Summary of Significant Accounting Policies - Revenue Recognition (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disaggregation of Revenue [Line Items]
Type of Revenue	$ 1,332	$ 1,966	$ 3,496	$ 3,928
Parking income
Disaggregation of Revenue [Line Items]
Type of Revenue	1,227	1,870	3,278	3,603
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	69	64	147	133
Miscellaneous
Disaggregation of Revenue [Line Items]
Type of Revenue	$ 36	$ 32	$ 71	$ 64