Investment Securities (Narrative) (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2012 Organizaion Securities Banks	Sep. 30, 2011	Sep. 30, 2012 Securities Banks	Sep. 30, 2011	Dec. 31, 2011 Securities	Dec. 31, 2010
Investment [Line Items]
Other than Temporary Impairment Losses, Investments	$ 2,736,000	$ 13,334,000	$ 20,253,000	$ 21,597,000
Number of HTM investment securities in an unrealized loss position	95		95		72
Number of AFS investment securities in an unrealized loss position	296		296		525
Number of banks in CDO pools current following deferral period	63		63
Number of banks in CDO pools remaining in deferral	204		204
Number of NRSRO Ratings	1
Nontaxable interest income on securities	4,209,000	5,230,000	13,704,000	16,439,000
Carrying value of pledged securities	$ 1,440,990,000		$ 1,440,990,000			$ 1,500,000,000
Small Business Administration Loan-Backed Securities [Member] | Minimum [Member]
Investment [Line Items]
Investment term of maturity, in years			5
Small Business Administration Loan-Backed Securities [Member] | Maximum [Member]
Investment [Line Items]
Investment term of maturity, in years			25
Municipal Securities [Member] | Minimum [Member]
Investment [Line Items]
Investment term of maturity, in years			1
Municipal Securities [Member] | Maximum [Member]
Investment [Line Items]
Investment term of maturity, in years			25