Entity Central Index Key Document Document and Entity Information [Abstract] Document Document And Entity Information [Abstract] Document Document And Entity Information [Abstract] Entities [Table] Entities [Table] Legal Entity [Axis] Legal Entity [Axis] Entity [Domain] Entity [Domain] Document Information [Line Items] Document Information [Line Items] Document Type Document Type Amendment Flag Amendment Flag Document Period End Date Document Period End Date Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Trading Symbol Trading Symbol Entity Registrant Name Entity Registrant Name Entity Central Index Key Current Fiscal Year End Date Current Fiscal Year End Date Entity Filer Category Entity Filer Category Entity Common Stock, Shares Outstanding Entity Common Stock Shares Outstanding Statement Of Financial Position [Abstract] Statement Of Financial Position [Abstract] Statement [Table] Statement [Table] Statement [Line Items] Statement [Line Items] Current assets: Assets Current [Abstract] Cash and cash equivalents Cash And Cash Equivalents At Carrying Value Short-term investments Short Term Investments Receivables from collaborations Accounts Receivable Net Current Prepaid expenses and other current assets Prepaid Expense And Other Assets Current Total current assets Assets Current Property and equipment, net Property Plant And Equipment Net Long-term investments Long Term Investments Other assets Other Assets Noncurrent Total assets Assets Current liabilities: Liabilities Current [Abstract] Accounts payable Accounts Payable Current Accrued compensation and employee benefits Employee Related Liabilities Current Accrued and other liabilities Accounts Payable And Other Accrued Liabilities Current Deferred revenue, current portion Deferred Revenue Current Total current liabilities Liabilities Current Deferred revenue, long-term Deferred Revenue Noncurrent Other long-term liabilities Other Liabilities Noncurrent Total liabilities Liabilities Stockholders’ equity: Stockholders Equity [Abstract] Preferred stock, $0.001 par value, 5,000,000 shares authorized at March 31, 2014 and December 31, 2013; 0 shares issued and outstanding at March 31, 2014 and December 31, 2013 Preferred Stock Value Common stock, $0.001 par value, 100,000,000 shares authorized at March 31, 2014 and December 31, 2013; 41,120,789 and 40,915,130 shares issued and outstanding at March 31, 2014 and December 31, 2013, respectively Common Stock Value Additional paid-in capital Additional Paid In Capital Accumulated deficit Retained Earnings Accumulated Deficit Accumulated other comprehensive income Accumulated Other Comprehensive Income Loss Net Of Tax Total stockholders’ equity Stockholders Equity Total liabilities and stockholders’ equity Liabilities And Stockholders Equity Preferred stock, par value Preferred Stock Par Or Stated Value Per Share Preferred stock, shares authorized Preferred Stock Shares Authorized Preferred stock, shares issued Preferred Stock Shares Issued Preferred stock, shares outstanding Preferred Stock Shares Outstanding Common stock, par value Common Stock Par Or Stated Value Per Share Common stock, shares authorized Common Stock Shares Authorized Common stock, shares issued Common Stock Shares Issued Common stock, shares outstanding Common Stock Shares Outstanding Interest and Other Nonoperating Income (Expense), Net Income Statement [Abstract] Income Statement [Abstract] Collaboration and license revenue License And Services Revenue Operating expenses: Operating Expenses [Abstract] Research and development Research And Development Expense General and administrative General And Administrative Expense Total operating expenses Operating Expenses Loss from operations Operating Income Loss Interest and other income (expense), net Interest And Other Nonoperating Income Expense Net Net loss Net Income Loss Net loss per share attributable to common stockholders: Earnings Per Share [Abstract] Basic and diluted Earnings Per Share Basic And Diluted Shares used to compute net loss per share attributable to common stockholders: Weighted Average Number Of Shares Outstanding [Abstract] Basic and diluted Weighted Average Number Of Share Outstanding Basic And Diluted Statement Of Income And Comprehensive Income [Abstract] Statement Of Income And Comprehensive Income [Abstract] Net loss Other comprehensive loss: Other Comprehensive Income Loss Net Of Tax Period Increase Decrease [Abstract] Unrealized loss on available-for-sale securities, net of tax Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Net Of Tax Total comprehensive loss Comprehensive Income Net Of Tax Statement Of Cash Flows [Abstract] Statement Of Cash Flows [Abstract] Operating activities Net Cash Provided By Used In Operating Activities [Abstract] Net loss Adjustments to reconcile net loss to cash used in operating activities: Adjustments To Reconcile Net Income Loss To Cash Provided By Used In Operating Activities [Abstract] Depreciation and amortization Depreciation Depletion And Amortization Amortization of premium on investment securities Investment Income Amortization Of Premium Stock-based compensation expense Share Based Compensation Revaluation of convertible preferred stock warrant liability Other Operating Activities Cash Flow Statement Unrealized (gain) loss on foreign currency forward contracts Derivative Instruments