Condensed Consolidated Statements of Changes in Stockholders' Equity - USD ($)		Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Treasury Stock	Shares Of Common Stock	Accumulated Other Comprehensive Income (Loss)
Dividends declared per share (usd per share)		$ 0.50
Beginning Period Balance at Dec. 31, 2017		$ 4,977,598,000	$ 1,305,000	$ 4,287,487,000	$ 723,471,000	$ (65,836,000)		$ 31,171,000
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			(6,136,000)			6,136,000
Net earnings		118,276,000			118,276,000
Other comprehensive income - net unrealized gain on securities available-for-sale, net of tax		(49,243,000)						(49,243,000)
Restricted stock awarded and earned compensation, net of shares forfeited (shares)			96,034
Restricted stock awarded and earned stock compensation, net of shares forfeited		7,199,000	$ 1,000	7,198,000
Restricted stock surrendered (shares)			(55,186)				(2,285,855)
Restricted stock surrendered		(2,858,000)				(2,858,000)
Common stock repurchased under Stock Repurchase Program		(23,000)
Common stock repurchased under Stock Repurchase Program		(119,793,000)		(119,770,000)
Cash dividends paid		(63,689,000)		(63,689,000)
Ending Period Balance at Mar. 31, 2018		$ 4,867,490,000	$ 1,283,000	4,111,226,000	835,611,000	(68,694,000)		(11,936,000)
Shares outstanding, ending balance (shares) at Mar. 31, 2018			126,537,871
Dividends declared per share (usd per share)		$ 0.60
Beginning Period Balance at Dec. 31, 2018		$ 4,825,588,000	$ 1,251,000	3,722,723,000	1,182,674,000	(74,985,000)		(6,075,000)
Shares outstanding, beginning balance (shares) at Dec. 31, 2018			123,189,833
Stockholders' Equity Disclosure [Rollforward]
Cumulative effect of change in accounting principle	[1]	938,000			938,000
Net earnings		112,604,000			112,604,000
Other comprehensive income - net unrealized gain on securities available-for-sale, net of tax		43,333,000						43,333,000
Restricted stock awarded and earned compensation, net of shares forfeited (shares)			195,536
Restricted stock awarded and earned stock compensation, net of shares forfeited		5,808,000	$ 2,000	5,806,000
Restricted stock surrendered (shares)			(113,544)				(3,070,676)
Restricted stock surrendered		(4,522,000)				(4,522,000)
Common stock repurchased under Stock Repurchase Program		(31,000)
Common stock repurchased under Stock Repurchase Program		(119,587,000)		(119,556,000)
Cash dividends paid		(73,180,000)		(73,180,000)
Ending Period Balance at Mar. 31, 2019		$ 4,790,982,000	$ 1,222,000	$ 3,535,793,000	$ 1,296,216,000	$ (79,507,000)		$ 37,258,000
Shares outstanding, ending balance (shares) at Mar. 31, 2019			120,201,149

[1] Three Months Ended March 31, 2018 Common Stock Accumulated Additional Other Par Paid-in Retained Treasury Comprehensive Shares Value Capital Earnings Stock Income (Loss) Total (Unaudited) (Dollars in thousands)Balance, December 31, 2017128,782,878 $1,305 $4,287,487 $723,471 $(65,836) $31,171 $4,977,598Cumulative effect of changes in accounting principles (2)— — — (6,136) — 6,136 —Net earnings— — — 118,276 — — 118,276Other comprehensive loss - net unrealized loss on securities available-for-sale, net of tax— — — — — (49,243) (49,243)Restricted stock awarded and earned stock compensation, net of shares forfeited96,034 1 7,198 — — — 7,199Restricted stock surrendered(55,186) — — — (2,858) — (2,858)Common stock repurchased under Stock Repurchase Program(2,285,855) (23) (119,770) — — — (119,793)Cash dividends paid: Common stock, $0.50/share— — (63,689) — — — (63,689)Balance, March 31, 2018126,537,871 $1,283 $4,111,226 $835,611 $(68,694) $(11,936) $4,867,490