Income Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013
Operating Loss Carryforwards [Line Items]
Convertible senior notes, percentage	4.50%
Federal and state net operating loss carryforwards relate to deductions for stock option compensation	$ 11.6
Federal Orphan Drug Credits	14.4
Federal [Member]
Operating Loss Carryforwards [Line Items]
NOL	304.2
Federal [Member] | Research and Development [Member]
Operating Loss Carryforwards [Line Items]
Amount of tax credit carryforward	18.6
State [Member]
Operating Loss Carryforwards [Line Items]
NOL	230.7
State [Member] | Research and Development [Member]
Operating Loss Carryforwards [Line Items]
Amount of tax credit carryforward	6.3
State [Member] | Investment [Member]
Operating Loss Carryforwards [Line Items]
Amount of tax credit carryforward	$ 0.3