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Loans (Net (Charge-Offs)/Recoveries, Segregated by Class of Loans) (Detail) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Net charge-offs | $ (33,724) | $ (44,845) | $ (33,141)
Commercial Portfolio Segment [Member] |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Net charge-offs | (10,131) | (22,388) | (17,453)
Commercial and Industrial Total Energy Loans [Member] |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Net charge-offs | (6,058) | (13,121) | (10,009)
Commercial Real Estate, Buildings, Land and Other [Member] |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Net charge-offs | (830) | (263) | 735
Construction Loans [Member] |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Net charge-offs | 24 | 13 | 11
Total consumer real estate loans [Member] |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Net charge-offs | (2,457) | (1,538) | (506)
Consumer Loan [Member] |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Net charge-offs | $ (14,272) | $ (7,548) | $ (5,919)

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