Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Statement of Comprehensive Income [Abstract]
Net income	$ 29,520	$ 33,922	$ 63,355	$ 65,232
Other comprehensive income, net of tax:
Net gains (losses) arising during the period	7,123	(16,353)	14,339	(17,040)
Less reclassification adjustment for net (gains) losses included in net income	(4)	(25)	1	(2,324)
Total	7,119	(16,378)	14,340	(19,364)
Non-credit impairment losses on available for sale securities
Net change in non-credit impairment losses on securities	164	2,008	306	6,751
Less reclassification adjustment for accretion of credit impairment losses included in net income	(64)	(43)	(179)	(109)
Total	100	1,965	127	6,642
Unrealized gains and losses on derivatives (cash flow hedges)
Net (losses) gains on derivatives arising during the period	(4,862)	2,036	(8,524)	1,959
Less reclassification adjustment for net losses included in net income	973	995	1,938	2,086
Total	(3,889)	3,031	(6,586)	4,045
Defined benefit pension plan
Net gains arising during the period	0	18,784	0	18,769
Amortization of prior service cost	0	133	0	261
Amortization of net loss	37	471	74	936
Recognition of loss due to curtailment	0	468	0	468
Total	37	19,856	74	20,434
Total other comprehensive income	3,367	8,474	7,955	11,757
Total comprehensive income	$ 32,887	$ 42,396	$ 71,310	$ 76,989