Fair Value of Financial Instruments - Carrying Value of Commercial Mortgage Loans and Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2023	Sep. 30, 2023	Dec. 31, 2022
Financing Receivable, Credit Quality Indicator [Line Items]
Total amortized cost		$ 45,589	$ 37,947
Allowance for mortgage loan losses		(55)	(49)
Mortgage loans, net		45,534	37,898
Total mortgage loans | Mortgage Loans by Region
Financing Receivable, Credit Quality Indicator [Line Items]
Mortgage loans, net		$ 45,589	$ 37,947
Percent of Total		100.00%	100.00%
Total mortgage loans | Mortgage Loans by Region | East North Central
Financing Receivable, Credit Quality Indicator [Line Items]
Mortgage loans, net		$ 3,245	$ 3,245
Percent of Total		7.10%	8.60%
Total mortgage loans | Mortgage Loans by Region | Southern Atlantic
Financing Receivable, Credit Quality Indicator [Line Items]
Mortgage loans, net		$ 17,265	$ 9,397
Percent of Total		37.80%	24.70%
Total mortgage loans | Mortgage Loans by Region | East South Central
Financing Receivable, Credit Quality Indicator [Line Items]
Mortgage loans, net		$ 7,591	$ 7,783
Percent of Total		16.70%	20.50%
Total mortgage loans | Mortgage Loans by Region | New England
Financing Receivable, Credit Quality Indicator [Line Items]
Mortgage loans, net		$ 6,588	$ 6,588
Percent of Total		14.50%	17.40%
Total mortgage loans | Mortgage Loans by Region | Middle Atlantic
Financing Receivable, Credit Quality Indicator [Line Items]
Mortgage loans, net		$ 6,020	$ 6,139
Percent of Total		13.20%	16.20%
Total mortgage loans | Mortgage Loans by Region | Mountain
Financing Receivable, Credit Quality Indicator [Line Items]
Mortgage loans, net		$ 1,992	$ 1,992
Percent of Total		4.40%	5.20%
Total mortgage loans | Mortgage Loans by Region | West North Central
Financing Receivable, Credit Quality Indicator [Line Items]
Mortgage loans, net		$ 2,888	$ 2,803
Percent of Total		6.30%	7.40%
Total mortgage loans | Mortgage Loans by Property Type
Financing Receivable, Credit Quality Indicator [Line Items]
Mortgage loans, net		$ 45,589	$ 37,947
Percent of Total	100.00%	100.00%
Total mortgage loans | Mortgage Loans by Property Type | Multifamily
Financing Receivable, Credit Quality Indicator [Line Items]
Mortgage loans, net		$ 8,536	8,493
Percent of Total	22.40%	18.70%
Total mortgage loans | Mortgage Loans by Property Type | Office
Financing Receivable, Credit Quality Indicator [Line Items]
Mortgage loans, net		$ 11,030	11,267
Percent of Total	29.70%	24.30%
Total mortgage loans | Mortgage Loans by Property Type | Industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Mortgage loans, net		$ 10,003	10,056
Percent of Total	26.50%	21.90%
Total mortgage loans | Mortgage Loans by Property Type | Retail
Financing Receivable, Credit Quality Indicator [Line Items]
Mortgage loans, net		$ 10,000	1,992
Percent of Total	5.20%	21.90%
Total mortgage loans | Mortgage Loans by Property Type | Mixed use/Other
Financing Receivable, Credit Quality Indicator [Line Items]
Mortgage loans, net		$ 6,020	6,139
Percent of Total	16.20%	13.20%
Less than 65%
Financing Receivable, Credit Quality Indicator [Line Items]
Total amortized cost		$ 36,883	29,231
65%-75%
Financing Receivable, Credit Quality Indicator [Line Items]
Total amortized cost		$ 8,706	$ 8,716