Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands		3 Months Ended			9 Months Ended
		Sep. 30, 2021	Jun. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Statement of Comprehensive Income [Abstract]
Net earnings		$ 139,996	$ 180,512	$ 45,503	$ 470,914	$ (1,354,404)
Other comprehensive income (loss), net of tax:
Unrealized net holding gains (losses) on securities available-for-sale arising during the period		(63,956)	54,076	19,745	(101,403)	119,708
Income tax (expense) benefit related to unrealized holding gains (losses) arising during the period		17,672	(14,941)	(5,510)	28,185	(33,399)
Unrealized net holding gains (losses) on securities available-for-sale, net of tax		(46,284)	39,135	14,235	(73,218)	86,309
Reclassification adjustment for net (gains) losses included in net earnings	[1]	(515)	0	(5,270)	(616)	(13,167)
Income tax expense (benefit) related to reclassification adjustment		142	0	1,471	170	3,674
Reclassification adjustment for net (gains) losses included in net earnings, net of tax		(373)	0	(3,799)	(446)	(9,493)
Other comprehensive income (loss), net of tax		(46,657)	39,135	10,436	(73,664)	76,816
Comprehensive income (loss)		$ 93,339	$ 219,647	$ 55,939	$ 397,250	$ (1,277,588)

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