Not Designated As Hedging Instruments Gain Loss Net Changes in operating assets and liabilities: Increase Decrease In Operating Capital [Abstract] Receivables from collaborations Increase Decrease In Accounts Receivable Prepaid expenses and other current assets Increase Decrease In Prepaid Deferred Expense And Other Assets Other assets Increase Decrease In Other Operating Assets Accounts payable Increase Decrease In Accounts Payable Accrued compensation and employee benefits Increase Decrease In Employee Related Liabilities Accrued and other liabilities Increase Decrease In Accrued Liabilities And Other Operating Liabilities Deferred revenue Increase Decrease In Deferred Revenue Other long-term liabilities Increase Decrease In Other Noncurrent Liabilities Net cash used in operating activities Net Cash Provided By Used In Operating Activities Continuing Operations Investing activities Net Cash Provided By Used In Investing Activities [Abstract] Purchases of property and equipment Payments To Acquire Property Plant And Equipment Purchases of investments Payments To Acquire Investments Proceeds from sales of investments Proceeds From Sale Of Available For Sale Securities Proceeds from maturities of investments Proceeds From Maturities Prepayments And Calls Of Available For Sale Securities Net cash (used in) provided by investing activities Net Cash Provided By Used In Investing Activities Continuing Operations Financing activities Net Cash Provided By Used In Financing Activities [Abstract] Proceeds from issuance of common stock, including early exercise of stock options Proceeds From Issuance Of Common Stock Net cash provided by financing activities Net Cash Provided By Used In Financing Activities Continuing Operations Net (decrease) increase in cash and cash equivalents Cash And Cash Equivalents Period Increase Decrease Cash and cash equivalents at beginning of year Cash and cash equivalents at end of year Text Block [Abstract] Organization Nature Of Operations Summary of Significant Accounting Policies Basis Of Presentation And Significant Accounting Policies [Text Block] Fair Value Measurements Fair Value Disclosures [Text Block] Financial Instruments Financial Instruments Disclosure [Text Block] Derivative Instruments Derivative Instruments And Hedging Activities Disclosure [Text Block] Balance Sheet Component Disclosure [Text Block] Balance Sheet Components Balance Sheet Component Disclosure [Text Block] Collaboration and License Agreements Collaborative Arrangement Disclosure [Text Block] Stock Based Compensation Disclosure Of Compensation Related Costs Share Based Payments [Text Block] Net Loss per Share Attributable to Common Stockholders Earnings Per Share [Text Block] Basis of Presentation Consolidation Policy [Text Block] Use of Estimates Use Of Estimates Cash and Cash Equivalents Cash And Cash Equivalents Policy [Text Block] Investments Investment Policy [Text Block] Customer Concentration Concentration Risk Credit Risk Revenue Recognition Revenue Recognition Policy [Text Block] Foreign Currency Transactions and Hedging Derivatives Methods Of Accounting Nonhedging Derivatives Net Loss per Share Attributable to Common Stockholders Earnings Per Share Policy [Text Block] Revenue Accounted for 10% or More of Total Revenues Schedule Of Revenue By Major Customers By Reporting Segments Table [Text Block] Summary of Financial Assets, and Liabilities, Allocated into Level 1, Level 2, and Level 3 Measured on Recurring Basis Fair Value Assets Measured On Recurring Basis [Text Block] Cash Equivalents and Investments Classified as Available-for-sale Securities Schedule Of Available For Sale Securities Reconciliation Table [Text Block] Accrued Expenses Schedule Of Accrued Liabilities Table [Text Block] Collaborations [Text Block] Summary of Revenue from Collaboration and License Agreements Collaborations [Text Block] Summary of Option Activities Schedule Of Share Based Compensation Activity Table [Text Block] Fair Values of Employee Stock Options Schedule Of Share Based Payment Award Stock Options Valuation Assumptions Table [Text Block] Classification of Stock-Based Compensation Expense Schedule Of Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Text Block] Outstanding Shares of Common Stock Equivalents Excluded from Computation of Diluted Net Loss Schedule Of Antidilutive Securities Excluded From Computation Of Earnings Per Share [Text Block] Organization Consolidation And Presentation Of Financial Statements [Abstract] Organization And Nature Of Business [Line Items] Organization Consolidation And Presentation Of Financial Statements [Abstract] Organization And Nature Of Business [Table] Organization And Nature Of Business [Table] Organization And Nature Of Business [Table] Organization And Nature Of Business [Line Items] Organization And Nature Of Business [Line Items] Number of operating segment Number Of Operating Segments Risks And Uncertainties [Abstract] Risks And Uncertainties [Abstract] Concentration Risk [Table] Concentration Risk [Table] Concentration Risk Benchmark Concentration Risk By Benchmark [Axis] Concentration Risk Benchmark Concentration Risk Benchmark [Domain] Bristol Myers Squibb Company and Pfizer Inc [Member] Bristol-Myers Squibb Company ("BMS") and Pfizer Inc. ("Pfizer") Bristol Myers Squibb Company And Pfizer Inc [Member] Bayer Pharma