Summary of Significant Accounting Policies - Revenue Recognition (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Type of Revenue	$ 1,868	$ 2,059	$ 5,364	$ 5,987
Parking income
Disaggregation of Revenue [Line Items]
Type of Revenue	1,764	1,935	5,042	5,538
Rental lease guaranty
Disaggregation of Revenue [Line Items]
Type of Revenue	0	0	0	128
Management fee income
Disaggregation of Revenue [Line Items]
Type of Revenue	62	69	209	201
Miscellaneous
Disaggregation of Revenue [Line Items]
Type of Revenue	$ 42	$ 55	$ 113	$ 120