Consolidated Statements of Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive (Loss)/Income	Treasury Stock	Non - Controlling Interest
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Impact of adoption of ASU 2016-09	$ 454		$ 0	$ 454
Adjusted equity balance	600,499	$ 37	322,246	427,518	$ (45,710)	$ (103,816)	$ 224
Beginning balance (in shares) at Dec. 31, 2017		36,790,751				(2,902,018)
Beginning balance at Dec. 31, 2017	600,045	$ 37	322,246	427,064	(45,710)	$ (103,816)	224
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock issued against stock-based compensation plans (in shares)		792,409
Stock issued against stock-based compensation plans	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 income	(41,911)				(41,911)
Net income	37,620			37,620
Ending balance (in shares) at Jun. 30, 2018		37,583,160				(3,294,846)
Ending balance at Jun. 30, 2018	585,479	$ 38	334,643	465,138	(87,621)	$ (126,952)	233
Beginning balance (in shares) at Mar. 31, 2018		37,568,973				(3,126,011)
Beginning balance at Mar. 31, 2018	601,705	$ 38	327,750	450,676	(59,670)	$ (117,320)	231
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock issued against stock-based compensation plans (in shares)		14,187
Stock issued against stock-based compensation plans	0
Stock-based compensation	6,893		6,893
Acquisition of treasury stock (in shares)						(168,835)
Acquisition of treasury stock	(9,632)					$ (9,632)
Non-controlling interest	2						2
Other comprehensive income	(27,951)				(27,951)
Net income	14,462			14,462
Ending balance (in shares) at Jun. 30, 2018		37,583,160				(3,294,846)
Ending balance at Jun. 30, 2018	$ 585,479	$ 38	334,643	465,138	(87,621)	$ (126,952)	233
Beginning balance (in shares) at Dec. 31, 2018	34,222,476	37,850,544				(3,628,068)
Beginning balance at Dec. 31, 2018	$ 618,319	$ 38	364,179	484,244	(83,467)	$ (146,925)	250
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock issued against stock-based compensation plans (in shares)		444,539
Stock issued against stock-based compensation plans	338		338
Stock-based compensation	14,111		14,111
Acquisition of treasury stock (in shares)						(460,691)
Acquisition of treasury stock	(27,538)					$ (27,538)
Allocation of equity component related to issuance costs on convertible senior notes	(13)		(13)
Purchase of non-controlling interest, net of its share of income	(232)		18				(250)
Other comprehensive income	9,109				9,109
Net income	$ 27,259			27,259
Ending balance (in shares) at Jun. 30, 2019	34,206,324	38,295,083				(4,088,759)
Ending balance at Jun. 30, 2019	$ 641,353	$ 38	378,633	511,503	(74,358)	$ (174,463)	0
Beginning balance (in shares) at Mar. 31, 2019		38,256,036				(3,890,599)
Beginning balance at Mar. 31, 2019	630,835	$ 38	371,144	498,939	(77,212)	$ (162,333)	259
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock issued against stock-based compensation plans (in shares)		39,047
Stock issued against stock-based compensation plans	316		316
Stock-based compensation	7,155		7,155
Acquisition of treasury stock (in shares)						(198,160)
Acquisition of treasury stock	(12,130)					$ (12,130)
Purchase of non-controlling interest, net of its share of income	(241)		18				(259)
Other comprehensive income	2,854				2,854
Net income	$ 12,564			12,564
Ending balance (in shares) at Jun. 30, 2019	34,206,324	38,295,083				(4,088,759)
Ending balance at Jun. 30, 2019	$ 641,353	$ 38	$ 378,633	$ 511,503	$ (74,358)	$ (174,463)	$ 0