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Portfolio Loans Not Covered by Loss Share ("Non-covered") - Summary of Non-covered Loans Individually Evaluated for Impairment by Category (Details) (USD $)
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3 Months Ended | 9 Months Ended | 12 Months Ended | 9 Months Ended | 12 Months Ended | 9 Months Ended | 12 Months Ended | 9 Months Ended | 12 Months Ended | 9 Months Ended | 12 Months Ended | 9 Months Ended | 12 Months Ended | 9 Months Ended | 12 Months Ended | |||
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Sep. 30, 2013
loan
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Sep. 30, 2013
loan
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Sep. 30, 2013
Non-Covered Loans
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Dec. 31, 2012
Non-Covered Loans
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Sep. 30, 2013
Non-Covered Loans
Commercial & Industrial
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Dec. 31, 2012
Non-Covered Loans
Commercial & Industrial
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Sep. 30, 2013
Non-Covered Loans
Commercial Real Estate Owner Occupied
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Dec. 31, 2012
Non-Covered Loans
Commercial Real Estate Owner Occupied
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Sep. 30, 2013
Non-Covered Loans
Commercial Real Estate Investor Owned
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Dec. 31, 2012
Non-Covered Loans
Commercial Real Estate Investor Owned
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Sep. 30, 2013
Non-Covered Loans
Construction and Land Development
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Dec. 31, 2012
Non-Covered Loans
Construction and Land Development
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Sep. 30, 2013
Non-Covered Loans
Residential Real Estate
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Dec. 31, 2012
Non-Covered Loans
Residential Real Estate
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Sep. 30, 2013
Non-Covered Loans
Consumer & Other
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Dec. 31, 2012
Non-Covered Loans
Consumer & Other
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Sep. 30, 2013
Unadvanced Commitment on Impaired Loan
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Dec. 31, 2012
Unadvanced Commitment on Impaired Loan
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| Financing Receivable, Impaired [Line Items] | ||||||||||||||||||
| Unpaid Contractual Principal Balance | $ 26,399,000 | $ 45,218,000 | $ 6,333,000 | $ 9,005,000 | $ 191,000 | $ 6,726,000 | $ 11,969,000 | $ 19,864,000 | $ 7,206,000 | $ 6,491,000 | $ 700,000 | $ 3,132,000 | $ 0 | $ 0 | ||||
| Recorded Investment With No Allowance | 11,334,000 | 5,645,000 | 1,441,000 | 96,000 | 195,000 | 2,178,000 | 4,960,000 | 185,000 | 4,278,000 | 1,560,000 | 460,000 | 1,626,000 | 0 | 0 | ||||
| Recorded Investment With Allowance | 13,416,000 | 33,082,000 | 4,642,000 | 8,838,000 | 0 | 3,594,000 | 6,158,000 | 16,577,000 | 2,389,000 | 3,135,000 | 227,000 | 938,000 | 0 | 0 | ||||
| Total Recorded Investment | 24,750,000 | 38,727,000 | 6,083,000 | 8,934,000 | 195,000 | 5,772,000 | 11,118,000 | 16,762,000 | 6,667,000 | 4,695,000 | 687,000 | 2,564,000 | 0 | 0 | ||||
| Related Allowance | 4,306,000 | 8,176,000 | 2,610,000 | 3,446,000 | 0 | 339,000 | 973,000 | 3,400,000 | 712,000 | 732,000 | 11,000 | 259,000 | 0 | 0 | ||||
| Average Recorded Investment | 29,632,000 | 39,491,000 | 7,379,000 | 6,379,000 | 2,381,000 | 7,985,000 | 12,346,000 | 10,500,000 | 5,165,000 | 10,259,000 | 2,361,000 | 4,368,000 | 0 | 0 | ||||
| Table Text Block Supplement [Abstract] | ||||||||||||||||||
| Number of loans over 90 days past due and still accruing | 0 | 0 | ||||||||||||||||
| Interest lost on impaired loans | 410,000 | 1,453,643 | ||||||||||||||||
| Impaired Financing Receivable, Interest Income, Cash Basis Method | 4,000 | 28,000 | ||||||||||||||||
| Impaired Financing Receivable, Interest Income, Accrual Method | 0 | |||||||||||||||||
| Loans and Leases Receivable, Impaired Loans, Commitment to Lend | 1,724,000 | 775,000 | ||||||||||||||||
| Estimated losses attributable to unadvanced commitments on impaired loans | $ 241,000 | $ 124,000 | ||||||||||||||||