Condensed Consolidated Statement of Comprehensive Income - USD ($) $ in Thousands		3 Months Ended			9 Months Ended
		Sep. 30, 2016	Jun. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Statement of Comprehensive Income [Abstract]
Net earnings		$ 93,895	$ 82,168	$ 69,616	$ 266,519	$ 227,778
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax		(15,954)	56,514	14,466	83,653	616
Income tax (expense) benefit related to unrealized holding gains (losses) arising during the period		6,509	(22,965)	(5,873)	(34,111)	(364)
Unrealized net holding gains (losses) on securities available-for-sale, net of tax		(9,445)	33,549	8,593	49,542	252
Reclassification adjustment for net (gains) losses included in net earnings	[1]	(382)	(478)	(655)	(8,970)	(3,744)
Income tax expense (benefit) related to reclassification adjustment		156	194	266	3,673	1,571
Reclassification adjustment for net (gains) losses included in net earnings, net of tax		(226)	(284)	(389)	(5,297)	(2,173)
Other comprehensive income (loss), net of tax		(9,671)	33,265	8,204	44,245	(1,921)
Comprehensive income		$ 84,224	$ 115,433	$ 77,820	$ 310,764	$ 225,857

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