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Loans and Loans Held for Sale - Additional Information (Detail) | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2016 USD ($) contract | Jun. 30, 2015 USD ($) | Jun. 30, 2016 USD ($) contract | Jun. 30, 2015 USD ($) | Dec. 31, 2015 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Loans, net of unearned income | $ 4,500,000 |  | $ 4,500,000 |  | $ 3,200,000
Loans, net of discount related to purchase accounting adjustments | 9,000,000 |  | 9,000,000 |  | $ 10,900,000
Maximum concentration of commercial real estate and commercial construction portfolio in loans (in excess of) |  |  |  |  | 7.00%
Decrease in loans held for sale during the period |  |  | 23,300,000 |  |
Gain on sale of credit card portfolio | 0 | $ 0 | 2,066,000 | $ 0 |
Commitment to lend additional funds on troubled debt restructuring | $ 700,000.0 |  | $ 700,000.0 |  |
Minimum period of loan payment defaults following restructure for TDRs to be in default |  |  | 90 days |  |
Commercial and Industrial |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Number of loans modified not considered to be troubled debt restructuring | contract | 1 |  | 3 |  |
Loans modified not considered to be troubled debt restructuring | $ 6,500,000 |  | $ 8,700,000 |  |
Installment and Other Consumer |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Decrease in loans held for sale during the period |  |  | 22,900,000 |  |
Gain on sale of credit card portfolio |  |  | $ 2,100,000 |  |
Commercial Real Estate and Commercial Construction |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Out of market exposure of combined portfolio (percent) | 5.30% |  | 5.30% |  | 5.80%
Percentage of total loans out-of-state excluding contiguous states | 2.70% |  | 2.70% |  | 3.00%
Commercial Real Estate |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Number of loans modified not considered to be troubled debt restructuring | contract | 1 |  | 1 |  |
Loans modified not considered to be troubled debt restructuring | $ 500,000 |  | $ 500,000 |  |
Commercial |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Percentage of commercial loans in total portfolio loans | 77.00% |  | 77.00% |  | 76.00%
Commercial Loans | $ 4,172,654,000 |  | $ 4,172,654,000 |  | $ 3,836,877,000
Concentration Risk, Product |  |  | 0 | 0 |
Maximum concentration of commercial real estate and commercial construction portfolio in loans (in excess of) | 7.00% |  | 7.00% |  | 7.00%
Commercial | Commercial and Industrial |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Commercial Loans | $ 1,385,746,000 |  | $ 1,385,746,000 |  | $ 1,256,830,000
Commercial | Commercial Real Estate and Commercial Construction |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Commercial Loans | $ 2,800,000,000 |  | $ 2,800,000,000 |  |
Combined percentage of commercial real estate and commercial construction in total commercial loans | 67.00% |  | 67.00% |  | 67.00%
Combined percentage of commercial real estate and commercial construction in total portfolio loans | 52.00% |  | 52.00% |  | 51.00%
Commercial | Commercial Real Estate |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Commercial Loans | $ 2,388,786,000 |  | $ 2,388,786,000 |  | $ 2,166,603,000

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