Real Estate Properties - Additional Information (Details) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2019 USD ($) ft² lease property	Jun. 30, 2019 USD ($) ft² lease property joint_venture	Dec. 31, 2018 USD ($)
Real Estate Properties [Line Items]
Real estate properties at aggregate cost	$ 3,816,394	$ 3,816,394	$ 3,944,636
Number of joint ventures | joint_venture		2
Number of leases entered | lease	24	56
Rentable square feet (in sqft) | ft²	570,757	1,396,232
Weighted average lease term	6 years 8 months	7 years 2 months
Expenditures committed on leases	$ 15,377	$ 44,181
Committed but unspent tenant related obligations estimated	$ 61,283	$ 61,283
Continuing operations
Real Estate Properties [Line Items]
Number of properties | property	209	209
Rentable area of properties (in square feet) | ft²	29,309,000	29,309,000
Real estate properties at aggregate cost	$ 3,929,413	$ 3,929,413
Unconsolidated Joint Ventures
Real Estate Properties [Line Items]
Number of properties | property	3	3
Rentable area of properties (in square feet) | ft²	443,867	443,867
Number of buildings, noncontrolling interest | property		3
Joint Venture 1
Real Estate Properties [Line Items]
Equity Method Investment, Ownership Percentage	50.00%	50.00%
Joint Venture 2
Real Estate Properties [Line Items]
Equity Method Investment, Ownership Percentage	51.00%	51.00%
Held-for-sale
Real Estate Properties [Line Items]
Number of properties | property	9	9
Rentable area of properties (in square feet) | ft²	1,686,365	1,686,365
Real estate held for sale	$ 113,019	$ 113,019