Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Income Tax Contingency [Line Items]
Provision for (benefit from) income taxes	$ (3,321)	$ 26,557	$ (5,959)	$ (8,722)
Loss before taxes	(31,577)	(12,500)	$ (67,232)	$ (58,808)
Effective tax rate (percent)			8.90%	14.80%
Unrecognized tax benefits	34,100	30,500	$ 34,100	$ 30,500
Unrecognized tax benefits that would impact the effective income tax rate	22,200	$ 24,000	22,200	$ 24,000
Interest and penalties related to unrecognized tax benefits	$ 700		$ 700		$ 600
Provisional tax expense					5,600
Remeasurement of U.S. deferred taxes					13,500
Federal Tax Credits and Remeasurement
Income Tax Contingency [Line Items]
Remeasurement of U.S. deferred taxes					$ 7,900