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