Fair Value Measurements - Contingent Consideration (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
Business Acquisition, Contingent Consideration [Line Items]
Beginning balance, Fair value of contingent consideration			$ 35,702	$ 56,463	$ 56,463
Change in fair value of contingent consideration	$ 11,300	$ (100)	(12,775)	$ 899	4,761
Earnout accretion			104		1,711
Payments and settlements	(100)		(751)		(30,924)
Foreign currency adjustment			(151)		(2,753)
Ending balance, Fair value of contingent consideration	$ 22,129		22,129		35,702
Generation Digital Solutions, Inc.
Business Acquisition, Contingent Consideration [Line Items]
Beginning balance, Fair value of contingent consideration			3,600
Ending balance, Fair value of contingent consideration					3,600
Escada
Business Acquisition, Contingent Consideration [Line Items]
Beginning balance, Fair value of contingent consideration			$ 2,049
Ending balance, Fair value of contingent consideration					2,049
Reggiani
Business Acquisition, Contingent Consideration [Line Items]
Escrow adjustment for Reggiani acquisition					(4,711)
Payments and settlements					$ (21,500)