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	7,222				7,222
Employee stock options, restricted stock and employee stock purchase plan	654	0	353		(90)	391
Stock-based compensation expense	2,289		2,289
Foreign currency translation, net of tax	(666)			(666)
Ending balance at Mar. 31, 2018	550,215	1,046	606,491	(53,885)	123,743	(127,180)
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	1,282				1,282
Employee stock options, restricted stock and employee stock purchase plan	790	0	309		0	481
Stock-based compensation expense	4,969		4,969
Treasury shares purchased at cost	(5,013)					(5,013)
Foreign currency translation, net of tax	(1,921)			(1,921)
Ending balance at Mar. 31, 2019	$ 569,788	$ 1,064	$ 622,554	$ (69,594)	$ 150,084	$ (134,320)