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Basis of Presentation - Additional Information (Detail) - USD ($) |  | 6 Months Ended |
--- | --- | --- | ---
Jan. 01, 2020 | Jun. 30, 2020 | Jun. 30, 2019 | Dec. 31, 2019
New Accounting Pronouncements Or Change In Accounting Principle [Line Items] |  |  |  |
Percentage of comparable consolidated amounts |  | 95.00% | 95.00% |
Credit allowance for held-to-maturity fixed income securities |  | $ 357,000 |  | $ 0
Credit allowance for reinsurance recoverables |  | 388,000 |  | 0
Available-for-sale securities, credit allowance |  | $ 0 |  | $ 0
Trading securities, par value per share |  | $ 100 |  |
Reinsurance recoverables, current credit rating period |  | 10 years |  |
Reinsurance treaty term to be commuted by end of current credit rating period |  | 3 years |  |
Other-than-temporary impairment loss, debt securities, portion recognized in earnings |  | $ 0 |  |
Financial assets purchased with credit deterioration, financing receivable |  | 0 |  |
Financial assets purchased with credit deterioration, held-to-maturity debt securities |  | 0 |  |
Financial assets purchased with credit deterioration, available-for-sale debt securities |  | $ 0 |  |
Threshold period for writing off balances receivable |  | 90 days |  |
Minimum [Member] |  |  |  |
New Accounting Pronouncements Or Change In Accounting Principle [Line Items] |  |  |  |
Trading price of securities excluded from watch list |  | $ 95 |  |
Corporate Fixed Income Securities [Member] | Maximum [Member] |  |  |  |
New Accounting Pronouncements Or Change In Accounting Principle [Line Items] |  |  |  |
Investments maturity period using default rate |  | 20 years |  |
Municipal Fixed Income Securities [Member] | Maximum [Member] |  |  |  |
New Accounting Pronouncements Or Change In Accounting Principle [Line Items] |  |  |  |
Investments maturity period using default rate |  | 20 years |  |
ASU 2016-13 [Member] |  |  |  |
New Accounting Pronouncements Or Change In Accounting Principle [Line Items] |  |  |  |
Net decrease to retained earnings, cumulative effect | $ 594,000 |  |  |
Credit allowance for held-to-maturity fixed income securities | 243,000 |  |  |
Credit allowance for reinsurance recoverables | $ 351,000 |  |  |

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