Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Operating Loss Carryforwards [Line Items]
Income tax benefit (expense)	$ (14)	$ 1,473
Discontinued operation tax effect of discontinued operation		$ 1,100
Federal orphan drug credits	$ 122,700
Federal orphan drug credits begin to expire	2031
State [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 292,200
Net operating loss carryforwards expire year begin	2033
State [Member] | Research and Development [Member]
Operating Loss Carryforwards [Line Items]
Amount of tax credit carryforward	$ 20,300
Tax credit carryforwards expire year begin	2022
Tax credit carryforwards expire year through	2025
State [Member] | Investment [Member]
Operating Loss Carryforwards [Line Items]
Amount of tax credit carryforward	$ 100
Tax credit carryforwards expire year begin	2020
Federal [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 206,800
Net operating loss carryforwards expire year begin	2033
Federal [Member] | Research and Development [Member]
Operating Loss Carryforwards [Line Items]
Amount of tax credit carryforward	$ 28,800
Tax credit carryforwards expire year begin	2022
Tax credit carryforwards expire year through	2025
Maximum [Member]
Operating Loss Carryforwards [Line Items]
Income tax benefit (expense)	$ (100)