Investments - Summary of Securities with Gross Unrealized Loss Positions Aggregated by Investment Category (Detail) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss, Less than Twelve Months	$ (9,677)	$ (146)
Estimated Fair Value, Less than Twelve Months	294,080	14,703
Gross Unrealized Loss, Twelve Months or Longer	(700)	(13)
Estimated Fair Value, Twelve Months or Longer	7,185	616
Gross Unrealized Loss, Total	(10,377)	(159)
Estimated Fair Value, Total	301,265	15,319
Fixed-Maturity Securities [Member] | U.S. Treasury and U.S. Government Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss, Less than Twelve Months	(8,701)	(73)
Estimated Fair Value, Less than Twelve Months	269,116	9,809
Gross Unrealized Loss, Twelve Months or Longer	(404)	(13)
Estimated Fair Value, Twelve Months or Longer	4,644	616
Gross Unrealized Loss, Total	(9,105)	(86)
Estimated Fair Value, Total	273,760	10,425
Fixed-Maturity Securities [Member] | Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss, Less than Twelve Months	(909)	(53)
Estimated Fair Value, Less than Twelve Months	23,028	4,452
Gross Unrealized Loss, Twelve Months or Longer	(296)	0
Estimated Fair Value, Twelve Months or Longer	2,541	0
Gross Unrealized Loss, Total	(1,205)	(53)
Estimated Fair Value, Total	25,569	4,452
Fixed-Maturity Securities [Member] | State, Municipalities, and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss, Less than Twelve Months	(6)
Estimated Fair Value, Less than Twelve Months	1,383
Gross Unrealized Loss, Twelve Months or Longer	0
Estimated Fair Value, Twelve Months or Longer	0
Gross Unrealized Loss, Total	(6)
Estimated Fair Value, Total	1,383
Fixed-Maturity Securities [Member] | Exchange-Traded Debt [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss, Less than Twelve Months	(52)
Estimated Fair Value, Less than Twelve Months	463
Gross Unrealized Loss, Twelve Months or Longer	0
Estimated Fair Value, Twelve Months or Longer	0
Gross Unrealized Loss, Total	(52)
Estimated Fair Value, Total	463
Fixed-Maturity Securities [Member] | Redeemable Preferred Stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss, Less than Twelve Months	(9)	(20)
Estimated Fair Value, Less than Twelve Months	90	442
Gross Unrealized Loss, Twelve Months or Longer	0	0
Estimated Fair Value, Twelve Months or Longer	0	0
Gross Unrealized Loss, Total	(9)	(20)
Estimated Fair Value, Total	$ 90	$ 442