Condensed Consolidated Statement of Comprehensive Income - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Net earnings		$ 118,276	$ 84,037	$ 78,668
Other comprehensive (loss) income, net of tax:
Unrealized net holding gains (losses) on securities available-for-sale arising during the period		(62,669)	(7,146)	11,184
Income tax (expense) benefit related to unrealized holding gains (losses) arising during the period		17,931	2,574	(4,507)
Unrealized net holding gains (losses) on securities available-for-sale, net of tax		(44,738)	(4,572)	6,677
Reclassification adjustment for net (gains) losses included in net earnings	[1]	(6,311)	3,329	99
Income tax expense (benefit) related to reclassification adjustment		1,806	(1,199)	(40)
Reclassification adjustment for net (gains) losses included in net earnings, net of tax		(4,505)	2,130	59
Other comprehensive (loss) income, net of tax		(49,243)	(2,442)	6,736
Comprehensive income		$ 69,033	$ 81,595	$ 85,404

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