Investments - Commercial Mortgage Loan Participations (Details) - Commercial mortgage participations $ in Thousands	Dec. 31, 2020 USD ($) loan	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, gross	$ 164,107	$ 137,692
Carrying value, gross, percent	102.00%	100.00%
Allowance for credit losses	$ (3,505)	$ 0	$ 0
Allowance for credit losses, percent	(2.00%)	0.00%
Carrying value, net of valuation allowance	$ 160,602	$ 137,692
Carrying value, net, percent	100.00%	100.00%
Number of loans | loan	24
California
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, gross	$ 61,610	$ 35,412
Carrying value, gross, percent	38.00%	26.00%
Virginia
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, gross	$ 27,019	$ 25,448
Carrying value, gross, percent	17.00%	18.00%
New York
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, gross	$ 16,602	$ 21,117
Carrying value, gross, percent	10.00%	15.00%
Florida
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, gross	$ 12,420	$ 11,910
Carrying value, gross, percent	8.00%	9.00%
Pennsylvania
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, gross	$ 11,314	$ 4,211
Carrying value, gross, percent	7.00%	3.00%
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, gross	$ 35,142	$ 39,594
Carrying value, gross, percent	22.00%	29.00%
Office
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, gross	$ 36,153	$ 42,350
Carrying value, gross, percent	22.00%	31.00%
Mixed use
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, gross	$ 49,002	$ 27,501
Carrying value, gross, percent	31.00%	20.00%
Hospitality
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, gross	$ 22,605	$ 22,324
Carrying value, gross, percent	14.00%	16.00%
Industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, gross	$ 17,900	$ 17,612
Carrying value, gross, percent	11.00%	13.00%
Retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, gross	$ 19,319	$ 17,318
Carrying value, gross, percent	12.00%	12.00%
Multi-family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, gross	$ 19,128	$ 10,587
Carrying value, gross, percent	12.00%	8.00%