Consolidated Statements Of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings (Accumulated Deficit) [Member]
Shareholders' Equity, shares at Dec. 31, 2013		381,300,000
Shareholders' Equity at Dec. 31, 2013	$ 4,648,952	$ 3,813	$ 3,052,016	$ (795)	$ 1,593,918
Stock option exercises, shares		1,422,000
Stock option exercises	15,627	$ 14	15,613	0	0
Share issuances, net of cancellations, shares		(43,000)
Dividends declared	(86,370)		72		(86,442)
Share repurchases, shares		(13,220,000)
Share repurchases	(253,019)	$ (132)			(252,887)
Share-based compensation	13,812	$ 0	13,786	0	26
Excess tax benefits (deficiencies) from share-based compensation	(8,491)		(8,491)
Net income	474,338				474,338
Other comprehensive income	105			105
Shareholders' Equity, shares at Dec. 31, 2014		369,459,000
Shareholders' Equity at Dec. 31, 2014	4,804,954	$ 3,695	3,072,996	(690)	1,728,953
Stock option exercises, shares		904,000
Stock option exercises	10,534	$ 9	10,525	0	0
Share issuances, net of cancellations, shares		428,000
Share issuances, net of cancellations	7,424	$ 4	7,420
Dividends declared	(117,873)		8		(117,881)
Share repurchases, shares		(21,642,000)
Share repurchases	(442,738)	$ (217)			(442,521)
Share-based compensation	16,888	$ 0	16,888	0	0
Excess tax benefits (deficiencies) from share-based compensation	(14,035)		(14,035)
Net income	494,090				494,090
Other comprehensive income	$ 81			81
Shareholders' Equity, shares at Dec. 31, 2015	349,148,351	349,149,000
Shareholders' Equity at Dec. 31, 2015	$ 4,759,325	$ 3,491	3,093,802	(609)	1,662,641
Stock option exercises, shares		498,000
Stock option exercises	5,845	$ 5	5,840	0	0
Share issuances, net of cancellations, shares		530,000
Share issuances, net of cancellations	8,856	$ 5	8,851
Dividends declared	(122,240)		0		(122,240)
Share repurchases, shares		(31,087,000)
Share repurchases	(603,206)	$ (310)			(602,896)
Share-based compensation	18,626	$ 0	18,626	0	0
Excess tax benefits (deficiencies) from share-based compensation	(10,629)		(10,629)
Net income	602,703				602,703
Other comprehensive income	$ 83			83
Shareholders' Equity, shares at Dec. 31, 2016	319,089,720	319,090,000
Shareholders' Equity at Dec. 31, 2016	$ 4,659,363	$ 3,191	$ 3,116,490	$ (526)	$ 1,540,208