Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Paid-In Capital	Accumulated Other Comprehensive Loss	Retained Earnings	Treasury Stock
Beginning balance at Dec. 31, 2017	$ 547,480	$ 1,046	$ 603,849	$ (53,219)	$ 123,375	$ (127,571)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	21,712				21,712
Employee stock options, restricted stock and employee stock purchase plan	774	17	3,005		(90)	(2,158)
Stock-based compensation expense	8,497		8,497
Foreign currency translation, net of tax	(11,548)			(11,548)
Ending balance at Sep. 30, 2018	560,151	1,063	615,351	(64,767)	138,233	(129,729)
Beginning balance at Jun. 30, 2018	554,723	1,061	611,667	(63,097)	134,589	(129,497)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	3,644				3,644
Employee stock options, restricted stock and employee stock purchase plan	(195)	2	35			(232)
Stock-based compensation expense	3,649		3,649
Foreign currency translation, net of tax	(1,670)			(1,670)
Ending balance at Sep. 30, 2018	560,151	1,063	615,351	(64,767)	138,233	(129,729)
Beginning balance at Dec. 31, 2018	569,681	1,064	617,276	(67,673)	148,802	(129,788)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	4,147				4,147
Employee stock options, restricted stock and employee stock purchase plan	(444)	3	(8,019)		(1,646)	9,218
Stock-based compensation expense	9,375		9,375
Treasury shares purchased at cost	(19,031)					(19,031)
Foreign currency translation, net of tax	(4,097)			(4,097)
Ending balance at Sep. 30, 2019	559,631	1,067	618,632	(71,770)	151,303	(139,601)
Beginning balance at Jun. 30, 2019	566,129	1,067	618,626	(67,873)	153,395	(139,086)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(1,441)				(1,441)
Employee stock options, restricted stock and employee stock purchase plan	(167)		(2,495)		(651)	2,979
Stock-based compensation expense	2,501		2,501
Treasury shares purchased at cost	(3,494)					(3,494)
Foreign currency translation, net of tax	(3,897)			(3,897)
Ending balance at Sep. 30, 2019	$ 559,631	$ 1,067	$ 618,632	$ (71,770)	$ 151,303	$ (139,601)