Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2019		Jun. 30, 2019		Sep. 30, 2018		Sep. 30, 2019	Sep. 30, 2018
Statement of Comprehensive Income [Abstract]
Net earnings	$ 110,026		$ 128,125		$ 116,287		$ 350,755	$ 350,298
Other comprehensive income (loss), net of tax:
Unrealized net holding gains (losses) on securities available-for-sale arising during the period	32,759		72,168		(29,267)		167,566	(106,261)
Income tax (expense) benefit related to unrealized holding gains (losses) arising during the period	(9,287)		(20,459)		8,344		(47,504)	30,377
Unrealized net holding gains (losses) on securities available-for-sale, net of tax	23,472		51,709		(20,923)		120,062	(75,884)
Reclassification adjustment for net (gains) losses included in net earnings	(908)	[1]	(22,192)	[1]	(826)	[1]	(25,261)	(7,390)
Income tax expense (benefit) related to reclassification adjustment	257		6,291		235		7,161	2,113
Reclassification adjustment for net (gains) losses included in net earnings, net of tax	(651)		(15,901)		(591)		(18,100)	(5,277)
Other comprehensive income (loss), net of tax	22,821		35,808		(21,514)		101,962	(81,161)
Comprehensive income	$ 132,847		$ 163,933		$ 94,773		$ 452,717	$ 269,137

[1] Entire amounts are recognized in "Gain on sale of securities" on the Condensed Consolidated Statements of Earnings.