Ag and Janssen Pharmaceuticals, Inc [Member] Bayer Pharma, AG ('Bayer") and Janssen Pharmaceuticals, Inc. ("Janssen") Bayer Pharma Ag And Janssen Pharmaceuticals Inc [Member] Daiichi sankyo inc. Daiichi Sankyo, Inc ("Daiichi") Daiichi Sankyo Inc [Member] Concentration Risk [Line Items] Concentration Risk [Line Items] Percentage of major customers revenue accounted for 10% or more of total revenues Concentration Risk Percentage1 Fair Value Disclosures [Abstract] Fair Value, Measurement Inputs, Disclosure [Line Items] Fair Value Disclosures [Abstract] Fair Value, Measurement Inputs, Disclosure [Table] Fair Value Measurement Inputs Disclosure [Table] Fair Value Measurement Inputs Disclosure [Table] Investment Type Investment Type [Axis] Investments Investment Type Categorization [Member] Money market funds Money Market Funds [Member] Commercial Paper and Corporate Securities [Member] Corporate notes and commercial paper Commercial Paper And Corporate Securities [Member] U.S. government agency securities U S Government Agencies Debt Securities [Member] Foreign currency forward contracts Foreign Exchange Forward [Member] Fair Value, Hierarchy Fair Value By Fair Value Hierarchy Level [Axis] Fair Value Hierarchy Fair Value Measurements Fair Value Hierarchy [Domain] Fair Value, Inputs, Level 1 Fair Value Inputs Level1 [Member] Fair Value, Inputs, Level 2 Fair Value Inputs Level2 [Member] Fair Value, Inputs, Level 3 Fair Value Inputs Level3 [Member] Fair Value Measurement Inputs Disclosure [Line Items] Fair Value Measurement Inputs Disclosure [Line Items] Financial Assets: Assets Fair Value Disclosure [Abstract] Fair value of financial assets measured on a recurring basis Assets Fair Value Disclosure Recurring Total financial assets Assets Fair Value Disclosure Investments Debt And Equity Securities [Abstract] Investments Debt And Equity Securities [Abstract] Schedule Of Available For Sale Securities [Table] Schedule Of Available For Sale Securities [Table] Cash equivalents Cash Equivalents [Member] Short-term investments Short Term Investments [Member] Long Term Investments [Member] Long-term investments Long Term Investments [Member] Schedule Of Available For Sale Securities [Line Items] Schedule Of Available For Sale Securities [Line Items] Cost Available For Sale Securities Amortized Cost Unrealized Gain Available For Sale Securities Gross Unrealized Gains Unrealized (Loss) Available For Sale Securities Gross Unrealized Loss Estimated Fair Value Available For Sale Securities Available for sale securities contractual maturity. Available For Sale Securities Contractual Maturity Available For Sale Securities Contractual Maturity Available-for-sale Securities, Gross Realized Gain (Loss) Available For Sale Securities Gross Realized Gain Loss Net Derivative Instruments And Hedging Activities Disclosure [Abstract] Derivative Instruments And Hedging Activities Disclosure [Abstract] Fair Values Derivatives Balance Sheet Location By Derivative Contract Type By Hedging Designation [Table] Fair Values Derivatives Balance Sheet Location By Derivative Contract Type By Hedging Designation [Table] Balance Sheet Location Balance Sheet Location [Axis] Balance Sheet Location Balance Sheet Location [Domain] Prepaid Expenses and Other Current Assets Prepaid Expenses And Other Current Assets [Member] Derivatives Fair Value [Line Items] Derivatives Fair Value [Line Items] Foreign currency forward contracts, notional amount Derivative Notional Amount Derivative assets Derivative Assets Foreign currency forward contracts unrealized gain (loss) Unrealized Gain Loss On Derivatives Foreign currency forward contracts recognized realized gain (loss) Gain Loss On Sale Of Derivatives Accrued Research And Development Expense. Payables And Accruals [Abstract] Accounts Payable and Accrued Liabilities [Line Items] Payables And Accruals [Abstract] Accounts Payable and Accrued Liabilities [Table] Accounts Payable And Accrued Liabilities [Table] Accounts Payable And Accrued Liabilities [Table] Accounts Payable And Accrued Liabilities [Line Items] Accounts Payable And Accrued Liabilities [Line Items] Research and development related Accrued Research And Development Expense Legal and accounting fees Accrued Professional Fees Current Deferred rent Deferred Rent Credit Current Other Other Liabilities Current Total accrued liabilities Accrued Liabilities And Other Liabilities Goodwill And Intangible Assets Disclosure [Abstract] Goodwill And Intangible Assets Disclosure [Abstract] Schedule Of Collaborative Arrangements And Noncollaborative Arrangement Transactions [Table] Schedule Of Collaborative Arrangements And Noncollaborative Arrangement Transactions [Table] Research and Development Arrangement, Contract to Perform for Others, Type Research And Development Arrangement Contract To Perform For Others By Type [Axis] Research and Development Arrangement, Contract to Perform for Others, Type Research And Development Arrangement Contract To Perform For Others Type [Domain] Licensing Agreements Licensing Agreements [Member] Customer Major Customers [Axis] Customer Name Of Major Customer [Domain] Lee's Pharmaceutical (HK) Ltd [Member] Lee's Pharmaceutical (HK) Ltd (“Lee's”) Lee Pharmaceutical Hk Ltd [Member] Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items] Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]