Loans and Allowance for Credit Losses Narrative (Details) (USD $)	1 Months Ended	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Financing Receivable, Allowance for Credit Losses [Line Items]
Provision for loan losses gross		$ 62,000	$ 1,100,000	$ 127,000	$ 723,000
Provision for credit losses		25,500,000	36,000,000	53,500,000	74,000,000
Percentage of unallocated allowance	9.00%	9.00%	13.00%	9.00%	13.00%
Minimum balance of loans evaluated individually for impairment				1,000,000
Impaired loans with principal balances approximately in percentage				78.00%	85.00%
Impaired loans balances, real estate as collateral	1,000,000	1,000,000		1,000,000
Loan to value ratio in the Corporation's policy	80.00%	80.00%		80.00%
Recorded investment, with no related allowance	106,340,000	106,340,000		106,340,000		109,938,000
TDR additional commitments to lend	1,500,000	1,500,000		1,500,000		1,700,000
Recorded Investment, Loans Sold	(44,110,000)
Charge-offs Upon Sale, Loan Sold	$ (21,180,000)
Delinquent [Member] | Minimum [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Days past due				31
Delinquent [Member] | Maximum [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Days past due				89
Non-performing [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Days past due				90