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Loans - Average Recorded Investment In Impaired Loans (Detail) - USD ($) $ in Thousands | 3 Months Ended
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Mar. 31, 2017 | Mar. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Average recorded investment | $ 102,283 | $ 124,650
Commercial Portfolio Segment [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Average recorded investment | 26,393 | 23,809
Commercial and industrial, Energy [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Average recorded investment | 68,101 | 67,615
Commercial real estate, Buildings, land and other [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Average recorded investment | 6,660 | 31,985
Construction Loans [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Average recorded investment | 0 | 770
Consumer Real Estate [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Average recorded investment | 1,102 | 471
Consumer and Other [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Average recorded investment | $ 27 | $ 0

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- Definition Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5212-111524 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5258-111524 + Details
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