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Loans - Additional Information (Detail) $ in Thousands | 3 Months Ended |  |
--- | --- | --- | ---
Mar. 31, 2017 USD ($) Item | Mar. 31, 2016 USD ($) | Feb. 28, 2017 | Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Concentration of loans in a single industry in excess of ten percent | 0.00% |  |  |
Maximum percentage loan related to single industry | 10.00% |  |  |
Percentage of total energy loans to total loans | 11.20% |  |  | 11.60%
Troubled debt restructurings | $ 11,212 | $ 61,347 |  |
Number Of Loans Restructured During The Last Year In Excess of 90 Days Past Due | Item | 1 |  |  |
Previously Restructured Loans Past Due | $ 747 |  |  |
Minimum Number Of Days To Be Considered Past Due | 90 days |  |  |
Amount charged off of previously restructured loans | $ 2,000 |  |  |
Proceeds from sale of loans | 0 | 0 |  |
Texas Leading Index economic condition indicator |  |  | 123.4 | 123.1
Commercial and industrial, Energy [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Troubled debt restructurings | 11,212 | 61,095 |  |
Non-Accrual Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Troubled debt restructurings | 11,200 |  |  |
Additional interest that would have been recognized on non-accrual loans, net of tax | 851 | $ 844 |  |
Commitments to Extend Credit [Member] | Commercial and industrial, Energy [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Unfunded balances | 1,200,000 |  |  |
Standby Letters of Credit [Member] | Commercial and industrial, Energy [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Unfunded balances | $ 38,400 |  |  |

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