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)		4
Stock option exercises	52	$ 0	52
Stock issuances, net of cancellations (shares)		456
Stock issuances, net of cancellations	8,856	$ 4	8,852
Dividends declared	(31,459)		0		(31,459)
Share repurchases	(52,745)	$ (32)			(52,713)
Share repurchases (shares)		(3,226)
Share-based compensation	6,635		6,635
Excess tax benefits (deficiencies) from share-based awards	(458)		(458)
Net income	83,300				83,300
Other comprehensive income	21			21
Shareholders' Equity end of period at Mar. 31, 2016	4,773,527	$ 3,463	3,108,883	(588)	1,661,769
Shareholders' Equity, shares end of period (shares) at Mar. 31, 2016		346,383
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)		961
Stock option exercises	11,118	$ 10	11,108
Stock issuances, net of cancellations (shares)		677
Stock issuances, net of cancellations	3,566	$ 10	3,556
Dividends declared	(28,838)				(28,838)
Share repurchases	(105,522)	$ (50)			(105,472)
Share repurchases (shares)		(4,696)
Share-based compensation	10,682		10,682
Net income	91,518				91,518
Other comprehensive income	21			21
Shareholders' Equity end of period at Mar. 31, 2017	$ 4,660,145	$ 3,161	$ 3,141,430	$ (505)	$ 1,516,059
Shareholders' Equity, shares end of period (shares) at Mar. 31, 2017		316,032