CONDENSED CONSOLIDATED STATEMENTS OF 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	(14,111)				(14,111)
Net loss	(20,783)			(20,783)
Total comprehensive loss	(34,894)
ASC 606	1,786			1,786
Repurchase of common stock	(80,937)	(2)		(80,935)
Options exercised and awards vested, net of shares withheld for employee taxes	1,130	24	1,106
Stock option expense	9,950		9,950
Other	(240)		(137)	(103)
Ending Balance at Sep. 30, 2018	1,191,256	394	31,002	1,300,261	(140,401)
Beginning Balance at Jun. 30, 2018	1,275,447	394	28,149	1,381,739	(134,835)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Foreign currency translation adjustment	(5,566)				(5,566)
Net loss	(10,358)			(10,358)
Total comprehensive loss	(15,924)
Repurchase of common stock	(71,107)			(71,107)
Options exercised and awards vested, net of shares withheld for employee taxes	488		488
Stock option expense	2,366		2,366
Other	(14)		(1)	(13)
Ending Balance at Sep. 30, 2018	1,191,256	394	31,002	1,300,261	(140,401)
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	(10,311)				(10,311)
Net loss	(5,679)			(5,679)
Total comprehensive loss	(15,990)
Repurchase of common stock	(5,365)	(1)		(5,364)
Options exercised and awards vested, net of shares withheld for employee taxes	2,182	1	2,181
Stock option expense	15,746		15,746
Other	(63)		16	(79)
Ending Balance at Sep. 30, 2019	1,092,672	376	52,896	1,194,824	(155,424)
Beginning Balance at Jun. 30, 2019	1,097,128	376	43,053	1,199,502	(145,803)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Foreign currency translation adjustment	(9,621)				(9,621)
Net loss	(1,310)			(1,310)
Total comprehensive loss	(10,931)
Repurchase of common stock	(3,368)	(1)		(3,367)
Options exercised and awards vested, net of shares withheld for employee taxes	2,182	1	2,181
Stock option expense	7,663		7,663
Other	(2)		(1)	(1)
Ending Balance at Sep. 30, 2019	$ 1,092,672	$ 376	$ 52,896	$ 1,194,824	$ (155,424)