Condensed Consolidated Statement of Comprehensive Income - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016
Statement of Comprehensive Income [Abstract]
Net earnings		$ 78,668	$ 85,647	$ 90,456
Other comprehensive income (loss), net of tax:
Unrealized net holding gains (losses) on securities available-for-sale arising during the period		11,184	(111,045)	43,093
Income tax (expense) benefit related to unrealized holding gains (losses) arising during the period		(4,507)	45,259	(17,655)
Unrealized net holding gains (losses) on securities available-for-sale, net of tax		6,677	(65,786)	25,438
Reclassification adjustment for net (gains) losses included in net earnings	[1]	99	(515)	(8,110)
Income tax expense (benefit) related to reclassification adjustment		(40)	210	3,323
Reclassification adjustment for net (gains) losses included in net earnings, net of tax		59	(305)	(4,787)
Other comprehensive income (loss), net of tax		6,736	(66,091)	20,651
Comprehensive income		$ 85,404	$ 19,556	$ 111,107

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