CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Beginning Balance at Dec. 31, 2014	$ 1,245,192	$ 388	$ 16,480	$ 1,278,528	$ (50,204)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Foreign currency translation adjustment	(51,060)				(51,060)
Net income (loss)	192,008			192,008
Comprehensive income	140,948
Options exercised and awards vested	2,170	0	2,170
Stock option expense	13,125		13,125
Excess tax benefits - stock options and awards	(1,172)		(1,172)
Repurchase of common stock	(75,805)	(10)	(30,603)	(45,192)
Ending Balance at Dec. 31, 2015	1,324,458	378	0	1,425,344	(101,264)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Foreign currency translation adjustment	(49,141)				(49,141)
Net income (loss)	93,221			93,221
Comprehensive income	44,080
Options exercised and awards vested	2,206	1	2,205
Stock option expense	12,217		12,217
Excess tax benefits - stock options and awards	(2,241)		(2,241)
Repurchase of common stock	(24,234)	(4)	(6,713)	(17,517)
Other	(62)	0	0	(60)	(2)
Ending Balance at Dec. 31, 2016	1,356,424	375	5,468	1,500,988	(150,407)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Foreign currency translation adjustment	24,117			0	24,117
Net income (loss)	(100,639)			(100,639)
Comprehensive income	(76,522)
Options exercised and awards vested	560		560
Stock option expense	14,270	0	14,270	0	0
Other	(271)	(3)	(215)	(53)	0
Ending Balance at Dec. 31, 2017	$ 1,294,461	$ 372	$ 20,083	$ 1,400,296	$ (126,290)