Condensed Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands		Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Treasury Stock	Shares Of Common Stock	Accumulated Other Comprehensive Income (Loss)
Beginning Period Balance at Dec. 31, 2017		$ 4,977,598	$ 1,305	$ 4,287,487	$ 723,471	$ (65,836)		$ 31,171
Shares outstanding, beginning balance (shares) at Dec. 31, 2017			128,782,878
Stockholders' Equity Disclosure [Rollforward]
Cumulative effect of change in accounting principle	[1]	0			(6,136)			6,136
Net earnings		118,276			118,276
Other comprehensive income - net unrealized gain on securities available-for-sale, net of tax		(49,243)						(49,243)
Restricted stock awarded and earned compensation, net of shares forfeited (shares)			96,034
Restricted stock awarded and earned stock compensation, net of shares forfeited		7,199	$ 1	7,198
Restricted stock surrendered (shares)			(55,186)				(2,285,855)
Restricted stock surrendered		(2,858)				(2,858)
Common stock repurchased under Stock Repurchase Program		(23)
Common stock repurchased under Stock Repurchase Program		(119,793)		(119,770)
Cash dividends paid		(63,689)		(63,689)
Ending Period Balance at Mar. 31, 2018		4,867,490	$ 1,283	4,111,226	835,611	(68,694)		(11,936)
Shares outstanding, ending balance (shares) at Mar. 31, 2018			126,537,871
Beginning Period Balance at Dec. 31, 2017		4,977,598	$ 1,305	4,287,487	723,471	(65,836)		31,171
Shares outstanding, beginning balance (shares) at Dec. 31, 2017			128,782,878
Stockholders' Equity Disclosure [Rollforward]
Net earnings		350,298
Ending Period Balance at Sep. 30, 2018		4,741,685	$ 1,251	3,789,893	1,067,633	(73,238)		(43,854)
Shares outstanding, ending balance (shares) at Sep. 30, 2018			123,283,450
Beginning Period Balance at Mar. 31, 2018		4,867,490	$ 1,283	4,111,226	835,611	(68,694)		(11,936)
Shares outstanding, beginning balance (shares) at Mar. 31, 2018			126,537,871
Stockholders' Equity Disclosure [Rollforward]
Net earnings		115,735			115,735
Other comprehensive income - net unrealized gain on securities available-for-sale, net of tax		(10,404)						(10,404)
Restricted stock awarded and earned compensation, net of shares forfeited (shares)			398,132
Restricted stock awarded and earned stock compensation, net of shares forfeited		7,546	$ 4	7,542
Restricted stock surrendered (shares)			(81,172)				(2,286,881)
Restricted stock surrendered		(4,332)				(4,332)
Common stock repurchased under Stock Repurchase Program		(23)
Common stock repurchased under Stock Repurchase Program		(122,024)		(122,001)
Cash dividends paid		(76,052)		(76,052)
Ending Period Balance at Jun. 30, 2018		$ 4,777,959	$ 1,264	3,920,715	951,346	(73,026)		(22,340)
Shares outstanding, ending balance (shares) at Jun. 30, 2018			124,567,950
Dividends declared per share (usd per share)		$ 0.50
Stockholders' Equity Disclosure [Rollforward]
Net earnings		$ 116,287			116,287
Other comprehensive income - net unrealized gain on securities available-for-sale, net of tax		(21,514)						(21,514)
Restricted stock awarded and earned compensation, net of shares forfeited (shares)			(3,803)
Restricted stock awarded and earned stock compensation, net of shares forfeited		8,137		8,137
Restricted stock surrendered (shares)			(4,199)				(1,276,498)
Restricted stock surrendered		(212)				(212)
Common stock repurchased under Stock Repurchase Program		(13)
Common stock repurchased under Stock Repurchase Program		(64,577)		(64,564)
Cash dividends paid		(74,395)		(74,395)
