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Activity in Allowance for Losses on Non-Covered Loans (Parenthetical) (Detail) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2016 | Dec. 31, 2015
Am Trust Bank and Desert Hills Bank |  |
Valuation Allowance [Line Items] |  |
Allowance associated on loans acquired | $ 14.2 | $ 14.2

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- Definition Amount of addition to allowance reserve for credit loss arising from purchase of loan and lease portfolios. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 15 -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 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.7(d)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
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Balance Type: | credit
Period Type: | duration

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Details
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Balance Type: |
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