Fair Value Measurements - Summary of Carrying Amounts and Corresponding Fair Values for Financial Instruments (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities—held-to-maturity	$ 589,601	$ 621,654
Fixed maturity securities—available-for-sale	369,890	414,279
Equity securities	55,375	43,437
Short-term investments	129,109	45,898
Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities—held-to-maturity	558,431	585,130
Fixed maturity securities—available-for-sale	369,890	414,279
Equity securities	55,375	43,437
Short-term investments	129,109	45,898
Cash and cash equivalents	57,541	61,757
Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities—held-to-maturity	589,601	621,654
Fixed maturity securities—available-for-sale	369,890	414,279
Equity securities	55,375	43,437
Short-term investments	129,109	45,898
Cash and cash equivalents	$ 57,541	$ 61,757