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Servicing - Additional Information (Detail) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017
Transfers And Servicing [Abstract] |  |
Loans serviced for others unpaid principal amount | $ 289.2 | $ 288.6
Capitalized service right assets included in other assets | 2.4 | 2.3
Fair market value of the capitalized servicing rights | $ 3.3 | $ 3.1
Prepayment rate | 8.90% | 10.40%
Discount yield | 6.60% | 6.07%

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