Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended						6 Months Ended
	Jun. 30, 2019		Mar. 31, 2019		Jun. 30, 2018		Jun. 30, 2019	Jun. 30, 2018
Statement of Comprehensive Income [Abstract]
Net earnings	$ 128,125		$ 112,604		$ 115,735		$ 240,729	$ 234,011
Other comprehensive income (loss), net of tax:
Unrealized net holding gains (losses) on securities available-for-sale arising during the period	72,168		62,639		(14,325)		134,807	(76,994)
Income tax (expense) benefit related to unrealized holding gains (losses) arising during the period	(20,459)		(17,758)		4,102		(38,217)	22,033
Unrealized net holding gains (losses) on securities available-for-sale, net of tax	51,709		44,881		(10,223)		96,590	(54,961)
Reclassification adjustment for net (gains) losses included in net earnings	(22,192)	[1]	(2,161)	[1]	(253)	[1]	(24,353)	(6,564)
Income tax expense (benefit) related to reclassification adjustment	6,291		613		72		6,904	1,878
Reclassification adjustment for net (gains) losses included in net earnings, net of tax	(15,901)		(1,548)		(181)		(17,449)	(4,686)
Other comprehensive income (loss), net of tax	35,808		43,333		(10,404)		79,141	(59,647)
Comprehensive income	$ 163,933		$ 155,937		$ 105,331		$ 319,870	$ 174,364

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