Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2014	Dec. 31, 2015
Income Taxes [Line Items]
Net operating loss carryforwards	$ 100,790		$ 96,215
Research and development credit carryforwards	$ 34,845		$ 29,564
Net operating loss carryforwards, expiration date	2036
Net Operating loss Carryforwards resulting from excess tax deduction	$ 10,200
Increase (decrease) in deferred tax assets	19,000
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	$ 264,000
Net operating loss carryforwards, expiration date	2036
Federal and State
Income Taxes [Line Items]
Net operating loss carryforwards	$ 224,000