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Investments - Gross Realized Gains and Losses on Sale of Debt Securities (Detail) - Debt Securities [Member] - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2018 | Jun. 30, 2017
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Gross realized gains | $ 25 | $ 33 | $ 25 | $ 57
Gross realized losses | $ (241) | $ (113) | $ (315) | $ (152)

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- Definition This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. + References No definition available. + Details
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- Definition This item represents the gross loss realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. + 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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- Details
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