Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 42,842	$ 35,954	$ 118,056	$ 98,286
Other comprehensive income (loss), net of tax:
Net gains arising during the period	4,902	4,586	12,550	2,677
Less reclassification adjustment for net losses (gains) included in net income	6	(91)	(162)	(1,445)
Total	4,908	4,495	12,388	1,232
Non-credit impairment losses on available for sale securities
Net change in non-credit impairment losses on securities	(74)	252	168	(200)
Less reclassification adjustment for accretion of credit impairment losses included in net income	(50)	(267)	(336)	(371)
Total	(124)	(15)	(168)	(571)
Unrealized gains and losses on derivatives (cash flow hedges)
Net gains (losses) on derivatives arising during the period	1,735	(6,163)	(6,939)	(10,291)
Less reclassification adjustment for net losses included in net income	2,095	772	5,943	2,714
Total	3,830	(5,391)	(996)	(7,577)
Defined benefit pension plan
Amortization of net loss	42	119	128	359
Total other comprehensive income (loss)	8,656	(792)	11,352	(6,557)
Total comprehensive income	$ 51,498	$ 35,162	$ 129,408	$ 91,729