Reconciliation of Beginning and Ending Amount of Gross Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at January 1,	$ 56,721	$ 50,337
Increase based upon tax positions of current year	1,183	5,955
(Decrease) increase based upon tax positions of a prior year		217
Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions	(6,839)
Unrecognized Tax Benefits, Increase Resulting from Acquisition	0	1,810
Unrecognized tax benefits, decrease due to changes in tax rates	(3,408)	0
Decrease based upon settlements with taxing authorities	(2,191)	(1,159)
Decrease based upon a lapse in the statute of limitations	(320)	(439)
Balance at December 31,	$ 45,146	$ 56,721