Investments - Narrative (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2022 USD ($) issuer	Jun. 30, 2021 USD ($)	Jun. 30, 2022 USD ($) issuer	Jun. 30, 2021 USD ($)	Dec. 31, 2021 USD ($)
Gain (Loss) on Securities [Line Items]
Fixed maturity securities, available-for-sale	$ 1,597,695,000		$ 1,597,695,000		$ 1,677,561,000
Bank loan participations	159,885,000		159,885,000		156,043,000
Unpaid principal balance	175,800,000		175,800,000
Net investment income	14,705,000	$ 14,348,000	30,972,000	$ 29,437,000
Net gain (loss) in bank loan participations	(9,895,000)	1,937,000	(11,993,000)	5,785,000
Losses due to credit-related impairments	0	0	0	0
Bank Loan Participations
Gain (Loss) on Securities [Line Items]
Net investment income	$ 2,700,000	$ 2,500,000	$ 5,100,000	$ 5,400,000
Fixed maturity securities
Gain (Loss) on Securities [Line Items]
Number of issuers | issuer	528		528
Total fair value	$ 1,445,310,000		$ 1,445,310,000		617,605,000
Gross unrealized losses	132,102,000		132,102,000		12,557,000
Fixed maturity securities, available-for-sale	1,597,695,000		1,597,695,000		1,677,561,000
Aggregate net unrealized loss	$ 132,102,000		$ 132,102,000		$ 12,557,000
Fixed maturity securities | BBB- or better
Gain (Loss) on Securities [Line Items]
Percentage of available for sale securities	99.60%		99.60%
Fixed maturity securities | Below BBB-
Gain (Loss) on Securities [Line Items]
Fixed maturity securities, available-for-sale	$ 6,700,000		$ 6,700,000
Aggregate net unrealized loss	$ 237,000		$ 237,000