Revenues - Summary of Revenues (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]
Rental income	$ 167,934	$ 156,384	$ 500,868	$ 469,961
Tenant reimbursement income	15,579	14,053	42,989	38,761
Fee income:
Total fee income	4,079	5,834	12,953	19,838
Lease termination income	1,561	954	1,618	1,915
Other income	3,443	2,545	9,858	8,235
Total fee and other income	9,083	9,333	24,429	29,988
Total revenues	192,596	179,770	568,286	538,710
Property Management Fees [Member]
Fee income:
Total fee income	1,476	1,673	4,468	4,815
Asset Management Fees [Member]
Fee income:
Total fee income	2,222	1,997	5,655	6,622
Acquisition, Disposition and Leasing Fee [Member]
Fee income:
Total fee income		1,475	1,750	7,045
Other Fee Income [Member]
Fee income:
Total fee income	$ 381	$ 689	$ 1,080	$ 1,356