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Impairment of Investment Securities - Schedule of Unrealized Losses and Estimated Fair Values (Detail) - USD ($) $ in Thousands | Mar. 31, 2020 | Dec. 31, 2019
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Debt and Equity Securities, FV-NI [Line Items] |  |
Investment Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value | $ 25,481 | $ 166,470
Investment Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | (215) | (637)
Investment Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value | 0 | 235,380
Investment Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 0 | (2,950)
Investment Securities, Continuous Unrealized Loss Position, Fair Value, Total | 25,481 | 401,850
Investment Securities, Continuous Unrealized Loss Position, Accumulated Loss | (215) | (3,587)
US Government Agency Debt Securities Commercial [Domain] |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Investment Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value | 25,481 | 54,501
Investment Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | (215) | (201)
Investment Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value | 0 | 16,365
Investment Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 0 | (149)
Investment Securities, Continuous Unrealized Loss Position, Fair Value, Total | 25,481 | 70,866
Investment Securities, Continuous Unrealized Loss Position, Accumulated Loss | $ (215) | (350)
Residential Mortgage Backed Securities [Member] |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Investment Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value |  | 111,969
Investment Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss |  | (436)
Investment Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value |  | 219,015
Investment Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss |  | (2,801)
Investment Securities, Continuous Unrealized Loss Position, Fair Value, Total |  | 330,984
Investment Securities, Continuous Unrealized Loss Position, Accumulated Loss |  | $ (3,237)

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- Definition Investment Securities, Continuous Unrealized Loss Position, Accumulated Loss + References No definition available. + Details
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- Definition Investment Securities, Continuous Unrealized Loss Position, Fair Value, Total + References No definition available. + Details
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- Definition Investment Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss + References No definition available. + Details
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- Definition Investment Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value + References No definition available. + Details
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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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