Portfolio Loans Not Covered by Loss Share ("Non-covered") - Summary of Recorded Investment in Impaired Non-covered Loans by Category (Details) (USD $)	3 Months Ended	6 Months Ended
	Jun. 30, 2012 loan	Jun. 30, 2012 loan	Jun. 30, 2012 Non-Covered Loans	Dec. 31, 2011 Non-Covered Loans	Jun. 30, 2012 Non-Covered Loans Commercial & Industrial	Dec. 31, 2011 Non-Covered Loans Commercial & Industrial	Jun. 30, 2012 Non-Covered Loans Real Estate Commercial - Investor Owned	Dec. 31, 2011 Non-Covered Loans Real Estate Commercial - Investor Owned	Jun. 30, 2012 Non-Covered Loans Real Estate Commercial - Owner Occupied	Dec. 31, 2011 Non-Covered Loans Real Estate Commercial - Owner Occupied	Jun. 30, 2012 Non-Covered Loans Real Estate Construction and Land Development	Dec. 31, 2011 Non-Covered Loans Real Estate Construction and Land Development	Jun. 30, 2012 Non-Covered Loans Real Estate Residential	Dec. 31, 2011 Non-Covered Loans Real Estate Residential	Jun. 30, 2012 Non-Covered Loans Consumer & Other	Dec. 31, 2011 Non-Covered Loans Consumer & Other	Jun. 30, 2012 Unadvanced Commitment on Impaired Loan
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number of loans over 90 days past due and still accruing	0	0
Interest lost on impaired loans	$ 676,000	$ 1,500,000
Cash collected and recognized as interest income	115,000	241,000
Interest income recognized on impaired loans continuing to accrue	79,000	238,000
Loans and Leases Receivable, Impaired Loans, Commitment to Lend																	1,100,000
Estimated losses attributable to unadvanced commitments on impaired loans																	212,000
Non-accrual			30,143,000	30,885,000	4,008,000	4,475,000	5,143,000	6,647,000	10,130,000	4,129,000	8,015,000	10,335,000	2,847,000	5,299,000	0	0
Restructured			10,412,000	9,982,000	659,000	1,159,000	4,794,000	4,480,000	0	443,000	3,263,000	3,677,000	1,696,000	223,000	0	0
Loans over 90 days past due and still accruing interest			0	755,000	0	0	0	0	0	0	0	755,000	0	0	0	0
Total Recorded Investment			$ 40,555,000	$ 41,622,000	$ 4,667,000	$ 5,634,000	$ 9,937,000	$ 11,127,000	$ 10,130,000	$ 4,572,000	$ 11,278,000	$ 14,767,000	$ 4,543,000	$ 5,522,000	$ 0	$ 0