Investments - Commercial Mortgage Loan Participations (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Investment [Line Items]
Carrying value, net of valuation allowance, percent	100.00%	100.00%
Commercial mortgage participations
Investment [Line Items]
Carrying value, gross	$ 96,266	$ 39,489
Valuation allowance	0	0
Carrying value, net of valuation allowance	$ 96,266	$ 39,489
Carrying value, gross, percent	100.00%	100.00%
Valuation allowance, percent	0.00%	0.00%
Carrying value, net of valuation allowance, percent	100.00%	100.00%
Office \| Commercial mortgage participations
Investment [Line Items]
Carrying value, gross	$ 35,289	$ 18,378
Carrying value, gross, percent	37.00%	46.00%
Hospitality \| Commercial mortgage participations
Investment [Line Items]
Carrying value, gross	$ 15,137	$ 10,496
Carrying value, gross, percent	16.00%	27.00%
Industrial \| Commercial mortgage participations
Investment [Line Items]
Carrying value, gross	$ 13,896	$ 0
Carrying value, gross, percent	14.00%	0.00%
Retail \| Commercial mortgage participations
Investment [Line Items]
Carrying value, gross	$ 12,934	$ 0
Carrying value, gross, percent	13.00%	0.00%
Mixed use \| Commercial mortgage participations
Investment [Line Items]
Carrying value, gross	$ 11,309	$ 7,148
Carrying value, gross, percent	12.00%	18.00%
Multi-family \| Commercial mortgage participations
Investment [Line Items]
Carrying value, gross	$ 7,701	$ 3,467
Carrying value, gross, percent	8.00%	9.00%
South Atlantic \| Commercial mortgage participations
Investment [Line Items]
Carrying value, gross	$ 39,414	$ 18,378
Carrying value, gross, percent	41.00%	46.00%
Middle Atlantic \| Commercial mortgage participations
Investment [Line Items]
Carrying value, gross	$ 23,488	$ 3,467
Carrying value, gross, percent	24.00%	9.00%
Pacific \| Commercial mortgage participations
Investment [Line Items]
Carrying value, gross	$ 20,843	$ 7,148
Carrying value, gross, percent	22.00%	18.00%
East North Central \| Commercial mortgage participations
Investment [Line Items]
Carrying value, gross	$ 10,531	$ 10,496
Carrying value, gross, percent	11.00%	27.00%
West South Central \| Commercial mortgage participations
Investment [Line Items]
Carrying value, gross	$ 1,990	$ 0
Carrying value, gross, percent	2.00%	0.00%

Line items represent reporting concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
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-Name Accounting Standards Codification
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