Fair Value Measurements - Summary of Carrying Amounts and Corresponding Fair Values for Financial Instruments (Detail) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities—held-to-maturity	$ 545,425	$ 575,850
Fixed maturity securities—available-for-sale	342,972	341,769
Equity securities	69,156	64,140
Short-term investments	72,820	57,431
Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities—held-to-maturity	545,372	549,231
Fixed maturity securities—available-for-sale	342,972	341,769
Equity securities	69,156	64,140
Short-term investments	72,820	57,431
Cash and cash equivalents	30,741	70,722
Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities—held-to-maturity	545,425	575,850
Fixed maturity securities—available-for-sale	342,972	341,769
Equity securities	69,156	64,140
Short-term investments	72,820	57,431
Cash and cash equivalents	$ 30,741	$ 70,722