Income Taxes - Loss Before Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Domestic	$ (47,562)	$ (46,065)	$ (50,455)
Foreign	589	650	417
Net loss before provision for income taxes	$ (46,973)	$ (45,415)	$ (50,038)