Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands		12 Months Ended
	Dec. 22, 2017	Dec. 31, 2018	Dec. 31, 2017
Operating Loss Carryforwards [Line Items]
Current income tax expense (benefit)		$ (100)	$ 4,200
Current federal AMT Income tax expense			300
Current state Income tax expense			$ 3,900
Corporate tax rate		21.00%	35.00%
Tax cuts and jobs act of 2017, accounting complete	false
Tax cuts and jobs act of 2017 percentage of tax deduction for interest expense and net operating losses of current year taxable income			80.00%
Receipt of milestone payments related to asset sale		$ 28,000	$ 580,714
Current federal and state income tax liability		400
AMT credit fund		500
Income tax benefit		7,695	42,399
Discontinued operation tax effect of discontinued operation		7,600	$ 46,600
Federal Orphan Drug Credits		$ 122,500
Federal orphan drug credits begin to expire		2031
State [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards		$ 263,900
Net operating loss carryforwards expire year begin		2031
State [Member] | Research and Development [Member]
Operating Loss Carryforwards [Line Items]
Amount of tax credit carryforward		$ 18,900
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		2019
Federal [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards		$ 179,700
Net operating loss carryforwards expire year begin		2031
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
Scenario, Plan [Member]
Operating Loss Carryforwards [Line Items]
Corporate tax rate		21.00%