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v3.19.3

Loans - Additional Information (Detail) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Sep. 30, 2019 | Sep. 30, 2018 | Sep. 30, 2019 | Sep. 30, 2018 | Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Concentration of loans in a single industry in excess of ten percent | 0.00% |  | 0.00% |  |
Maximum percentage loan related to single industry |  |  | 10.00% |  |
Percentage of total energy loans to total loans | 10.50% |  | 10.50% |  | 11.40%
Loans and Leases Receivable, Related Parties | $ 326.1 |  | $ 326.1 |  | $ 256.1
Interest income recognized subsequent to classification as impaired |  |  | $ 0.0 |  | $ 0.0
Texas Leading Index economic condition indicator | 128.1 |  | 128.1 |  | 126.4
Non Accrual Loans [Member] |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Additional interest that would have been recognized on non-accrual loans, net of tax | $ 0.9 | $ 1.3 | $ 3.0 | $ 4.2 |
Commitments to Extend Credit [Member] | Commercial and industrial, Energy [Member] |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Unfunded balances | 1,300.0 |  | 1,300.0 |  |
Standby Letters of Credit [Member] | Commercial and industrial, Energy [Member] |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Unfunded balances | $ 66.1 |  | $ 66.1 |  |

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