Investments - Commercial Mortgage Loan Participations Recorded Investment (Details) - Commercial mortgage participations - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Investment [Line Items]
Carrying value, net of valuation allowance	$ 137,692	$ 96,266
Carrying value, net of valuation allowance, percent	100.00%	100.00%
Less than 70%
Investment [Line Items]
Carrying value, net of valuation allowance	$ 124,460	$ 85,687
Carrying value, net of valuation allowance, percent	90.00%	89.00%
70% to 80%
Investment [Line Items]
Carrying value, net of valuation allowance	$ 13,232	$ 10,579
Carrying value, net of valuation allowance, percent	10.00%	11.00%
81% to 90%
Investment [Line Items]
Carrying value, net of valuation allowance	$ 0	$ 0
Carrying value, net of valuation allowance, percent	0.00%	0.00%
Greater than 90%
Investment [Line Items]
Carrying value, net of valuation allowance	$ 0	$ 0
Carrying value, net of valuation allowance, percent	0.00%	0.00%
Less Than 1.00x
Investment [Line Items]
Carrying value, net of valuation allowance	$ 75,605	$ 28,922
Less Than 1.00x | Less than 70%
Investment [Line Items]
Carrying value, net of valuation allowance	64,160	18,343
Less Than 1.00x | 70% to 80%
Investment [Line Items]
Carrying value, net of valuation allowance	11,445	10,579
Less Than 1.00x | 81% to 90%
Investment [Line Items]
Carrying value, net of valuation allowance	0	0
Less Than 1.00x | Greater than 90%
Investment [Line Items]
Carrying value, net of valuation allowance	0	0
1.00x-1.20x
Investment [Line Items]
Carrying value, net of valuation allowance	49,421	56,813
1.00x-1.20x | Less than 70%
Investment [Line Items]
Carrying value, net of valuation allowance	47,634	56,813
1.00x-1.20x | 70% to 80%
Investment [Line Items]
Carrying value, net of valuation allowance	1,787	0
1.00x-1.20x | 81% to 90%
Investment [Line Items]
Carrying value, net of valuation allowance	0	0
1.00x-1.20x | Greater than 90%
Investment [Line Items]
Carrying value, net of valuation allowance	0	0
Greater Than 1.20x
Investment [Line Items]
Carrying value, net of valuation allowance	12,666	10,531
Greater Than 1.20x | Less than 70%
Investment [Line Items]
Carrying value, net of valuation allowance	12,666	10,531
Greater Than 1.20x | 70% to 80%
Investment [Line Items]
Carrying value, net of valuation allowance	0	0
Greater Than 1.20x | 81% to 90%
Investment [Line Items]
Carrying value, net of valuation allowance	0	0
Greater Than 1.20x | Greater than 90%
Investment [Line Items]
Carrying value, net of valuation allowance	$ 0	$ 0