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Investments - Gross Unrealized Gains and Losses and Cost or Amortized Cost and Fair Value of Investments Classified as Available-for-Sale (Detail) - USD ($) $ in Thousands | Dec. 31, 2018 | Dec. 31, 2017
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Investment [Line Items] |  |
Fixed maturity, Cost or Amortized Cost | $ 479,772 | $ 461,236
Fixed maturity, Gross Unrealized Gains | 3,758 | 7,072
Fixed maturity, Gross Unrealized Losses | (4,800) | (2,714)
Fixed maturity, Fair Value | 478,730 | 465,594
Equity securities, Cost or Amortized Cost | 19,962 | 8,503
Equity securities, Gross Unrealized Gains | 30 | 779
Equity securities, Gross Unrealized Losses | (1,341) |
Equity securities, Fair Value | 18,651 | 9,282
Totals, Cost or Amortized Cost |  | 469,739
Totals, Gross Unrealized Gains |  | 7,851
Totals, Gross Unrealized Losses |  | (2,714)
Totals, Fair Value |  | 474,876
States and Political Subdivisions [Member] |  |
Investment [Line Items] |  |
Fixed maturity, Cost or Amortized Cost | 231,848 | 244,898
Fixed maturity, Gross Unrealized Gains | 3,515 | 6,819
Fixed maturity, Gross Unrealized Losses | (2,118) | (577)
Fixed maturity, Fair Value | 233,245 | 251,140
Corporate Bonds [Member] |  |
Investment [Line Items] |  |
Fixed maturity, Cost or Amortized Cost | 173,904 | 130,210
Fixed maturity, Gross Unrealized Gains | 243 | 224
Fixed maturity, Gross Unrealized Losses | (933) | (212)
Fixed maturity, Fair Value | 173,214 | 130,222
U.S. Agency-Based Mortgage-Backed Securities [Member] |  |
Investment [Line Items] |  |
Fixed maturity, Cost or Amortized Cost | 12,835 | 18,813
Fixed maturity, Gross Unrealized Losses | (320) | (799)
Fixed maturity, Fair Value | 12,515 | 18,014
U.S. Treasury Securities and Obligations of U.S. Government Agencies [Member] |  |
Investment [Line Items] |  |
Fixed maturity, Cost or Amortized Cost | 61,185 | 67,315
Fixed maturity, Gross Unrealized Gains |  | 29
Fixed maturity, Gross Unrealized Losses | (1,429) | (1,126)
Fixed maturity, Fair Value | $ 59,756 | $ 66,218

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