Income Taxes - Summary of Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits, Excluding Interest and Penalties (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Balance, beginning of period	$ (34,970)	$ (53,952)	$ (57,116)
Additions for current year tax positions	(51,260)	(4,233)	(7,013)
Additions for prior year tax positions	(2,938)	(1,020)	(82)
Reductions for prior year tax positions	623	19,661	2,673
Reductions related to statute of limitation expirations	6,681	4,574	7,586
Balance, end of period	$ (81,864)	$ (34,970)	$ (53,952)