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Loans - Troubled Debt Restructurings (Detail) - USD ($) $ in Thousands | 9 Months Ended
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Sep. 30, 2016 | Sep. 30, 2015
Financing Receivable, Modifications [Line Items] |  |
Balance at time of restructuring | $ 76,185 | $ 709
Balance at period end | 34,099 | 554
Commercial Portfolio Segment [Member] |  |
Financing Receivable, Modifications [Line Items] |  |
Balance at time of restructuring | 510 | 709
Balance at period end | 505 | 554
Commercial and industrial, Energy [Member] |  |
Financing Receivable, Modifications [Line Items] |  |
Balance at time of restructuring | 73,977 | 0
Balance at period end | 31,918 | 0
Commercial real estate, Buildings, land and other [Member] |  |
Financing Receivable, Modifications [Line Items] |  |
Balance at time of restructuring | 1,455 | 0
Balance at period end | 1,455 | 0
Construction Loans [Member] |  |
Financing Receivable, Modifications [Line Items] |  |
Balance at time of restructuring | 243 | 0
Balance at period end | $ 221 | $ 0

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- Definition Post-modification amount of investment in financing receivables modified by troubled debt restructurings. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 33 -URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953676-111524 + Details
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