Indebtedness - Summary of Indebtedness at Estimated Fair Value (Details) - USD ($) $ in Thousands		Sep. 30, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Mortgage Loans Payable, Net		$ 193,453	$ 304,508
Senior Unsecured Notes, Net		760,282	546,607
Unsecured Term Loans		461,005	461,317
Unsecured Credit Facility		78,079	0
Total		1,492,819	1,312,432
Carrying Amount (A)
Debt Instrument [Line Items]
Mortgage Loans Payable, Net	[1]	181,092	297,716
Senior Unsecured Notes, Net	[1]	698,498	548,494
Unsecured Term Loans	[1]	460,000	460,000
Unsecured Credit Facility	[1]	78,000	0
Total	[1]	$ 1,417,590	$ 1,306,210

[1] The carrying amounts include unamortized premiums and discounts and exclude unamortized debt issuance costs.