Investments - Commercial Mortgage Loan Participations Recorded Investment (Details) - Commercial mortgage participations - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, net of valuation allowance, percent	100.00%	100.00%
Carrying value, net of valuation allowance	$ 164,420	$ 137,692
Less than 70%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, net of valuation allowance, percent	77.00%	90.00%
Carrying value, net of valuation allowance	$ 126,155	$ 124,460
70% to 80%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, net of valuation allowance, percent	21.00%	10.00%
Carrying value, net of valuation allowance	$ 34,744	$ 13,232
81% to 90%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, net of valuation allowance, percent	0.00%	0.00%
Carrying value, net of valuation allowance	$ 0	$ 0
Greater than 90%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, net of valuation allowance, percent	2.00%	0.00%
Carrying value, net of valuation allowance	$ 3,521	$ 0
Less Than 1.00x
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, net of valuation allowance	24,633	75,605
Less Than 1.00x | Less than 70%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, net of valuation allowance	19,747	64,160
Less Than 1.00x | 70% to 80%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, net of valuation allowance	1,365	11,445
Less Than 1.00x | 81% to 90%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, net of valuation allowance	0	0
Less Than 1.00x | Greater than 90%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, net of valuation allowance	3,521	0
1.00x-1.20x
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, net of valuation allowance	139,787	49,421
1.00x-1.20x | Less than 70%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, net of valuation allowance	106,408	47,634
1.00x-1.20x | 70% to 80%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, net of valuation allowance	33,379	1,787
1.00x-1.20x | 81% to 90%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, net of valuation allowance	0	0
1.00x-1.20x | Greater than 90%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, net of valuation allowance	0	0
Greater Than 1.20x
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, net of valuation allowance	0	12,666
Greater Than 1.20x | Less than 70%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, net of valuation allowance	0	12,666
Greater Than 1.20x | 70% to 80%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, net of valuation allowance	0	0
Greater Than 1.20x | 81% to 90%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, net of valuation allowance	0	0
Greater Than 1.20x | Greater than 90%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value, net of valuation allowance	$ 0	$ 0