Summary of Benefit from Income Taxes and Discrete Tax Items (Detail) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Tax Rate Reconciliation [Line Items]
Benefit from income taxes	[1]	$ (8,589)	$ (8,501)	$ (23,692)	$ (9,009)
Effective income tax rate				80.00%	(18.00%)

[1] On January 1, 2018, the Company adopted the ASC 606 revenue recognition standard and has adjusted prior periods to conform. See Note 2. "New Accounting Pronouncements" for additional information.