Condensed Consolidated Statement of Comprehensive Income - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Statement of Comprehensive Income [Abstract]
Net earnings		$ 112,604	$ 115,041	$ 118,276
Other comprehensive income (loss), net of tax:
Unrealized net holding gains (losses) on securities available-for-sale arising during the period		62,639	53,702	(62,669)
Income tax (expense) benefit related to unrealized holding gains (losses) arising during the period		(17,758)	(15,362)	17,931
Unrealized net holding gains (losses) on securities available-for-sale, net of tax		44,881	38,340	(44,738)
Reclassification adjustment for net (gains) losses included in net earnings	[1]	(2,161)	(786)	(6,311)
Income tax expense (benefit) related to reclassification adjustment		613	225	1,806
Reclassification adjustment for net (gains) losses included in net earnings, net of tax		(1,548)	(561)	(4,505)
Other comprehensive income (loss), net of tax		43,333	37,779	(49,243)
Comprehensive income		$ 155,937	$ 152,820	$ 69,033

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