CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated (Deficit) [Member]	Treasury Stock [Member]
Beginning balance at Dec. 31, 2016	$ 1,891,529	$ 10	$ 1,400,140	$ (4,695)	$ 522,436	$ (26,362)
Beginning balance, shares at Dec. 31, 2016		105,071,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	73,342				73,342
Exercise of stock options, shares		9,000
Exercise of stock options	184		184
Restricted stock grants, net, shares		549,000
Restricted stock grants, net	$ 6,619		6,619
Treasury Stock, Shares, Acquired	(201,306)	201,000
Restricted Stock Award, Forfeitures	$ 10,243					10,243
Other comprehensive (loss) income, net	7,546			7,546
Ending balance at Mar. 31, 2017	1,969,515	$ 10	1,406,943	2,851	596,316	(36,605)
Ending balance, shares at Mar. 31, 2017		105,428,000
Retained earnings	848,466
Beginning balance at Dec. 31, 2017	2,229,698	$ 10	1,424,540	(3,145)	848,466	(40,173)
Beginning balance, shares at Dec. 31, 2017		105,487,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	100,900				100,900
Exercise of stock options, shares		9,000
Exercise of stock options	215		215
Restricted stock grants, net, shares		546,000
Restricted stock grants, net	$ 6,705		6,705
Treasury Stock, Shares, Acquired	(180,867)	181,000
Restricted Stock Award, Forfeitures	$ 6,296					(6,296)
Other comprehensive (loss) income, net	(37,459)			(37,459)
Ending balance at Mar. 31, 2018	2,293,763	$ 10	$ 1,431,460	$ (41,662)	$ 950,424	$ (46,469)
Ending balance, shares at Mar. 31, 2018		105,861,000
Retained earnings	$ 950,424