Consolidated Statements Of Shareholders' Equity - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Common Shares	Additional Paid-in Capital	Additional Paid-in Capital Cumulative Effect, Period of Adoption, Adjustment	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Retained Earnings Cumulative Effect, Period of Adoption, Adjustment
Shareholders' Equity, shares at Dec. 31, 2017			286,752,000
Shareholders' Equity at Dec. 31, 2017	$ 4,154,026	$ 22,411	$ 2,868	$ 3,171,542	$ 0	$ (445)	$ 980,061
Stock option exercises, shares			605,000
Stock option exercises	6,555		$ 6	6,549
Share issuances, net of cancellations, shares			1,210,000
Share issuances	3,487		$ 12	3,475
Dividends declared	(108,489)						(108,489)
Share repurchases, shares			(11,457,000)
Share repurchases	(294,566)		$ (115)				(294,451)
Cash paid for shares withheld for taxes	7,910			284			7,626
Share-based compensation	20,145			20,145
Net income	1,022,023						1,022,023
Other comprehensive income	100					100
Shareholders' Equity, shares at Dec. 31, 2018			277,110,000
Shareholders' Equity at Dec. 31, 2018	4,817,782		$ 2,771	3,201,427		(345)	1,613,929
Stock option exercises, shares			547,000
Stock option exercises	6,399		$ 5	6,394
Share issuances, net of cancellations, shares			1,013,000
Share issuances	5,800		$ 10	5,790
Dividends declared	(124,356)						(124,356)
Share repurchases, shares			(8,435,000)
Share repurchases	(274,333)		$ (84)				(274,249)
Cash paid for shares withheld for taxes	11,450						11,450
Share-based compensation	21,538			21,538
Net income	1,016,700						1,016,700
Other comprehensive income	$ 100					100
Shareholders' Equity, shares at Dec. 31, 2019	270,235,297		270,235,000
Shareholders' Equity at Dec. 31, 2019	$ 5,458,180	$ (735)	$ 2,702	3,235,149		(245)	2,220,574	$ (735)
Stock option exercises, shares			15,000
Stock option exercises	111		$ 1	110
Share issuances, net of cancellations, shares			756,000
Share issuances	4,096		$ 8	4,088
Dividends declared	(135,138)						(135,138)
Share repurchases, shares			(4,542,000)
Share repurchases	(170,676)		$ (46)				(170,630)
Cash paid for shares withheld for taxes	14,853						14,853
Share-based compensation	22,065			22,065
Net income	1,406,839						1,406,839
Other comprehensive income	$ 100					100
Shareholders' Equity, shares at Dec. 31, 2020	266,464,063		266,464,000
Shareholders' Equity at Dec. 31, 2020	$ 6,569,989		$ 2,665	$ 3,261,412		$ (145)	$ 3,306,057