Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands		3 Months Ended			9 Months Ended
		Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement of Comprehensive Income [Abstract]
Net earnings		$ 45,503	$ 33,204	$ 110,026	$ (1,354,404)	$ 350,755
Other comprehensive income, net of tax:
Unrealized net holding gains (losses) on securities available-for-sale arising during the period		19,745	82,780	32,759	119,708	167,566
Income tax (expense) benefit related to unrealized holding gains (losses) arising during the period		(5,510)	(23,095)	(9,287)	(33,399)	(47,504)
Unrealized net holding gains (losses) on securities available-for-sale, net of tax		14,235	59,685	23,472	86,309	120,062
Reclassification adjustment for net (gains) losses included in net earnings	[1]	(5,270)	(7,715)	(908)	(13,167)	(25,261)
Income tax expense (benefit) related to reclassification adjustment		1,471	2,152	257	3,674	7,161
Reclassification adjustment for net (gains) losses included in net earnings, net of tax		(3,799)	(5,563)	(651)	(9,493)	(18,100)
Other comprehensive income, net of tax		10,436	54,122	22,821	76,816	101,962
Comprehensive income (loss)		$ 55,939	$ 87,326	$ 132,847	$ (1,277,588)	$ 452,717

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