Consolidated Statements of Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive (Loss)	Treasury Stock	Non - Controlling Interest
Adjustments for new accounting pronouncements | Impact of adoption of ASU 2016-09	$ 1,453		$ 5,999	$ (4,546)
Adjusted equity balance	533,631	$ 36	290,645	378,176	$ (75,057)	$ (60,362)	$ 193
Beginning balance (in shares) at Dec. 31, 2016		35,699,819				(2,071,710)
Beginning balance at Dec. 31, 2016	532,178	$ 36	284,646	382,722	(75,057)	$ (60,362)	193
Stock issued on exercise/vesting of equity awards (in shares)		825,873
Stock issued on exercise/vesting of equity awards/business acquisition	4,276	$ 1	4,275
Stock-based compensation	16,771		16,771
Acquisition of treasury stock (in shares)						(649,020)
Acquisition of treasury stock	(32,336)					$ (32,336)
Non-controlling interest	14						14
Other comprehensive loss	15,767				15,767
Net income	58,243			58,243
Ending balance (in shares) at Sep. 30, 2017		36,525,692				(2,720,730)
Ending balance at Sep. 30, 2017	596,366	$ 37	311,691	436,419	(59,290)	$ (92,698)	207
Adjustments for new accounting pronouncements | Impact of adoption of Topic 606	454			454
Adjusted equity balance	$ 600,499	$ 37	322,246	427,518	(45,710)	$ (103,816)	224
Beginning balance (in shares) at Dec. 31, 2017	33,888,733	36,790,751				(2,902,018)
Beginning balance at Dec. 31, 2017	$ 600,045	$ 37	322,246	427,064	(45,710)	$ (103,816)	224
Stock issued on exercise/vesting of equity awards (in shares)		913,223
Stock issued on exercise/vesting of equity awards/business acquisition	5,164	$ 1	5,163
Stock-based compensation	17,311		17,311
Acquisition of treasury stock (in shares)						(548,665)
Acquisition of treasury stock	(32,793)					$ (32,793)
Non-controlling interest	18						18
Other comprehensive loss	(68,620)				(68,620)
Net income	$ 52,869			52,869
Ending balance (in shares) at Sep. 30, 2018	34,253,291	37,703,974				(3,450,683)
Ending balance at Sep. 30, 2018	$ 574,448	$ 38	$ 344,720	$ 480,387	$ (114,330)	$ (136,609)	$ 242