Investments - Commercial Mortgage Loan Participations Recorded Investment (Details) - Commercial mortgage participations - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, gross	$ 162,176	$ 137,692
Carrying value, gross, percent	100.00%	100.00%
Office
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, gross	$ 42,670	$ 42,350
Carrying value, gross, percent	26.00%	31.00%
Mixed use
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, gross	$ 42,010	$ 27,501
Carrying value, gross, percent	26.00%	20.00%
Hospitality
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, gross	$ 22,602	$ 22,324
Carrying value, gross, percent	14.00%	16.00%
Industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, gross	$ 22,422	$ 17,612
Carrying value, gross, percent	14.00%	13.00%
Retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, gross	$ 18,605	$ 17,318
Carrying value, gross, percent	11.00%	12.00%
Multi-family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, gross	$ 13,867	$ 10,587
Carrying value, gross, percent	9.00%	8.00%
Less than 70%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, gross	$ 142,747	$ 124,460
Carrying value, gross, percent	88.00%	90.00%
70% to 80%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, gross	$ 14,837	$ 13,232
Carrying value, gross, percent	9.00%	10.00%
81% to 90%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, gross	$ 0	$ 0
Carrying value, gross, percent	0.00%	0.00%
Greater than 90%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, gross	$ 4,592	$ 0
Carrying value, gross, percent	3.00%	0.00%
Less Than 1.00x
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, gross	$ 79,909	$ 75,605
Less Than 1.00x | Less than 70%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, gross	62,270	64,160
Less Than 1.00x | 70% to 80%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, gross	13,047	11,445
Less Than 1.00x | 81% to 90%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, gross	0	0
Less Than 1.00x | Greater than 90%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, gross	4,592	0
1.00x-1.20x
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, gross	69,589	49,421
1.00x-1.20x | Less than 70%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, gross	67,799	47,634
1.00x-1.20x | 70% to 80%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, gross	1,790	1,787
1.00x-1.20x | 81% to 90%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, gross	0	0
1.00x-1.20x | Greater than 90%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, gross	0	0
Greater Than 1.20x
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, gross	12,678	12,666
Greater Than 1.20x | Less than 70%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, gross	12,678	12,666
Greater Than 1.20x | 70% to 80%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, gross	0	0
Greater Than 1.20x | 81% to 90%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, gross	0	0
Greater Than 1.20x | Greater than 90%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, gross	$ 0	$ 0