Schedule IV - Mortgage Loans on Real Estate (Details) - Conventional Mortgage Loan [Member] $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($)
Mortgage Loans on Real Estate [Line Items]
Face Amount of Mortgages	$ 24,776
Carrying Amount of Mortgages	22,764
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0
Mt. Airy, MD [Member] | Bank of America, N.A. [Member]
Mortgage Loans on Real Estate [Line Items]
Interest Rate	6.42%
Face Amount of Mortgages	$ 2,598
Carrying Amount of Mortgages	2,836
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0
Evansville, IN [Member] | CVS Caremark Corporation [Member]
Mortgage Loans on Real Estate [Line Items]
Interest Rate	6.22%
Face Amount of Mortgages	$ 2,670
Carrying Amount of Mortgages	2,934
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0
Greensboro, GA [Member] | CVS Caremark Corporation [Member]
Mortgage Loans on Real Estate [Line Items]
Interest Rate	6.52%
Face Amount of Mortgages	$ 1,002
Carrying Amount of Mortgages	1,116
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0
Shelby Twp., MI [Member] | CVS Caremark Corporation [Member]
Mortgage Loans on Real Estate [Line Items]
Interest Rate	5.98%
Face Amount of Mortgages	$ 2,022
Carrying Amount of Mortgages	2,177
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0
Bensalem, PA [Member] | Koninilijke Ahold N.V. [Member]
Mortgage Loans on Real Estate [Line Items]
Interest Rate	7.24%
Face Amount of Mortgages	$ 1,489
Carrying Amount of Mortgages	1,617
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0
Framingham, MA [Member] | Lowes Companies, Inc. [Member]
Mortgage Loans on Real Estate [Line Items]
Interest Rate	5.87%
Face Amount of Mortgages	$ 5,872
Carrying Amount of Mortgages	1,944
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0
Dallas, TX [Member] | Walgreen Co. [Member]
Mortgage Loans on Real Estate [Line Items]
Interest Rate	6.46%
Face Amount of Mortgages	$ 2,517
Carrying Amount of Mortgages	2,796
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0
Nacogdoches, TX [Member] | Walgreen Co. [Member]
Mortgage Loans on Real Estate [Line Items]
Interest Rate	6.80%
Face Amount of Mortgages	$ 2,758
Carrying Amount of Mortgages	3,116
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0
Rosemead, CA [Member] | Walgreen Co. [Member]
Mortgage Loans on Real Estate [Line Items]
Interest Rate	6.26%
Face Amount of Mortgages	$ 3,848
Carrying Amount of Mortgages	4,228
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0