Consolidated Statements Of Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings
Shareholders' Equity beginning of period at Dec. 31, 2015	$ 4,759,325	$ 3,491	$ 3,093,802	$ (609)	$ 1,662,641
Shareholders' Equity, shares beginning of period (shares) at Dec. 31, 2015		349,149
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock option exercises (shares)		67
Stock option exercises	742	$ 0	742
Stock issuances, net of cancellations (shares)		499
Stock issuances, net of cancellations	8,856	$ 5	8,851
Dividends declared	(62,747)				(62,747)
Share repurchases	(100,806)	$ (58)			(100,748)
Share repurchases (shares)		(5,819)
Share-based compensation	12,209		12,209
Excess tax benefits (deficiencies) from share-based awards	(563)		(563)
Net income	201,060				201,060
Other comprehensive income	41			41
Shareholders' Equity end of period at Jun. 30, 2016	4,818,117	$ 3,438	3,115,041	(568)	1,700,206
Shareholders' Equity, shares end of period (shares) at Jun. 30, 2016		343,896
Cumulative Effect on Retained Earnings, Net of Tax	18,237		(406)		18,643
Shareholders' Equity beginning of period at Dec. 31, 2016	4,659,363	$ 3,191	3,116,490	(526)	1,540,208
Shareholders' Equity, shares beginning of period (shares) at Dec. 31, 2016		319,090
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock option exercises (shares)		1,378
Stock option exercises	15,966	$ 14	15,952
Stock issuances, net of cancellations (shares)		729
Stock issuances, net of cancellations	3,564	$ 10	3,554
Dividends declared	(56,941)				(56,941)
Share repurchases	(405,819)	$ (178)			(405,641)
Share repurchases (shares)		(17,498)
Share-based compensation	17,323		17,323
Net income	192,268				192,268
Other comprehensive income	41			41
Shareholders' Equity end of period at Jun. 30, 2017	$ 4,444,002	$ 3,037	$ 3,152,913	$ (485)	$ 1,288,537
Shareholders' Equity, shares end of period (shares) at Jun. 30, 2017		303,699