Revenues - Summary of Revenues (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]
Rental income	$ 169,529	$ 158,187	$ 332,934	$ 313,577
Tenant reimbursement income	13,164	11,856	27,410	24,708
Fee income:
Total fee income	5,409	4,448	8,874	14,004
Lease termination income	29	895	57	961
Other income	3,288	2,318	6,415	5,690
Total fee and other income	8,726	7,661	15,346	20,655
Total revenues	191,419	177,704	375,690	358,940
Property Management Fees [Member]
Fee income:
Total fee income	1,490	1,532	2,992	3,142
Asset Management Fees [Member]
Fee income:
Total fee income	1,823	2,359	3,433	4,625
Acquisition, Disposition and Leasing Fee [Member]
Fee income:
Total fee income	1,750	250	1,750	5,570
Other Fee Income [Member]
Fee income:
Total fee income	$ 346	$ 307	$ 699	$ 667