Entity Central Index Key Document and entity information. Document And Entity Information [Abstract] 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 Escrow liability. Statement Of Financial Position [Abstract] Assets Assets [Abstract] Current assets: Assets Current [Abstract] Cash and cash equivalents Cash And Cash Equivalents At Carrying Value Marketable securities Available For Sale Securities Current Interest receivable Interest Receivable Current Accounts receivable Accounts Receivable Net Current Prepaid expenses Prepaid Expense Current Restricted cash Restricted Cash And Cash Equivalents At Carrying Value Other current assets Other Assets Current Total current assets Assets Current Marketable securities, non-current Available For Sale Securities Noncurrent Property and equipment, net Property Plant And Equipment Net Intangible assets, in-process research and development Indefinite Lived Intangible Assets Excluding Goodwill Goodwill Goodwill Other assets Other Assets Noncurrent Total assets Assets Liabilities and stockholders' equity Liabilities And Stockholders Equity [Abstract] Current liabilities: Liabilities Current [Abstract] Accounts payable and accrued liabilities Accounts Payable And Accrued Liabilities Current Accrued compensation and employee benefits Accrued Employee Benefits Current Escrow liability Escrow Liability Deferred revenues Deferred Revenue Current Total current liabilities Liabilities Current Deferred revenues, non-current Deferred Revenue Noncurrent Contingent consideration liability Business Combination Contingent Consideration Liability Noncurrent Deferred tax liability Deferred Income Tax Liabilities Total liabilities Liabilities Commitments and contingencies Commitments And Contingencies Stockholders' equity: Stockholders Equity [Abstract] Common stock, $0.01 par value; 160,000,000 and 80,000,000 shares authorized as of September 30, 2014 and December 31, 2013, respectively; 68,333,273 and 62,243,892 shares issued and outstanding at September 30, 2014 and December 31, 2013, respectively Common Stock Value Additional paid-in capital Additional Paid In Capital Common Stock 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 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 Revenue earned during the period from non-repayable sum of money awarded to an entity to carry out a specific purpose as provided in collaboration agreements. Income Statement [Abstract] Revenues: Revenues [Abstract] Collaboration agreements Collaboration Agreements Research grants Revenue From Grants Total revenues Revenues Operating expenses: Operating Expenses [Abstract] Research and development Research And Development Expense General and administrative General And Administrative Expense Change in fair value of contingent liability Business Combination Contingent Consideration Arrangements Change In Amount Of Contingent Consideration Liability1 Total operating expenses Operating Expenses Loss from operations Operating Income Loss Interest and other income, net Interest And Other Income Net loss Net Income Loss Basic and diluted net loss per share Earnings Per Share Basic And Diluted Shares used in computing basic and diluted net loss per share Weighted Average Number Of Share Outstanding Basic And Diluted Statement Of Income And Comprehensive Income [Abstract] Net loss Changes in unrealized gain on available-for-sale securities Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Net Of Tax Comprehensive loss Comprehensive Income Net Of Tax Net proceeds from issuance public offering. Statement Of Cash Flows [Abstract] Operating Activities: Net Cash Provided By Used In Operating Activities Continuing Operations [Abstract] Adjustments to reconcile net loss to net 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 marketable securities Accretion Amortization Of Discounts And Premiums Investments Stock-based compensation Share Based Compensation Change in fair value of contingent consideration liability Net changes in operating assets and liabilities: Increase Decrease In Operating Capital [Abstract] Interest receivable Increase Decrease In Accrued Interest Receivable Net Accounts receivable Increase Decrease In Accounts Receivable Prepaid expenses and other assets Increase Decrease In Prepaid Deferred Expense And Other Assets Accounts payable and accrued liabilities Increase Decrease In Accounts Payable And Accrued Liabilities Accrued compensation and employee benefits Increase Decrease In Employee Related Liabilities Deferred revenues Increase Decrease In Deferred Revenue 