Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Contingency [Line Items]
Increase (decrease) in valuation allowance	$ (98,400)	$ 60,800
Total gross deferred tax assets	11,070	109,865
Net operating loss carryforward	306,000
Tax credit carryforward	39,500
Unrecognized tax benefits	72	3,934	$ 10,116
Decrease in prior year unrecognized tax benefits	$ 3,934	$ 7,776
Federal tax benefit at statutory rate	21.00%	34.00%
Provisional amount related to re-measurement of deferred tax balance, reduction amount	$ 33,000
Tax Cuts and Jobs Act, Accounting complete	true
Federal [Member]
Income Tax Contingency [Line Items]
Net operating loss carryforwards	$ 11,100
Net operating loss carryforwards not subject to expiration	4,300
Net operating loss carryforwards subject to expire	$ 6,800
Operating loss carryforwards, expiration	Begin to expire in 2037
Federal [Member] | Research and Development Tax Credits [Member]
Income Tax Contingency [Line Items]
Tax credits	$ 200
Tax credit, expiration	Begin to expire in 2037