Change in the Amount of Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Unrecognized tax benefit, beginning balance		$ 11,380	$ 11,777	$ 15,314
Increases for tax positions related to the current year		990	733	600
Decreases for tax positions related to prior years	$ (4,000)	(205)	(16)	0
Increases for tax positions related to prior years		153	104	50
Decreases relating to settlements with taxing authorities		0	0	(3,805)
Increases acquired in business acquisitions		0	617	0
Foreign currency translation		10	(1)	(24)
Reductions due to lapsed statute of limitations		(334)	(1,834)	(358)
Unrecognized tax benefit, ending balance		$ 11,994	$ 11,380	$ 11,777