Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ 35,954	$ 27,682	$ 98,286	$ 91,037
Other comprehensive (loss) income, net of tax:
Net gains (losses) arising during the period	4,586	(488)	2,677	13,851
Less reclassification adjustment for net gains included in net income	(91)	(60)	(1,445)	(59)
Total	4,495	(548)	1,232	13,792
Non-credit impairment losses on available for sale securities
Net change in non-credit impairment losses on securities	252	313	(200)	619
Less reclassification adjustment for accretion of credit impairment losses included in net income	(267)	(115)	(371)	(294)
Total	(15)	198	(571)	325
Unrealized gains and losses on derivatives (cash flow hedges)
Net (losses) gains on derivatives arising during the period	(6,163)	1,251	(10,291)	(7,273)
Less reclassification adjustment for net losses included in net income	772	973	2,714	2,911
Total	(5,391)	2,224	(7,577)	(4,362)
Defined benefit pension plan
Amortization of net loss	119	36	359	110
Total other comprehensive (loss) income	(792)	1,910	(6,557)	9,865
Total comprehensive income	$ 35,162	$ 29,592	$ 91,729	$ 100,902