Consolidated Statement of Comprehensive Income - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015
Statement of Comprehensive Income [Abstract]
Net earnings		$ 90,456	$ 71,841	$ 73,079
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Unrealized holding (losses) gains on securities available-for-sale		43,093	5,874	7,363
Income tax benefit (expense) related to unrealized holding (losses) gains arising during the period		(17,655)	(2,505)	(3,105)
Unrealized holding losses (gains) on securities available-for-sale, net of tax		25,438	3,369	4,258
Reclassification adjustment for losses (gains) included in net earnings	[1]	(8,110)	0	(3,275)
Income tax (benefit) expense related to reclassification adjustment		3,323	0	1,381
Reclassification adjustment for losses (gains) included in net earnings, net of tax		(4,787)	0	(1,894)
Other comprehensive (loss) income, net of tax		20,651	3,369	2,364
Comprehensive income		$ 111,107	$ 75,210	$ 75,443

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