Schedule IV - Mortgage Loans on Real Estate - Mortgage Loans on Real Estate (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Carrying amount		$ 7,829	$ 14,448	$ 21,838	$ 23,197
Mortgage Loans [Member]
Face amount		8,679
Carrying amount	[1]	7,387
Other Financing Loans [Member]
Face amount		9,454
Carrying amount	[1]	$ 7,828
Retail Site [Member] | Las Vegas, NV [Member] | Borrower A [Member] | Mortgage Loans [Member]
Interest rate		12.00%
Face amount		$ 3,075
Carrying amount	[1]	$ 3,075
Retail Site [Member] | Walker, MI [Member] | Borrower B [Member] | Mortgage Loans [Member]
Interest rate		4.00%
Face amount		$ 3,750
Carrying amount	[1]	$ 3,750
Nonretail [Member] | Other Financing Loans [Member] | Charlie Browns License [Member]
Interest rate		2.28%
Face amount		$ 600
Carrying amount	[1]	$ 291
Nonretail [Member] | Other Financing Loans [Member] | RONA Capital Partners [Member]
Interest rate		6.20%
Face amount		$ 175
Carrying amount	[1]	$ 150
Nonretail [Member] | Commack, NY [Member] | Borrower C [Member] | Mortgage Loans [Member]
Interest rate		7.41%
Face amount		$ 1,354
Carrying amount	[1]	$ 301
Nonretail [Member] | Melbourne, FL [Member] | Borrower D [Member]
Interest rate		6.88%
Face amount		$ 500
Carrying amount	[1]	$ 261

[1] The aggregate cost for Federal income tax purposes was approximately $7.8 million as of December 31, 2019.