Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Statement of Comprehensive Income [Abstract]
Net income	$ 33,835	$ 31,310
Other comprehensive income, net of tax:
Net gains (losses) arising during the period	7,216	(687)
Less reclassification adjustment for net (gains) losses included in net income	5	(2,299)
Total	7,221	(2,986)
Non-credit impairment losses on available for sale securities
Net change in non-credit impairment losses on securities	142	4,743
Less reclassification adjustment for credit impairment losses included in net income	(115)	(66)
Total	27	4,677
Unrealized gains and losses on derivatives (cash flow hedges)
Net losses on derivatives arising during the period	(3,662)	(77)
Less reclassification adjustment for net losses included in net income	965	1,091
Total	(2,697)	1,014
Defined benefit pension plan
Amortization of prior service cost	0	118
Amortization of net loss	37	460
Total	37	578
Total other comprehensive income	4,588	3,283
Total comprehensive income	$ 38,423	$ 34,593