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Comprehensive Income and Accumulated Other Comprehensive Income - Other Comprehensive Income (Detail) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Equity [Abstract] |  |  |
Unrealized gain (loss) on available-for-sale securities, Pre-tax Amount | $ 6,960 | $ (4,908) | $ (2,572)
Change in unrealized losses on available-for-sale securities with OTTI, Pre-Tax Amount |  |  | 176
Less amortization of differences between fair value and amortized cost for fixed maturity security transfer, Pre-tax Amount |  | (63) | (40)
Reclassification adjustment for gains (losses) realized in net income, Pre-Tax Amount | (1,106) | 234 | 2,093
Net unrealized gain loss, Pre-Tax Amount | 5,854 | (4,737) | (343)
Other comprehensive income (loss), Pre-Tax Amount | 5,854 | (4,737) | (343)
Unrealized gain loss on available-for-sale securities, Tax Expense | 2,137 | (1,718) | (900)
Change in unrealized losses on available-for-sale securities with OTTI, Tax Expense |  |  | 62
Less amortization of differences between fair value and amortized cost for fixed maturity security transfer, Tax Expense |  | (22) | (14)
Reclassification adjustment for gains (losses) realized in net income, Tax Expense | (387) | 82 | 732
Net unrealized gain loss, Tax Expense | 1,750 | (1,658) | (120)
Other comprehensive income (loss), Tax Expense | 1,750 | (1,658) | (120)
Unrealized gain (loss) on available-for-sale securities, Net-of-Tax Amount | 4,823 | (3,190) | (1,672)
Change in unrealized losses on available-for-sale securities with OTTI, Net-of-Tax Amount |  |  | 114
Less amortization of differences between fair value and amortized cost for fixed maturity security transfer, Net-of-Tax Amount |  | (41) | (26)
Reclassification adjustment for gains (losses) realized in net income, Net-of-Tax Amount | (719) | 152 | 1,361
Net unrealized gain loss, Net-of-Tax Amount | 4,104 | (3,079) | (223)
Other comprehensive income (loss), Net-of-Tax Amount | $ 4,104 | $ (3,079) | $ (223)

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- Definition Amount after tax of reclassification adjustment from accumulated other comprehensive income for unrealized gain (loss) realized upon the sale of available-for-sale securities and other than temporary impairment charges. + References No definition available. + Details
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- Definition Amount of tax expense (benefit) of reclassification adjustment from accumulated other comprehensive income for unrealized gain (loss) realized upon the sale of available-for-sale securities and other than temporary impairment charges. + References No definition available. + Details
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- Definition Amortization of unrealized gain (loss) remaining from transfer of securities from available for sale to held to maturity, net of tax. + References No definition available. + Details
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