Fair Value Measurements - Summary of Assets Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Fixed maturity securities, available-for-sale:
Total fixed maturity securities, available-for-sale	$ 1,597,695	$ 1,677,561
Equity securities:
Bank loan participations	159,885	156,043
Short-term investments	130,435	136,563
Fixed maturity securities
Fixed maturity securities, available-for-sale:
Total fixed maturity securities, available-for-sale	1,597,695	1,677,561
State and municipal
Fixed maturity securities, available-for-sale:
Total fixed maturity securities, available-for-sale	302,405	333,717
Residential mortgage-backed
Fixed maturity securities, available-for-sale:
Total fixed maturity securities, available-for-sale	290,555	246,631
Corporate
Fixed maturity securities, available-for-sale:
Total fixed maturity securities, available-for-sale	606,821	732,335
Commercial mortgage and asset-backed
Fixed maturity securities, available-for-sale:
Total fixed maturity securities, available-for-sale	322,204	304,488
U.S. Treasury securities and obligations guaranteed by the U.S. government
Fixed maturity securities, available-for-sale:
Total fixed maturity securities, available-for-sale	75,710	60,390
Recurring basis
Equity securities:
Bank loan participations	159,885	156,043
Short-term investments	130,435	136,563
Recurring basis | Fixed maturity securities
Fixed maturity securities, available-for-sale:
Total fixed maturity securities, available-for-sale	1,597,695	1,677,561
Recurring basis | State and municipal
Fixed maturity securities, available-for-sale:
Total fixed maturity securities, available-for-sale	302,405	333,717
Recurring basis | Residential mortgage-backed
Fixed maturity securities, available-for-sale:
Total fixed maturity securities, available-for-sale	290,555	246,631
Recurring basis | Corporate
Fixed maturity securities, available-for-sale:
Total fixed maturity securities, available-for-sale	606,821	732,335
Recurring basis | Commercial mortgage and asset-backed
Fixed maturity securities, available-for-sale:
Total fixed maturity securities, available-for-sale	322,204	304,488
Recurring basis | U.S. Treasury securities and obligations guaranteed by the U.S. government
Fixed maturity securities, available-for-sale:
Total fixed maturity securities, available-for-sale	75,710	60,390
Recurring basis | Equity securities
Equity securities:
Total equity securities	98,653	108,410
Recurring basis | Preferred stock
Equity securities:
Total equity securities	51,750	63,612
Recurring basis | Common stock
Equity securities:
Total equity securities	46,903	44,798
Recurring basis | Quoted Prices in Active Markets for Identical Assets Level 1
Equity securities:
Bank loan participations	0	0
Short-term investments	0	0
Recurring basis | Quoted Prices in Active Markets for Identical Assets Level 1 | Fixed maturity securities
Fixed maturity securities, available-for-sale:
Total fixed maturity securities, available-for-sale	75,356	59,988
Recurring basis | Quoted Prices in Active Markets for Identical Assets Level 1 | State and municipal
Fixed maturity securities, available-for-sale:
Total fixed maturity securities, available-for-sale	0	0
Recurring basis | Quoted Prices in Active Markets for Identical Assets Level 1 | Residential mortgage-backed
Fixed maturity securities, available-for-sale:
Total fixed maturity securities, available-for-sale	0	0
Recurring basis | Quoted Prices in Active Markets for Identical Assets Level 1 | Corporate
Fixed maturity securities, available-for-sale:
Total fixed maturity securities, available-for-sale	0	0
Recurring basis | Quoted Prices in Active Markets for Identical Assets Level 1 | Commercial mortgage and asset-backed
Fixed maturity securities, available-for-sale:
Total fixed maturity securities, available-for-sale	0	0
Recurring basis | Quoted Prices in Active Markets for Identical Assets Level 1 | U.S. Treasury securities and obligations guaranteed by the U.S. government
Fixed maturity securities, available-for-sale:
