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Accrued Liabilities [Table Text Block] Reconciliation of cash, cash equivalents and restricted cash: Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents [Abstract] Defined contribution plan, employer discretionary contribution amount Defined Contribution Plan, Employer Discretionary Contribution Amount Operating lease right-of-use asset Deferred Tax Liabilities, Operating Lease, Right-Of-Use Asset Deferred Tax Liabilities, Operating Lease, Right-Of-Use Asset Subsequent Event [Table] Subsequent Event [Table] Vested Shares Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Vested in Period Entity Tax Identification Number Entity Tax Identification Number Number of shares authorized Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Authorized Total gross deferred tax liabilities Deferred Tax Liabilities, Gross Revenue from Contract with Customer [Line Items] Revenue from Contract with Customer [Abstract] Shares witheld for taxes for vesting of restricted stock units (in shares) Share-Based Payment Arrangement, Shares Withheld for Tax Withholding Obligation Letters Of Credit Receivable, Current Letters Of Credit Receivable, Current Letters Of Credit Receivable, Current Schedule of Effective Income Tax Rate Reconciliation Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] Decrease in cash, cash equivalents and restricted cash Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect Restricted Cash Cash and Cash Equivalents Disclosure [Text Block] Commercial paper Commercial Paper [Member] Entity Central Index Key Entity Central Index Key Antidilutive Securities, Name [Domain] Antidilutive Securities, Name [Domain] Measurement Frequency [Axis] Measurement Frequency [Axis] Research and Development Costs Research and Development Expense, Policy [Policy Text Block] Weighted Average Grant Date Fair Value Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] Shares withheld for taxes for vesting of restricted stock units Share-Based Payment Arrangement, Decrease for Tax Withholding Obligation Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-Based Compensation Arrangements by Share-Based Payment Award [Table] UCB Option and License Agreement Collaborative Arrangement Disclosure [Text Block] Concentrations of Credit Risk and Significant Suppliers and License Agreements Concentration Risk, Credit Risk, Policy [Policy Text Block] Accrued other expenses Other Accrued Liabilities, Current City Area Code City Area Code General and administrative General and Administrative Expense Assets Assets [Abstract] Retirement Benefits [Abstract] Other debt securities Other Debt Obligations [Member] Other Commitments [Line Items] Other Commitments [Line Items] Stockholders’ equity: Statement of Stockholders' Equity [Abstract] Sale of Stock [Axis] Sale of Stock [Axis] Cash flows from financing activities: Net Cash Provided by (Used in) Financing Activities [Abstract] Asset Class [Axis] Asset Class [Axis] Net Loss per Share Earnings Per Share, Policy [Policy Text Block] Stock-based compensation expense Share-Based Payment Arrangement, Noncash Expense Weighted average grant-date fair value per share Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value Purchases of property and equipment Payments to Acquire Property, Plant, and Equipment Research and development Research and Development Expense Research and Development Expense [Member] Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Operating lease right-of-use assets obtained in exchange for operating lease liabilities Right-of-Use Asset Obtained in Exchange for Operating Lease Liability