CONDENSED CONSOLIDATED STATEMENTSOF STOCKHOLDERS' EQUITY (UNAUDITED) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Losses
Beginning Balance at Dec. 31, 2017	$ 1,294,461	$ 372	$ 20,083	$ 1,400,296	$ (126,290)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Foreign currency translation adjustment	(8,545)				(8,545)
Net loss	(10,421)			(10,421)
Comprehensive loss	(18,966)
ASC 606	1,786			1,786
Repurchase of common stock	(9,830)	(2)		(9,828)
Options exercised	642	24	618
Stock option expense	7,585		7,585
Other	(231)		(137)	(94)
Ending Balance at Jun. 30, 2018	1,275,447	394	28,149	1,381,739	(134,835)
Beginning Balance at Mar. 31, 2018	1,305,109	381	23,964	1,393,933	(113,169)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Foreign currency translation adjustment	(21,666)				(21,666)
Net loss	(3,042)			(3,042)
Comprehensive loss	(24,708)
Repurchase of common stock	(9,830)	(2)		(9,828)
Options exercised	590	15	575
Stock option expense	3,611		3,611
Other	675		(1)	676
Ending Balance at Jun. 30, 2018	1,275,447	394	28,149	1,381,739	(134,835)
Beginning Balance at Dec. 31, 2018	1,096,162	376	34,953	1,205,946	(145,113)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Foreign currency translation adjustment	(690)				(690)
Net loss	(4,369)			(4,369)
Comprehensive loss	(5,059)
Repurchase of common stock	(1,996)			(1,996)
Stock option expense	8,083		8,083
Other	(62)		17	(79)
Ending Balance at Jun. 30, 2019	1,097,128	376	43,053	1,199,502	(145,803)
Beginning Balance at Mar. 31, 2019	1,095,405	376	39,815	1,198,700	(143,486)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Foreign currency translation adjustment	(2,317)				(2,317)
Net loss	1,681			1,681
Comprehensive loss	(636)
Repurchase of common stock	(880)			(880)
Stock option expense	3,221		3,221
Other	18		17	1
Ending Balance at Jun. 30, 2019	$ 1,097,128	$ 376	$ 43,053	$ 1,199,502	$ (145,803)