Real Estate Properties - Additional Information (Details) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2018 USD ($) ft² lease property building	Sep. 30, 2018 USD ($) ft² lease property joint_venture building
Real Estate Properties [Line Items]
Number of Properties | property	105	105
Number of buildings | building	164	164
Number of joint ventures | joint_venture		2
Number of properties, noncontrolling interest | property		2
Number of buildings, noncontrolling interest | building		3
Number of leases entered | lease	24	94
Rentable square feet (in sqft) | ft²	182,220	858,998
Weighted average lease term	8 years 1 month	6 years 5 months
Expenditures committed on leases | $	$ 6,479	$ 21,287
Committed but unspent tenant related obligations estimated | $	$ 34,048	$ 34,048
Continuing operations
Real Estate Properties [Line Items]
Number of Properties | property	105	105
Number of buildings | building	164	164
Carry value of properties | $	$ 2,854,937	$ 2,854,937