Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands		3 Months Ended			6 Months Ended
		Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Statement of Comprehensive Income [Abstract]
Net earnings		$ 180,512	$ 150,406	$ 33,204	$ 330,918	$ (1,399,907)
Other comprehensive income (loss), net of tax:
Unrealized net holding gains (losses) on securities available-for-sale arising during the period		54,076	(91,523)	82,780	(37,447)	99,963
Income tax (expense) benefit related to unrealized holding gains (losses) arising during the period		(14,941)	25,454	(23,095)	10,513	(27,889)
Unrealized net holding gains (losses) on securities available-for-sale, net of tax		39,135	(66,069)	59,685	(26,934)	72,074
Reclassification adjustment for net (gains) losses included in net earnings	[1]	0	(101)	(7,715)	(101)	(7,897)
Income tax expense (benefit) related to reclassification adjustment		0	28	2,152	28	2,203
Reclassification adjustment for net (gains) losses included in net earnings, net of tax		0	(73)	(5,563)	(73)	(5,694)
Other comprehensive income (loss), net of tax		39,135	(66,142)	54,122	(27,007)	66,380
Comprehensive income (loss)		$ 219,647	$ 84,264	$ 87,326	$ 303,911	$ (1,333,527)

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