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 Continuing Operations [Abstract] Purchases of marketable securities Payments To Acquire Marketable Securities Maturities of marketable securities Proceeds From Sale And Maturity Of Marketable Securities Purchases of property and equipment Payments To Acquire Property Plant And Equipment Net cash provided by / (used in) investing activities Net Cash Provided By Used In Investing Activities Continuing Operations Financing Activities: Net Cash Provided By Used In Financing Activities Continuing Operations [Abstract] Proceeds from public offering of common stock, net of issuance costs Net Proceeds From Issuance Public Offering Proceeds from issuance of common stock Proceeds From Issuance Of Common Stock Net cash provided by financing activities Net Cash Provided By Used In Financing Activities Continuing Operations Net increase in cash and cash equivalents Cash And Cash Equivalents Period Increase Decrease Cash and cash equivalents, beginning of period Cash and cash equivalents, end of period Accounting Policies [Abstract] Basis of Presentation and Summary of Significant Accounting Policies Basis Of Presentation And Significant Accounting Policies [Text Block] Fair Value Disclosures [Abstract] Fair Value Measurements Fair Value Disclosures [Text Block] Investments Debt And Equity Securities [Abstract] Marketable Securities Investments In Debt And Marketable Equity Securities And Certain Trading Assets Disclosure [Text Block] Earnings Per Share [Abstract] Basic and Diluted Net Loss Per Share Earnings Per Share [Text Block] Organization Consolidation And Presentation Of Financial Statements [Abstract] Major Customers, Partnerships and Strategic Alliances Collaborative Arrangement Disclosure [Text Block] Goodwill And Intangible Assets Disclosure [Abstract] Intangible Assets Intangible Assets Disclosure [Text Block] Income Tax Disclosure [Abstract] Income Taxes Income Tax Disclosure [Text Block] Disclosure Of Compensation Related Costs Sharebased Payments [Abstract] Stock-Based Compensation Disclosure Of Compensation Related Costs Share Based Payments [Text Block] Equity [Abstract] Stockholders' Equity Stockholders Equity Note Disclosure [Text Block] Basis of Presentation Basis Of Accounting Policy Policy [Text Block] Use of Estimates Use Of Estimates Revenue Recognition Revenue Recognition Policy [Text Block] Recent Accounting Standards New Accounting Pronouncements Policy Policy [Text Block] Summary of Fair Value Measurements of Cash Equivalents, Available-for-Sale Securities and Contingent Consideration Liability Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Table [Text Block] Schedule of Changes in Estimated Fair Value of Contingent Consideration Liability Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Text Block] Schedule of Investments Available For Sale Securities [Text Block] Schedule Of Research And Development Arrangement Contract To Perform For Others [Table] Schedule Of Research And Development Arrangement Contract To Perform For Others [Table] Counterparty Name Counterparty Name [Axis] Counterparty Name Repurchase Agreement Counterparty Name [Domain] Biogen. Biogen [Member] Biogen [Member] Shire ag. Shire AG [Member] Shire Ag [Member] Sigma-Aldrich corporation. Sigma-Aldrich Corporation [Member] Sigma Aldrich Corporation [Member] Research and Development Arrangement, Contract to Perform for Others [Line Items] Research And Development Arrangement Contract To Perform For Others [Line Items] Revenues Recognized under Agreement Schedule Of Collaborative Arrangements And Noncollaborative Arrangement Transactions Table [Text Block] Carrying Values of Intangibles Assets Schedule Of Indefinite Lived Intangible Assets Table [Text Block] Stock-Based Compensation Expense Schedule Of Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Text Block] Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Table] Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Table] Major Types of Debt and Equity Securities Major Types Of Debt And Equity Securities [Axis] Major Types of Debt and Equity Securities Major Types Of Debt And Equity Securities [Domain] Money market funds [Member] Money Market Funds [Member] Commercial paper securities [Member] Commercial Paper [Member] Corporate debt securities [Member] Corporate Debt Securities [Member] U.S. government sponsored entity debt securities [Member] U S Government Sponsored Enterprises Debt Securities [Member] Contingent consideration liability. Contingent consideration liability [Member] Contingent Consideration Liability [Member] Fair Value, Hierarchy Fair Value By Fair Value Hierarchy Level [Axis] Fair Value Hierarchy Fair Value Measurements Fair Value Hierarchy [Domain] Level 1 [Member] Fair Value Inputs Level1 [Member] Level 2 [Member] Fair Value Inputs Level2 [Member] Level 3 [Member] Fair Value Inputs Level3 [Member] Investment Type Investment Type [Axis] Investments Investment Type Categorization [Member] Cash equivalents [Member] Cash Equivalents [Member] Marketable securities. Marketable securities [Member] Marketable Securities [Member] Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] Total cash equivalents Cash And Cash Equivalents Fair Value Disclosure Total marketable securities Marketable Securities Total cash equivalents and marketable securities Assets Fair Value Disclosure Total contingent consideration liabilities Liabilities Fair Value Disclosure Fair value as of December 31, 2013 Fair Value Measurement With Unobservable Inputs Reconciliations Recurring Basis Liability Value Change in fair value Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Liability Period Increase Decrease Fair value as of September 30, 2014 Schedule Of Available For Sale Securities [Table] Schedule Of Available For Sale Securities [Table] Available-for-sale securities [Member] Availableforsale Securities [Member] Schedule Of Available For Sale Securities [Line Items] Schedule Of Available For Sale Securities [Line Items] Amortized Cost Available For Sale Securities Amortized Cost Gross Unrealized Gains Available For Sale Securities Accumulated Gross Unrealized Gain Before Tax Gross Unrealized (Losses) Available For Sale Securities Accumulated Gross Unrealized Loss Before Tax Estimated Fair Value Available For Sale Securities Other-than-temporary impairments of investments Other Than Temporary Impairment Losses Investments Availableforsale Securities Schedule Of Antidilutive Securities Excluded From Computation Of Earnings Per Share [Table] Schedule Of Antidilutive Securities Excluded From Computation Of Earnings Per Share [Table] Antidilutive Securities Antidilutive Securities Excluded From Computation Of Earnings Per Share By Antidilutive Securities [Axis] Antidilutive Securities, Name Antidilutive Securities Name [Domain] Stock options [Member] Stock Option [Member] Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items] Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items] Stock options outstanding excluded in calculation of diluted net loss per share Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount Number of research program. Research And Development [Abstract] 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] Beta thalassemia. Beta-thalassemia [Member] Beta Thalassemia [Member] Sickle cell disease. Sickle cell disease [Member] Sickle Cell Disease [Member] Other projects. Other Projects Other Projects [Member] Legal Entity of Counterparty, Type Accounts Notes Loans And Financing Receivables By Legal Entity Of Counterparty Type [Axis] Legal Entity Type of Counterparty Legal Entity Type Of Counterparty [Domain] California institute for regenerative medicine. California Institute for Regenerative Medicine [Member] California Institute For Regenerative Medicine [Member] License agreement terms [Member] License Agreement Terms [Member] Number of research programs Number Of Research Program Milestone revenue receivable. Number of licensed products. Revenues under agreement Research And Development Arrangement Contract To Perform For Others Compensation Earned Milestone revenue receivable Milestone Revenue Receivable Number of licensed products approved under agreement Number Of Licensed Products Initial research term of agreement. Research program to develop laboratory research reagents Initial Research Term Of Agreement Deferred revenue Deferred Revenue Research service revenue under collaboration agreement. Deferred Revenue Arrangement Type Deferred Revenue Arrangement Type [Axis] Deferred Revenue Deferred Revenue Arrangement Type [Domain] Upfront Fee And Milestone Revenue Member Upfront Fee And Milestone Revenue Upfront Fee And Milestone Revenue [Member] Revenue related to Biogen Collaboration: Recognition of upfront fee License And Services Revenue Recognition of milestone Revenue Recognition Milestone Method Revenue Recognized Royalty revenues Royalty Revenue Research services Research Service Revenue Under Collaboration Agreement License fee and milestone revenues Licenses Revenue Total Contracts Revenue Aggregate number of gene targets. Number of initial gene targets. Number of gene targets.