Indebtedness - Summary of Indebtedness at Estimated Fair Value (Details) - USD ($) $ in Thousands		Sep. 30, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Carrying Amount	[1]	$ 1,375,050	$ 1,353,679
Fair Value		1,417,784	1,384,111
Mortgage Loans Payable
Debt Instrument [Line Items]
Carrying Amount	[1]	454,584	498,861
Fair Value		466,999	513,540
Senior Unsecured Notes
Debt Instrument [Line Items]
Carrying Amount	[1]	303,466	205,318
Fair Value		325,580	222,469
Unsecured Term Loan
Debt Instrument [Line Items]
Carrying Amount	[1]	460,000	460,000
Fair Value		468,089	458,602
Unsecured Credit Facility
Debt Instrument [Line Items]
Carrying Amount	[1]	157,000	189,500
Fair Value		$ 157,116	$ 189,500

[1] The carrying amounts include unamortized premiums and discounts and exclude unamortized deferred financing costs.