Income Taxes - Components of Loss Before Income Tax Expense (Benefit) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest [Abstract]
Domestic	$ (125,770)	$ (83,714)	$ (47,428)
Foreign	(5,541)	(4,457)	(3,281)
Loss before income tax expense (benefit)	$ (131,311)	$ (88,171)	$ (50,709)