Loans and Allowance for Credit Losses Narrative (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Financing Receivable, Allowance for Credit Losses [Line Items]
Provision for loan losses gross	$ 50,000	$ 65,000
Provision for credit losses	15,000,000	28,000,000
Percentage of unallocated allowance	10.00%	8.00%
Recorded Investment, Loans Sold	(9,880,000)
Charge-offs Upon Sale, Loan Sold	(5,240,000)
Minimum balance of loans evaluated individually for impairment	1,000,000
Impaired loans with principal balances approximately in percentage	73.00%	82.00%
Impaired loans balances, real estate as collateral	1,000,000
Loan to value ratio in the Corporation's policy	70.00%
Recorded investment, with no related allowance	90,433,000		94,451,000
TDR additional commitments to lend	$ 7,300,000		$ 7,400,000
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