Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ 31,991	$ 29,520	$ 62,332	$ 63,355
Other comprehensive income, net of tax:
Net (losses) gains arising during the period	(5,845)	7,123	(1,909)	14,339
Less reclassification adjustment for net losses (gains) included in net income	55	(4)	(1,354)	1
Total	(5,790)	7,119	(3,263)	14,340
Non-credit impairment losses on available for sale securities
Net change in non-credit impairment losses on securities	(31)	164	(452)	306
Less reclassification adjustment for accretion of credit impairment losses included in net income	(20)	(64)	(104)	(179)
Total	(51)	100	(556)	127
Unrealized gains and losses on derivatives (cash flow hedges)
Net gains (losses) on derivatives arising during the period	1,131	(4,862)	(4,128)	(8,524)
Less reclassification adjustment for net losses included in net income	991	973	1,942	1,938
Total	2,122	(3,889)	(2,186)	(6,586)
Defined benefit pension plan
Amortization of net loss	121	37	240	74
Total other comprehensive (loss) income	(3,598)	3,367	(5,765)	7,955
Total comprehensive income	$ 28,393	$ 32,887	$ 56,567	$ 71,310