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)		552,609
Stock issued on exercise/vesting of equity awards	1,778		1,778
Stock-based compensation	11,063		11,063
Acquisition of treasury stock (in shares)						(488,987)
Acquisition of treasury stock	(23,332)					$ (23,332)
Non-controlling interest	10						10
Other comprehensive loss	19,606				19,606
Net income	37,166			37,166
Ending balance (in shares) at Jun. 30, 2017		36,252,428				(2,560,697)
Ending balance at Jun. 30, 2017	579,922	$ 36	303,486	415,342	(55,451)	$ (83,694)	203
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)		792,409
Stock issued on exercise/vesting of equity awards	431	$ 1	430
Stock-based compensation	11,967		11,967
Acquisition of treasury stock (in shares)						(392,828)
Acquisition of treasury stock	(23,136)					$ (23,136)
Non-controlling interest	9						9
Other comprehensive loss	(41,911)				(41,911)
Net income	$ 37,620			37,620
Ending balance (in shares) at Jun. 30, 2018	34,288,314	37,583,160				(3,294,846)
Ending balance at Jun. 30, 2018	$ 585,479	$ 38	$ 334,643	$ 465,138	$ (87,621)	$ (126,952)	$ 233