Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 61,333	$ 61,809	$ 164,148	$ 163,665
Available for sale securities:
Unrealized gains (losses) arising during the period	4,118	(9,768)	22,581	32,228
Income tax (expense) benefit related to unrealized gains (losses)	(1,594)	3,780	(8,745)	(12,472)
Reclassification adjustment for net realized (gains) losses in earnings	6	0	(27)	(858)
Income tax (benefit) expense related to realized (gains) losses	(3)	0	10	332
Other comprehensive income (loss), net of tax	2,527	(5,988)	13,819	19,230
Comprehensive income	$ 63,860	$ 55,821	$ 177,967	$ 182,895