Ending Period Balance at Sep. 30, 2018		4,741,685	$ 1,251	3,789,893	1,067,633	(73,238)		(43,854)
Shares outstanding, ending balance (shares) at Sep. 30, 2018			123,283,450
Beginning Period Balance at Dec. 31, 2018		4,825,588	$ 1,251	3,722,723	1,182,674	(74,985)		(6,075)
Shares outstanding, beginning balance (shares) at Dec. 31, 2018			123,189,833
Stockholders' Equity Disclosure [Rollforward]
Net earnings		112,604			112,604
Other comprehensive income - net unrealized gain on securities available-for-sale, net of tax		43,333						43,333
Restricted stock awarded and earned compensation, net of shares forfeited (shares)			195,536
Restricted stock awarded and earned stock compensation, net of shares forfeited		5,808	$ 2	5,806
Restricted stock surrendered (shares)			(113,544)				(3,070,676)
Restricted stock surrendered		(4,522)				(4,522)
Common stock repurchased under Stock Repurchase Program		(31)
Common stock repurchased under Stock Repurchase Program		(119,587)		(119,556)
Cash dividends paid		(73,180)		(73,180)
Ending Period Balance at Mar. 31, 2019		4,790,982	$ 1,222	3,535,793	1,296,216	(79,507)		37,258
Shares outstanding, ending balance (shares) at Mar. 31, 2019			120,201,149
Beginning Period Balance at Dec. 31, 2018		4,825,588	$ 1,251	3,722,723	1,182,674	(74,985)		(6,075)
Shares outstanding, beginning balance (shares) at Dec. 31, 2018			123,189,833
Stockholders' Equity Disclosure [Rollforward]
Net earnings		350,755
Ending Period Balance at Sep. 30, 2019		4,920,108	$ 1,219	3,371,032	1,534,367	(82,397)		95,887
Shares outstanding, ending balance (shares) at Sep. 30, 2019			119,831,192
Beginning Period Balance at Mar. 31, 2019		4,790,982	$ 1,222	3,535,793	1,296,216	(79,507)		37,258
Shares outstanding, beginning balance (shares) at Mar. 31, 2019			120,201,149
Stockholders' Equity Disclosure [Rollforward]
Net earnings		128,125			128,125
Other comprehensive income - net unrealized gain on securities available-for-sale, net of tax		35,808						35,808
Restricted stock awarded and earned compensation, net of shares forfeited (shares)			619,653
Restricted stock awarded and earned stock compensation, net of shares forfeited		6,721	$ 6	6,715
Restricted stock surrendered (shares)			(74,429)				(917,269)
Restricted stock surrendered		(2,788)				(2,788)
Common stock repurchased under Stock Repurchase Program		(9)
Common stock repurchased under Stock Repurchase Program		(34,929)		(34,920)		0
Cash dividends paid		(71,909)		(71,909)
Ending Period Balance at Jun. 30, 2019		$ 4,852,010	$ 1,219	3,435,679	1,424,341	(82,295)		73,066
Shares outstanding, ending balance (shares) at Jun. 30, 2019			119,829,104
Dividends declared per share (usd per share)		$ 0.60
Stockholders' Equity Disclosure [Rollforward]
Net earnings		$ 110,026			110,026
Other comprehensive income - net unrealized gain on securities available-for-sale, net of tax		22,821						22,821
Restricted stock awarded and earned compensation, net of shares forfeited (shares)			5,040
Restricted stock awarded and earned stock compensation, net of shares forfeited		7,305	$ 0	7,305
Restricted stock surrendered (shares)			(2,952)
Restricted stock surrendered		(102)				(102)
Cash dividends paid		(71,952)		(71,952)
Ending Period Balance at Sep. 30, 2019		$ 4,920,108	$ 1,219	$ 3,371,032	$ 1,534,367	$ (82,397)		$ 95,887
Shares outstanding, ending balance (shares) at Sep. 30, 2019			119,831,192

[1] Impact due to adoption on January 1, 2019 of ASU 2016-02, "Leases (Topic 842)," and the related amendments.