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Loans and Loans Held for Sale - Additional Information (Detail) | 3 Months Ended |  |
--- | --- | --- | ---
Mar. 31, 2016 USD ($) contract | Mar. 31, 2015 USD ($) | Dec. 31, 2015 USD ($) | Mar. 04, 2015 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans, unearned income | $ 3,700,000 |  | $ 3,200,000 |
Discount on loans related to purchase accounting fair value adjustments | 10,400,000 |  | $ 10,900,000 |
Decrease in loans held for sale during the period | 23,600,000 |  |  |
Gain on sale of credit card portfolio | $ 2,066,000 | $ 0 |  |
Percentage of commercial loans in total portfolio loans | 77.00% |  | 76.00% |
Concentration Risk, Product | 0 |  |  |
Maximum concentration of commercial real estate and commercial construction portfolio in loans (in excess of) | 7.00% |  | 7.00% |
Commitment to lend additional funds on troubled debt restructuring | $ 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 |  |  |
Loans modified not considered to be troubled debt restructuring | $ 2,200,000 |  |  |
Integrity Bancshares, Inc. |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Discount on loans related to purchase accounting fair value adjustments |  |  |  | $ 14,800,000
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] |  |  |  |
Combined percentage of commercial real estate and commercial construction in total commercial loans | 66.00% |  | 67.00% |
Combined percentage of commercial real estate and commercial construction in total portfolio loans | 51.00% |  | 51.00% |
Out of market exposure of combined portfolio (percent) | 5.40% |  | 5.80% |
Percentage of total loans out-of-state excluding contiguous states | 2.70% |  | 3.00% |
Commercial |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Commercial Loans | $ 3,973,643,000 |  | $ 3,836,877,000 |
Commercial | Commercial Real Estate and Commercial Construction |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Commercial Loans | 2,600,000,000 |  |  |
Consumer |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Commercial Loans | $ 1,203,105,000 |  | $ 1,190,735,000 |

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