Consolidated Statements Of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Consolidated Statements Of Comprehensive Income [Abstract]
Net income	$ 133,653	$ 131,170	$ 116,061
Other comprehensive (loss) income, net of tax:
Net gains arising during the period	1,513	12,637	47,351
Less reclassification adjustment for gains included in net income	(19,674)	(7,330)	(5,003)
Total	(18,161)	5,307	42,348
Non-credit impairment losses on available for sale and held to maturity securities
Net change in non-credit impairment losses on securities	(26,656)	3,328	(2,774)
Less reclassification adjustment for credit impairment losses included in net income	11,633	2,741	3,767
Total	(15,023)	6,069	993
Unrealized gains and losses on derivatives (cash flow hedges)
Net (losses) gains on derivatives arising during the period	(14,157)	866	2,017
Less reclassification adjustment for losses included in net income	1,780	1,142	267
Total	(12,377)	2,008	2,284
Pension benefit adjustment	(11,161)	713	4,095
Total other comprehensive (loss) income	(56,722)	14,097	49,720
Total comprehensive income	$ 76,931	$ 145,267	$ 165,781