CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common stock	Paid-in capital	Treasury stock	Accumulated other comprehensive loss	Retained earnings (deficit)
Balance, beginning of year at Dec. 31, 2014		$ 340,047	$ 1,663,592	$ (32,937)	$ (81,341)	$ (852,458)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net common stock issued under share-based compensation plans		50	(478)
Reissuance of treasury stock, net under share-based compensation plans			(6,894)	29,575		(29,495)
Tax benefit from share-based compensation			2,116
Equity compensation			11,902
Other comprehensive income (loss)	$ 20,461				20,461
Net income	1,172,000					1,172,000
Balance, end of year at Dec. 31, 2015	2,236,140	340,097	1,670,238	(3,362)	(60,880)	290,047
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock		18,313	113,146
Net common stock issued under share-based compensation plans		990	(6,020)
Reissuance of treasury stock, net under share-based compensation plans			(130)	130
Tax benefit from share-based compensation			67
Equity compensation			11,373
Reacquisition of convertible junior subordinated debentures-equity component			(6,337)
Purchases of common stock	(147,100)			(147,127)
Other comprehensive income (loss)	(14,220)				(14,220)
Net income	342,517					342,517
Balance, end of year at Dec. 31, 2016	2,548,842	359,400	1,782,337	(150,359)	(75,100)	632,564
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of share-based compensation accounting standard update			49			153
Issuance of common stock		10,386	60,903
Net common stock issued under share-based compensation plans		781	(7,602)
Equity compensation			14,895
Reissuance of treasury stock, net				150,359		(21,740)
Other comprehensive income (loss)	41,739				41,739
Net income	355,761					355,761
Cumulative effect to reclassify certain tax effects from accumulated other comprehensive loss					(10,422)	10,422
Balance, end of year at Dec. 31, 2017	$ 3,154,526	$ 370,567	$ 1,850,582	$ 0	$ (43,783)	$ 977,160