Summary of Significant Accounting Policies - Revenue Recognition (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disaggregation of Revenue [Line Items]
Other operating	$ 2,068	$ 1,934	$ 3,963	$ 3,869
Parking Income
Disaggregation of Revenue [Line Items]
Other operating	1,819	1,669	3,445	3,238
Rental Lease Guaranty
Disaggregation of Revenue [Line Items]
Other operating	146	153	321	377
Management Fee Income
Disaggregation of Revenue [Line Items]
Other operating	69	68	137	167
Miscellaneous
Disaggregation of Revenue [Line Items]
Other operating	$ 34	$ 44	$ 60	$ 87