Total fixed maturity securities, available-for-sale	75,356	59,988
Recurring basis | Quoted Prices in Active Markets for Identical Assets Level 1 | Equity securities
Equity securities:
Total equity securities	43,470	41,244
Recurring basis | Quoted Prices in Active Markets for Identical Assets Level 1 | Preferred stock
Equity securities:
Total equity securities	0	0
Recurring basis | Quoted Prices in Active Markets for Identical Assets Level 1 | Common stock
Equity securities:
Total equity securities	43,470	41,244
Recurring basis | Significant Other Observable Inputs Level 2
Equity securities:
Bank loan participations	159,885	156,043
Short-term investments	130,435	136,563
Recurring basis | Significant Other Observable Inputs Level 2 | Fixed maturity securities
Fixed maturity securities, available-for-sale:
Total fixed maturity securities, available-for-sale	1,522,339	1,617,573
Recurring basis | Significant Other Observable Inputs Level 2 | State and municipal
Fixed maturity securities, available-for-sale:
Total fixed maturity securities, available-for-sale	302,405	333,717
Recurring basis | Significant Other Observable Inputs Level 2 | Residential mortgage-backed
Fixed maturity securities, available-for-sale:
Total fixed maturity securities, available-for-sale	290,555	246,631
Recurring basis | Significant Other Observable Inputs Level 2 | Corporate
Fixed maturity securities, available-for-sale:
Total fixed maturity securities, available-for-sale	606,821	732,335
Recurring basis | Significant Other Observable Inputs Level 2 | Commercial mortgage and asset-backed
Fixed maturity securities, available-for-sale:
Total fixed maturity securities, available-for-sale	322,204	304,488
Recurring basis | Significant Other Observable Inputs Level 2 | U.S. Treasury securities and obligations guaranteed by the U.S. government
Fixed maturity securities, available-for-sale:
Total fixed maturity securities, available-for-sale	354	402
Recurring basis | Significant Other Observable Inputs Level 2 | Equity securities
Equity securities:
Total equity securities	55,183	67,064
Recurring basis | Significant Other Observable Inputs Level 2 | Preferred stock
Equity securities:
Total equity securities	51,750	63,612
Recurring basis | Significant Other Observable Inputs Level 2 | Common stock
Equity securities:
Total equity securities	3,433	3,452
Recurring basis | Significant Unobservable Inputs Level 3
Equity securities:
Bank loan participations	0	0
Short-term investments	0	0
Recurring basis | Significant Unobservable Inputs Level 3 | Fixed maturity securities
Fixed maturity securities, available-for-sale:
Total fixed maturity securities, available-for-sale	0	0
Recurring basis | Significant Unobservable Inputs Level 3 | State and municipal
Fixed maturity securities, available-for-sale:
Total fixed maturity securities, available-for-sale	0	0
Recurring basis | Significant Unobservable Inputs Level 3 | Residential mortgage-backed
Fixed maturity securities, available-for-sale:
Total fixed maturity securities, available-for-sale	0	0
Recurring basis | Significant Unobservable Inputs Level 3 | Corporate
Fixed maturity securities, available-for-sale:
Total fixed maturity securities, available-for-sale	0	0
Recurring basis | Significant Unobservable Inputs Level 3 | Commercial mortgage and asset-backed
Fixed maturity securities, available-for-sale:
Total fixed maturity securities, available-for-sale	0	0
Recurring basis | Significant Unobservable Inputs Level 3 | U.S. Treasury securities and obligations guaranteed by the U.S. government
Fixed maturity securities, available-for-sale:
Total fixed maturity securities, available-for-sale	0	0
Recurring basis | Significant Unobservable Inputs Level 3 | Equity securities
Equity securities:
Total equity securities	0	102
Recurring basis | Significant Unobservable Inputs Level 3 | Preferred stock
Equity securities:
Total equity securities	0	0
Recurring basis | Significant Unobservable Inputs Level 3 | Common stock
Equity securities:
Total equity securities	$ 0	$ 102