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Activity in Allowance for Losses on Covered Loans (Detail) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Valuation Allowance [Line Items] |  |  |
Balance, beginning of period | $ 23,701 | $ 31,395 |
Recovery of losses on covered loans | 37,242 | 4,180 | $ (15,004)
Balance, end of period | 0 | 23,701 | $ 31,395
Covered | Covered loans held for sale |  |  |
Valuation Allowance [Line Items] |  |  |
Recovery of losses on covered loans | $ (23,701) | $ (7,694) |

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- Definition Provision Recoveries For Loan Losses + References No definition available. + Details
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Balance Type: | debit
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- Definition Amount of allowance for loan and lease losses covered by loss sharing agreements. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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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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- Details
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Namespace Prefix: |
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Balance Type: |
Period Type: |