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Income Taxes - Additional Information (Detail) (USD $) | 12 Months Ended
--- | ---
Dec. 31, 2013 | Dec. 31, 2012
Income Tax Contingency [Line Items] |  |
Statutory income tax rate | 35.00% |
Increase in valuation allowance | $ 51,800,000 | $ 43,600,000
Valuation allowance related to stock-based compensation and exercises prior to the implementation of ASC 515 and 718 | 35,600,000 | 35,600,000
Deferred U.S. income taxes | 422,000 | (422,000)
Income taxes have not been provided on a cumulative total | 1,700,000 |
Federal orphan drug credits | 17,700,000 |
Federal orphan drug credits, expiration year | 2026 |
Unrecognized tax benefits, period may increase or decrease due to tax examination | Next twelve months |
Federal [Member] |  |
Income Tax Contingency [Line Items] |  |
Net operating loss carryforward for income tax | 1,029,700,000 |
Net operating loss carryforward, expiration year | 2018 |
Income tax research credits | 36,500,000 |
Income tax research credits, expiration year | 2019 |
State [Member] |  |
Income Tax Contingency [Line Items] |  |
Net operating loss carryforward for income tax | 614,600,000 |
Net operating loss carryforward, expiration year | 2014 |
Income tax research credits | $ 20,900,000 |

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