Debt - Schedule of Mortgages Payable (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Debt Instrument [Line Items]
Borrowings under mortgages payable	$ 41,344	$ 220,000
Mortgages payable
Debt Instrument [Line Items]
Repayment of mortgages payable	$ 162,500
Variable interest rate	3.94%
Fixed interest rate	4.15%
Variable rate amount	$ 266,615		$ 498,253
Fixed rate amount	1,644,111		1,537,706
Debt, gross	1,910,726		2,035,959
Unamortized deferred financing costs and premium/ discount, net	(4,324)		(10,267)
Debt, net	1,906,402		2,025,692
Derivative, notional amount	1,300,000		$ 1,400,000
Derivatives Entered Into, Notional Value	$ 374,200