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Loans - Troubled Debt Restructurings (Detail) - USD ($) $ in Thousands | 6 Months Ended
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Jun. 30, 2019 | Jun. 30, 2018
Financing Receivable, Modifications [Line Items] |  |
Balance at time of restructuring | $ 8,024 | $ 15,911
Balance at period end | 7,863 | 843
Commercial Portfolio Segment [Member] |  |
Financing Receivable, Modifications [Line Items] |  |
Balance at time of restructuring | 677 | 2,203
Balance at period end | 555 | 843
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 | 7,347 | 0
Balance at period end | $ 7,308 | $ 0

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