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, shares beginning of period (shares) at Dec. 31, 2017		286,752
Shareholders' Equity beginning of period at Dec. 31, 2017	$ 4,154,026	$ 2,868	$ 3,171,542	$ (445)	$ 980,061
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of accounting change			0
Stock option exercises (shares)		284
Stock option exercises	2,723	$ 3	2,720
Stock issuances, net of cancellations (shares)		783
Stock issuances, net of cancellations	3,485	$ 8	3,477
Dividends declared	(26,051)				(26,051)
Share repurchases (shares)		(1,941)
Share repurchases	(59,491)	$ (20)	0		(59,471)
Share-based compensation	6,782		6,782
Net income	170,751				170,751
Other comprehensive income	21			21
Shareholders' Equity, shares end of period (shares) at Mar. 31, 2018		285,878
Shareholders' Equity end of period at Mar. 31, 2018	4,274,657	$ 2,859	3,184,521	(424)	1,087,701
Shareholders' Equity, shares beginning of period (shares) at Dec. 31, 2017		286,752
Shareholders' Equity beginning of period at Dec. 31, 2017	4,154,026	$ 2,868	3,171,542	(445)	980,061
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared	(52,000)
Net income	494,841
Other comprehensive income	50
Shareholders' Equity, shares end of period (shares) at Jun. 30, 2018		284,362
Shareholders' Equity end of period at Jun. 30, 2018	4,526,712	$ 2,843	3,191,087	(395)	1,333,176
Shareholders' Equity, shares beginning of period (shares) at Mar. 31, 2018		285,878
Shareholders' Equity beginning of period at Mar. 31, 2018	4,274,657	$ 2,859	3,184,521	(424)	1,087,701
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock option exercises (shares)		150
Stock option exercises	1,744	$ 1	1,743
Stock issuances, net of cancellations (shares)		87
Stock issuances, net of cancellations	(2)		(2)
Dividends declared	(25,915)				(25,915)
Share repurchases (shares)		(1,753)
Share repurchases	(53,000)	$ (17)	(284)		(52,699)
Share-based compensation	5,109		5,109
Net income	324,089				324,089
Other comprehensive income	30			30
Shareholders' Equity, shares end of period (shares) at Jun. 30, 2018		284,362
Shareholders' Equity end of period at Jun. 30, 2018	4,526,712	$ 2,843	3,191,087	(395)	1,333,176
Shareholders' Equity, shares beginning of period (shares) at Dec. 31, 2018		277,110
Shareholders' Equity beginning of period at Dec. 31, 2018	4,817,782	$ 2,771	3,201,427	(345)	1,613,929
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock option exercises (shares)		118
Stock option exercises	1,445	$ 1	1,444
Stock issuances, net of cancellations (shares)		1,337
Stock issuances, net of cancellations	5,804	$ 12	5,792
Dividends declared	(30,831)				(30,831)
Share repurchases (shares)		(1,309)
Share repurchases	(35,353)	$ (13)			(35,340)
Share-based compensation	7,810		7,810
Net income	166,757				166,757
Other comprehensive income	25			25
Shareholders' Equity, shares end of period (shares) at Mar. 31, 2019		277,256
Shareholders' Equity end of period at Mar. 31, 2019	4,933,439	$ 2,771	3,216,473	(320)	1,714,515
Shareholders' Equity, shares beginning of period (shares) at Dec. 31, 2018		277,110
Shareholders' Equity beginning of period at Dec. 31, 2018	4,817,782	$ 2,771	3,201,427	(345)	1,613,929
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared	(61,500)
Net income	407,798
Other comprehensive income	50
Shareholders' Equity, shares end of period (shares) at Jun. 30, 2019		274,975
Shareholders' Equity end of period at Jun. 30, 2019	5,069,807	$ 2,750	3,225,874	(295)	1,841,478
Shareholders' Equity, shares beginning of period (shares) at Mar. 31, 2019		277,256
Shareholders' Equity beginning of period at Mar. 31, 2019	4,933,439	$ 2,771	3,216,473	(320)	1,714,515
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock option exercises (shares)		316
Stock option exercises	3,763	$ 3	3,760
Stock issuances, net of cancellations (shares)		26
Stock issuances, net of cancellations		$ 2	(2)
Dividends declared	(30,633)				(30,633)
Share repurchases (shares)		(2,623)
Share repurchases	(83,471)	$ (26)			(83,445)
Share-based compensation	5,642		5,642
Net income	241,041				241,041
Other comprehensive income	25			25
Shareholders' Equity, shares end of period (shares) at Jun. 30, 2019		274,975
Shareholders' Equity end of period at Jun. 30, 2019	$ 5,069,807	$ 2,750	$ 3,225,874	$ (295)	$ 1,841,478