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
	Mar. 31, 2013	Mar. 31, 2012	Sep. 30, 2012 loan	Mar. 31, 2013 Non-Covered Loans	Dec. 31, 2012 Non-Covered Loans	Mar. 31, 2013 Non-Covered Loans Commercial & Industrial	Dec. 31, 2012 Non-Covered Loans Commercial & Industrial	Mar. 31, 2013 Non-Covered Loans Real Estate Commercial - Investor Owned	Dec. 31, 2012 Non-Covered Loans Real Estate Commercial - Investor Owned	Mar. 31, 2013 Non-Covered Loans Real Estate Commercial - Owner Occupied	Dec. 31, 2012 Non-Covered Loans Real Estate Commercial - Owner Occupied	Mar. 31, 2013 Non-Covered Loans Real Estate Construction and Land Development	Dec. 31, 2012 Non-Covered Loans Real Estate Construction and Land Development	Mar. 31, 2013 Non-Covered Loans Real Estate Residential	Dec. 31, 2012 Non-Covered Loans Real Estate Residential	Mar. 31, 2013 Non-Covered Loans Consumer & Other	Dec. 31, 2012 Non-Covered Loans Consumer & Other	Mar. 31, 2013 Unadvanced Commitment on Impaired Loan
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number of loans over 90 days past due and still accruing			1
Interest lost on impaired loans	$ 765	$ 846
Cash collected and recognized as interest income	15	126
Interest income recognized on impaired loans continuing to accrue	29	160
Loans and Leases Receivable, Impaired Loans, Commitment to Lend																		127
Estimated losses attributable to unadvanced commitments on impaired loans																		20
Non-accrual				30,374	37,287	7,807	8,929	11,592	16,762	3,060	5,772	5,387	3,260	2,528	2,564	0	0
Restructured				5	1,440	5	5	0	0	0	0	0	1,435	0	0	0	0
Loans over 90 days past due and still accruing interest				1,843	0	0	0	1,843	0	0	0	0	0	0	0	0	0
Total Recorded Investment				$ 32,222	$ 38,727	$ 7,812	$ 8,934	$ 13,435	$ 16,762	$ 3,060	$ 5,772	$ 5,387	$ 4,695	$ 2,528	$ 2,564	$ 0	$ 0