Condensed Consolidated Statement of Shareholders' Equity - 6 months ended Jun. 30, 2018 - USD ($) $ in Thousands		Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Treasury Stock	Shares Of Common Stock	Accumulated Other Comprehensive Income (Loss)
Balance, December 31, 2017 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		0	(6,136)			6,136
Net earnings		234,011			234,011
Other comprehensive income - net unrealized gain on securities available-for-sale, net of tax		(59,647)						(59,647)
Restricted stock awarded and earned compensation, net of shares forfeited (shares)			494,166
Restricted stock awarded and earned stock compensation, net of shares forfeited		14,745	$ 5	14,740
Restricted stock surrendered (shares)			(136,358)				(4,572,736)
Restricted stock surrendered		(7,190)				(7,190)
Common stock repurchased under Stock Repurchase Program		46
Common stock repurchased under Stock Repurchase Program		241,817		241,771		0
Cash dividends paid		(139,741)		(139,741)
Balance, June 30, 2018 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

[1] Impact due to adoption on January 1, 2018 of ASU 2016-01, "Financial Instruments - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities" and ASU 2018-02, "Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income."