Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Statement of Comprehensive Income [Abstract]
Net income	$ 27,682	$ 27,121	$ 91,037	$ 92,353
Other comprehensive income, net of tax:
Net (losses) gains arising during the period	(488)	1,929	13,851	(15,111)
Less reclassification adjustment for net gains included in net income	(60)	(6)	(59)	(2,330)
Total	(548)	1,923	13,792	(17,441)
Non-credit impairment losses on available for sale securities
Net change in non-credit impairment losses on securities	313	226	619	6,977
Less reclassification adjustment for accretion of credit impairment losses included in net income	(115)	(110)	(294)	(219)
Total	198	116	325	6,758
Unrealized gains and losses on derivatives (cash flow hedges)
Net gains (losses) on derivatives arising during the period	1,251	(2,866)	(7,273)	(907)
Less reclassification adjustment for net losses included in net income	973	950	2,911	3,036
Total	2,224	(1,916)	(4,362)	2,129
Defined benefit pension plan
Net gains arising during the period	0	0	0	18,769
Amortization of prior service cost	0	134	0	395
Amortization of net loss	36	209	110	1,145
Recognition of loss due to curtailment	0	0	0	468
Total	36	343	110	20,777
Total other comprehensive income	1,910	466	9,865	12,223
Total comprehensive income	$ 29,592	$ 27,587	$ 100,902	$ 104,576