Investments - Commercial Loan Participations, Allowance for Credit Loss (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member	us-gaap:AccountingStandardsUpdate201602Member	us-gaap:AccountingStandardsUpdate201613Member
Commercial mortgage participations
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans past due, allowance	$ 1,000		$ 1,000
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses beginning balance	335	$ 0	0	$ 0
Provision for credit losses	3,503	0	3,503	0
Securities charge-off	0	0	0	0
Recoveries	0	0	0	0
Allowance for credit losses ending balance	3,838	0	3,838	0
Commercial mortgage participations | Cumulative Effect, Period Of Adoption, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses beginning balance	$ 0	$ 0	335	$ 0
Commercial mortgage participations | Cumulative Effect, Period of Adoption, Adjustment, Net of Tax
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses beginning balance			$ 265