Revenue Recognition - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Property rentals	$ 38,250	$ 37,970	$ 115,109	$ 114,507
Expense reimbursements	20,875	20,124	60,149	58,006
Base rent
Disaggregation of Revenue [Line Items]
Property rentals	36,844	36,584	110,754	109,997
Percentage rent
Disaggregation of Revenue [Line Items]
Property rentals	0	11	234	174
Parking revenue
Disaggregation of Revenue [Line Items]
Property rentals	1,406	1,375	4,121	4,336
Operating expense reimbursements
Disaggregation of Revenue [Line Items]
Expense reimbursements	19,995	19,029	57,371	54,879
Tenant services
Disaggregation of Revenue [Line Items]
Expense reimbursements	880	1,095	2,778	3,127
Real Estate
Disaggregation of Revenue [Line Items]
Total revenues	$ 59,125	$ 58,094	$ 175,258	$ 172,513