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Securities Held-to-Maturity - Additional Information (Detail) - Securities | 6 Months Ended | 12 Months Ended
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Jun. 30, 2019 | Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract] |  |
Number of securities determined to be other than temporarily impaired | 0 | 0

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- Definition Number of securities determined to be other than temporarily impaired. + References No definition available. + Details
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