Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Taxes [Line Items]
Net operating loss carryforwards		$ 89,098	$ 100,790
Research and development credit carryforwards		$ 32,395	34,845
Net operating loss carryforwards, expiration date		2037
Accumulated excess tax benefit recognised as deferred tax asset		$ 0	$ 0
Increase (decrease) in deferred tax assets		$ (48,400)
Effective income tax rate		34.00%	34.00%	34.00%
ASU 2016-09
Income Taxes [Line Items]
Accumulated excess tax benefit recognised as deferred tax asset			$ 10,200
Accumulated Deficit | ASU 2016-09
Income Taxes [Line Items]
Cumulative-effect adjustment from adoption of ASU 2016-09			$ 122
Tax Cuts And Jobs Act of 2017
Income Taxes [Line Items]
Effective income tax rate		35.00%
Change in tax rate in income tax expense benefit		$ 67,000
Tax Cuts And Jobs Act of 2017 | Scenario, Forecast
Income Taxes [Line Items]
Effective income tax rate	21.00%
Research Tax Credit Carryforward
Income Taxes [Line Items]
Research and development credit carryforwards		35,000
Net Operating Loss Carryforwards
Income Taxes [Line Items]
Increase (decrease) in deferred tax assets					$ (11,200)
General Business Credits
Income Taxes [Line Items]
Increase (decrease) in deferred tax assets					$ (636)
Domestic Tax Authority
Income Taxes [Line Items]
Net operating loss carryforwards		$ 342,000
Net operating loss carryforwards, expiration date		2037
Federal and State
Income Taxes [Line Items]
Net operating loss carryforwards		$ 299,000