Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands		12 Months Ended
	Dec. 22, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Loss Carryforwards [Line Items]
Current Income tax expense			$ 4,200
Current federal AMT Income tax expense			300
Current state Income tax expense			$ 3,900
Corporate tax rate			35.00%	35.00%	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%
Income tax benefit			$ 42,399	$ 13,224	$ 11,215
Income tax expense (benefit) in discontinued operations			46,600	$ 13,200	$ 11,200
Federal Orphan Drug Credits			$ 120,800
Federal orphan drug credits begin to expire			2031
Change in valuation allowance			$ 217,800
Tax cuts and jobs act of 2017 incomplete accounting change in valuation allowance net decrease			27,500
ASU No. 2016-09 [Member]
Operating Loss Carryforwards [Line Items]
Federal and state net operating loss carryforwards relate to deductions for stock option compensation			39,200
State [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards			$ 223,400
Net operating loss carryforwards expire year begin			2028
Net operating loss carryforwards expire year through			2036
State [Member] | Research and Development [Member]
Operating Loss Carryforwards [Line Items]
Amount of tax credit carryforward			$ 18,700
Tax credit carryforwards expire year begin			2022
Tax credit carryforwards expire year through			2026
State [Member] | Investment [Member]
Operating Loss Carryforwards [Line Items]
Amount of tax credit carryforward			$ 400
Tax credit carryforwards expire year begin			2018
Tax credit carryforwards expire year through			2020
State [Member] | ASU No. 2016-09 [Member]
Operating Loss Carryforwards [Line Items]
Federal and state net operating loss carryforwards relate to deductions for stock option compensation			$ 25,200
Federal [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards			$ 138,100
Net operating loss carryforwards expire year begin			2028
Net operating loss carryforwards expire year through			2036
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			2026
Scenario, Plan [Member]
Operating Loss Carryforwards [Line Items]
Corporate tax rate		21.00%