Consolidated Statements Of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Consolidated Statements Of Comprehensive Income [Abstract]
Net income	$ 34,531	$ 36,585
Other comprehensive income, net of tax:
Net gains arising during the period	4,226	1,813
Less reclassification adjustment for losses (gains) included in net income	95	(1,679)
Total	4,321	134
Non-credit impairment losses on available for sale and held to maturity securities
Net change in non-credit impairment losses on securities	7,070	102
Less reclassification adjustment for credit impairment losses included in net income	(190)	418
Total	6,880	520
Unrealized gains and losses on derivatives (cash flow hedges)
Net gains on derivatives arising during the period	899	832
Less reclassification adjustment for losses included in net income	808	335
Total	1,707	1,167
Pension benefit adjustment	441	292
Total other comprehensive income	13,349	2,113
Total comprehensive income	$ 47,880	$ 38,698