Revenue Recognition - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Property rentals									$ 152,795	$ 152,857	$ 151,444
Expense reimbursements									80,030	77,717	75,492
Total revenues	$ 57,567	$ 59,125	$ 58,253	$ 57,880	$ 58,061	$ 58,094	$ 57,190	$ 57,229	232,825	230,574	226,936
Base rent
Disaggregation of Revenue [Line Items]
Property rentals									146,881	146,833	145,293
Percentage rent
Disaggregation of Revenue [Line Items]
Property rentals									234	174	182
Parking revenue
Disaggregation of Revenue [Line Items]
Property rentals									5,680	5,850	5,969
Operating expense reimbursements
Disaggregation of Revenue [Line Items]
Expense reimbursements									76,273	73,757	71,699
Tenant services
Disaggregation of Revenue [Line Items]
Expense reimbursements									$ 3,757	$ 3,960	$ 3,793