Investments - Commercial Mortgage Loan Participations (Details) - Commercial mortgage participations - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Investment [Line Items]
Carrying value, gross	$ 137,692	$ 96,266
Valuation allowance	0	0
Carrying value, net of valuation allowance	$ 137,692	$ 96,266
Carrying value, gross, percent	100.00%	100.00%
Valuation allowance, percent	0.00%	0.00%
Carrying value, net of valuation allowance, percent	100.00%	100.00%
South Atlantic
Investment [Line Items]
Carrying value, gross	$ 50,867	$ 39,414
Carrying value, gross, percent	37.00%	41.00%
Pacific
Investment [Line Items]
Carrying value, gross	$ 36,546	$ 20,843
Carrying value, gross, percent	27.00%	22.00%
Middle Atlantic
Investment [Line Items]
Carrying value, gross	$ 25,328	$ 23,488
Carrying value, gross, percent	18.00%	24.00%
East North Central
Investment [Line Items]
Carrying value, gross	$ 10,568	$ 10,531
Carrying value, gross, percent	8.00%	11.00%
West South Central
Investment [Line Items]
Carrying value, gross	$ 8,072	$ 1,990
Carrying value, gross, percent	6.00%	2.00%
East South Central
Investment [Line Items]
Carrying value, gross	$ 4,676	$ 0
Carrying value, gross, percent	3.00%	0.00%
New England
Investment [Line Items]
Carrying value, gross	$ 1,635	$ 0
Carrying value, gross, percent	1.00%	0.00%
Office
Investment [Line Items]
Carrying value, gross	$ 42,350	$ 35,289
Carrying value, gross, percent	31.00%	37.00%
Mixed use
Investment [Line Items]
Carrying value, gross	$ 27,501	$ 11,309
Carrying value, gross, percent	20.00%	12.00%
Hospitality
Investment [Line Items]
Carrying value, gross	$ 22,324	$ 15,137
Carrying value, gross, percent	16.00%	16.00%
Industrial
Investment [Line Items]
Carrying value, gross	$ 17,612	$ 13,896
Carrying value, gross, percent	13.00%	14.00%
Retail
Investment [Line Items]
Carrying value, gross	$ 17,318	$ 12,934
Carrying value, gross, percent	12.00%	13.00%
Multi-family
Investment [Line Items]
Carrying value, gross	$ 10,587	$ 7,701
Carrying value, gross, percent	8.00%	8.00%