Non-Covered Loans and Allowance for Non-Covered Loan Losses (Details 4) (USD $)	3 Months Ended
	Mar. 31, 2015 item	Mar. 31, 2014 item	Dec. 31, 2014
AB Note | Minimum | Bank
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Number of loans into which a single loan is reconfigured	2
Noncovered
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total Modifications	75,000	$ 745,000
Number of TDRs granted in preceding twelve months for which payment was at least 30 days past due	0	0
Noncovered | Bank
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Unadvanced commitments to borrowers	600,000		500,000
Noncovered | Payment Term Extension
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total Modifications	75,000	745,000
Noncovered | Secured by commercial properties
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total Modifications		345,000
Noncovered | Secured by commercial properties | Payment Term Extension
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total Modifications		345,000
Noncovered | Secured by residential properties
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total Modifications		258,000
Noncovered | Secured by residential properties | Payment Term Extension
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total Modifications		258,000
Noncovered | Commercial construction loans and land development
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total Modifications	75,000	142,000
Noncovered | Commercial construction loans and land development | Payment Term Extension
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total Modifications	75,000	$ 142,000