Consolidated Statement of Comprehensive Income - USD ($) $ in Thousands		3 Months Ended			6 Months Ended
		Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Statement of Comprehensive Income [Abstract]
Net earnings		$ 82,168	$ 90,456	$ 85,083	$ 172,624	$ 158,162
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax		56,514	43,093	(21,213)	99,607	(13,850)
Income tax (expense) benefit related to unrealized holding gains (losses) arising during the period		(22,965)	(17,655)	8,614	(40,620)	5,509
Unrealized net holding gains (losses) on securities available-for-sale, net of tax		33,549	25,438	(12,599)	58,987	(8,341)
Reclassification adjustment for net (gains) losses included in net earnings	[1]	(478)	(8,110)	186	(8,588)	(3,089)
Income tax expense (benefit) related to reclassification adjustment		194	3,323	(76)	3,517	1,305
Reclassification adjustment for net (gains) losses included in net earnings, net of tax		(284)	(4,787)	110	(5,071)	(1,784)
Other comprehensive income (loss), net of tax		33,265	20,651	(12,489)	53,916	(10,125)
Comprehensive income		$ 115,433	$ 111,107	$ 72,594	$ 226,540	$ 148,037

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