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Loans - Troubled Debt Restructurings (Detail) - USD ($) $ in Thousands | 3 Months Ended
--- | ---
Mar. 31, 2017 | Mar. 31, 2016
Financing Receivable, Modifications [Line Items] |  |
Balance at time of restructuring | $ 11,262 | $ 62,808
Balance at period end | 11,212 | 61,347
Commercial Portfolio Segment [Member] |  |
Financing Receivable, Modifications [Line Items] |  |
Balance at time of restructuring | 0 | 19
Balance at period end | 0 | 17
Commercial and industrial, Energy [Member] |  |
Financing Receivable, Modifications [Line Items] |  |
Balance at time of restructuring | 11,262 | 62,546
Balance at period end | 11,212 | 61,095
Construction Loans [Member] |  |
Financing Receivable, Modifications [Line Items] |  |
Balance at time of restructuring | 0 | 243
Balance at period end | $ 0 | $ 235

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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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