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Loans - Troubled Debt Restructurings (Detail) - USD ($) $ in Thousands | 9 Months Ended
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Sep. 30, 2019 | Sep. 30, 2018
Financing Receivable, Modifications [Line Items] |  |
Balance at time of restructuring | $ 13,425 | $ 15,911
Balance at period end | 11,805 | 0
Commercial Portfolio Segment [Member] |  |
Financing Receivable, Modifications [Line Items] |  |
Balance at time of restructuring | 3,845 | 2,203
Balance at period end | 2,188 | 0
Commercial and industrial, Energy [Member] |  |
Financing Receivable, Modifications [Line Items] |  |
Balance at time of restructuring | 0 | 13,708
Balance at period end | 0 | 0
Commercial real estate, Buildings, land and other [Member] |  |
Financing Receivable, Modifications [Line Items] |  |
Balance at time of restructuring | 9,456 | 0
Balance at period end | 9,494 | 0
Consumer Real Estate [Member] |  |
Financing Receivable, Modifications [Line Items] |  |
Balance at time of restructuring | 124 | 0
Balance at period end | $ 123 | $ 0

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