Schedule IV - Mortgage Loans on Real Estate (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018		Dec. 31, 2017
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest Rate		10.25%		10.00%
Prior Liens						$ 0
Face Amount of Mortgages						30,429
Carrying Amount of Mortgages		$ 30,429		$ 29,904	$ 41,618	30,429	[1]	$ 30,429
Principal Amount of Loans Subject to delinquent Principal or Interest						0
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate, Other Disclosure [Abstract]
Aggregate tax basis for Federal tax purposes						30,400		$ 30,400
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Balance at beginning of year		30,429		29,904	41,618
Collection and satisfaction of loans					(11,714)
Issuance of loans				525
Balance at end of year		30,429	[1]	$ 30,429	$ 29,904
Mortgage On Retail Buildings in Philadelphia, PA, Loan One
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior Liens						0
Face Amount of Mortgages						21,179
Carrying Amount of Mortgages	[2]	21,179				21,179
Principal Amount of Loans Subject to delinquent Principal or Interest						0
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Balance at end of year	[2]	$ 21,179
Mortgage On Retail Buildings in Philadelphia, PA, Loan One | Maximum
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Face Amount of Mortgages						25,000
Mortgage On Retail Buildings in Philadelphia, PA, Loan Two
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest Rate		10.00%
Prior Liens						0
Face Amount of Mortgages						9,250
Carrying Amount of Mortgages		$ 9,250				9,250
Principal Amount of Loans Subject to delinquent Principal or Interest						$ 0
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Balance at end of year		$ 9,250
Interest Rate One | Mortgage On Retail Buildings in Philadelphia, PA, Loan One
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest Rate		8.00%
Interest Rate Two | Mortgage On Retail Buildings in Philadelphia, PA, Loan One
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest Rate		10.00%

[1] For Federal tax purposes, the aggregate tax basis is approximately $30.4 million as of December 31, 2018.

[2] This mortgage is available for up to $25.0 million.