Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating Loss Carryforwards [Line Items]
Income tax expense (benefit)	$ 0	$ 0	$ 0
Charitable contribution carryforwards, pre tax	98
Government research and development tax credits	3,930	2,237
Unrecognized tax benefits	0	$ 0
Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	105,051
State
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 106,671
Minimum
Operating Loss Carryforwards [Line Items]
Charitable contribution carryforwards, expiration date	Dec. 31, 2017
Government research and development tax credits, expiration date	Dec. 31, 2028
Minimum | Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards, expiration date	Dec. 31, 2028
Minimum | State
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards, expiration date	Dec. 31, 2023