Portfolio Loans Not Covered by Loss Share ("Non-covered") - Summary of Recorded Investment in Impaired Non-covered Loans by Category (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended
	Sep. 30, 2012 loan	Sep. 30, 2012 loan	Sep. 30, 2012 Non-Covered Loans	Dec. 31, 2011 Non-Covered Loans	Sep. 30, 2012 Non-Covered Loans Commercial & Industrial	Dec. 31, 2011 Non-Covered Loans Commercial & Industrial	Sep. 30, 2012 Non-Covered Loans Real Estate Commercial - Investor Owned	Dec. 31, 2011 Non-Covered Loans Real Estate Commercial - Investor Owned	Sep. 30, 2012 Non-Covered Loans Real Estate Commercial - Owner Occupied	Dec. 31, 2011 Non-Covered Loans Real Estate Commercial - Owner Occupied	Sep. 30, 2012 Non-Covered Loans Real Estate Construction and Land Development	Dec. 31, 2011 Non-Covered Loans Real Estate Construction and Land Development	Sep. 30, 2012 Non-Covered Loans Real Estate Residential	Dec. 31, 2011 Non-Covered Loans Real Estate Residential	Sep. 30, 2012 Non-Covered Loans Consumer & Other	Dec. 31, 2011 Non-Covered Loans Consumer & Other	Sep. 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	$ 708	$ 2,200
Cash collected and recognized as interest income	120	361
Interest income recognized on impaired loans continuing to accrue	174	412
Loans and Leases Receivable, Impaired Loans, Commitment to Lend																	543
Estimated losses attributable to unadvanced commitments on impaired loans																	98
Non-accrual			27,346	30,885	2,849	4,475	9,647	6,647	5,377	4,129	7,286	10,335	2,187	5,299	0	0
Restructured			4,712	9,982	0	1,159	0	4,480	207	443	2,809	3,677	1,696	223	0	0
Loans over 90 days past due and still accruing interest			0	755	0	0	0	0	0	0	0	755	0	0	0	0
Total Recorded Investment			$ 32,058	$ 41,622	$ 2,849	$ 5,634	$ 9,647	$ 11,127	$ 5,584	$ 4,572	$ 10,095	$ 14,767	$ 3,883	$ 5,522	$ 0	$ 0