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, 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 income (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 income (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)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Retained earnings	1,181,023
Beginning Balance at Dec. 31, 2019	1,090,701	371	52,870	1,181,023	(143,563)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Foreign currency translation adjustment	(22,931)				(22,931)
Net income (loss)	(33,840)			(33,840)
Comprehensive loss	(56,771)
Repurchase of common stock	(25,000)	(8)		(24,992)
Stock option expense	6,458		6,458
Other	(1)		(1)
Ending Balance at Jun. 30, 2020	1,015,387	363	59,327	1,122,191	(166,494)
Beginning Balance at Mar. 31, 2020	1,024,201	363	56,045	1,136,335	(168,542)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Foreign currency translation adjustment	2,048				2,048
Net income (loss)	(14,142)			(14,142)
Comprehensive loss	(12,094)
Stock option expense	3,282		3,282
Other	(2)			(2)
Ending Balance at Jun. 30, 2020	1,015,387	$ 363	$ 59,327	$ 1,122,191	$ (166,494)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Retained earnings	$ 1,122,191