Fair Value of Financial Instruments (Carrying Value of Commercial Mortgage Loans and Additional Information) (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Financing Receivable, Credit Quality Indicator [Line Items]
Total amortized cost	$ 36,374	$ 25,828
Allowance allowance	(62)	(46)
Carrying Value	36,312	25,782
Total mortgage loans | Mortgage Loans by Region
Financing Receivable, Credit Quality Indicator [Line Items]
Carrying Value	$ 36,374	$ 25,828
Percent of Total	100.00%	100.00%
Total mortgage loans | Mortgage Loans by Region | East North Central
Financing Receivable, Credit Quality Indicator [Line Items]
Carrying Value	$ 3,245	$ 3,244
Percent of Total	8.90%	12.60%
Total mortgage loans | Mortgage Loans by Region | Southern Atlantic
Financing Receivable, Credit Quality Indicator [Line Items]
Carrying Value	$ 6,652	$ 6,652
Percent of Total	18.30%	25.80%
Total mortgage loans | Mortgage Loans by Region | East South Central
Financing Receivable, Credit Quality Indicator [Line Items]
Carrying Value	$ 4,861	$ 4,975
Percent of Total	13.40%	19.30%
Total mortgage loans | Mortgage Loans by Region | New England
Financing Receivable, Credit Quality Indicator [Line Items]
Carrying Value	$ 6,588	$ 6,588
Percent of Total	18.10%	25.40%
Total mortgage loans | Mortgage Loans by Region | Middle Atlantic
Financing Receivable, Credit Quality Indicator [Line Items]
Carrying Value	$ 12,801	$ 4,369
Percent of Total	35.20%	16.90%
Total mortgage loans | Mortgage Loans by Region | Mountain
Financing Receivable, Credit Quality Indicator [Line Items]
Carrying Value	$ 2,227	$ 0
Percent of Total	6.10%	0.00%
Total mortgage loans | Property Type Concentration Risk
Financing Receivable, Credit Quality Indicator [Line Items]
Carrying Value	$ 36,374	$ 25,828
Percent of Total	100.00%	100.00%
Total mortgage loans | Property Type Concentration Risk | Multifamily
Financing Receivable, Credit Quality Indicator [Line Items]
Carrying Value	$ 3,245	$ 3,244
Percent of Total	8.90%	12.60%
Total mortgage loans | Property Type Concentration Risk | Office
Financing Receivable, Credit Quality Indicator [Line Items]
Carrying Value	$ 11,513	$ 11,627
Percent of Total	31.70%	45.00%
Total mortgage loans | Property Type Concentration Risk | Retail
Financing Receivable, Credit Quality Indicator [Line Items]
Carrying Value	$ 2,227	$ 0
Percent of Total	6.10%	0.00%
Total mortgage loans | Property Type Concentration Risk | Mixed use/Other
Financing Receivable, Credit Quality Indicator [Line Items]
Carrying Value	$ 19,389	$ 10,957
Percent of Total	53.30%	42.40%
Less than 65%
Financing Receivable, Credit Quality Indicator [Line Items]
Total amortized cost	$ 27,878	$ 25,828
65%-75%
Financing Receivable, Credit Quality Indicator [Line Items]
Total amortized cost	$ 8,496	$ 0