Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 56,812	$ 54,287	$ 102,815	$ 101,856
Available for sale securities:
Unrealized gains arising during the period	14,321	10,346	18,463	41,997
Income tax expense related to unrealized gains	(5,547)	(4,004)	(7,151)	(16,253)
Reclassification adjustment for net realized gains in earnings	(35)	(162)	(33)	(858)
Income tax expense related to realized gains	14	63	13	332
Other comprehensive income, net of tax	8,753	6,243	11,292	25,218
Comprehensive income	$ 65,565	$ 60,530	$ 114,107	$ 127,074