Additional option to extend term of this lease agreement

5 years

Restricted cash

$1,402,000

$2,103,000

$1,400,000