Income Taxes - Summary of Changes in Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits at beginning of year	$ 152,581	$ 47,109	$ 59,405
Increases resulting from tax positions taken during a prior period	7,482	110,894	3,456
Decreases resulting from tax positions taken during a prior period	(7,025)	(3,285)	(10,121)
Increases resulting from tax positions taken during the current period	1,656	817	3,447
Decreases related to settlements with taxing authorities	(3,594)	(123)	(7,481)
Reductions related to the lapse of statute of limitations	(19,492)	(2,831)	(1,597)
Unrecognized tax benefits at end of year	$ 131,608	$ 152,581	$ 47,109