Indebtedness - Summary of Indebtedness at Estimated Fair Value (Details) - USD ($) $ in Thousands		Sep. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Mortgage Loans Payable, Net		$ 305,018	$ 467,303
Senior Unsecured Notes, Net		540,952	269,731
Unsecured Term Loans		461,426	460,000
Unsecured Credit Facility		0	144,500
Total		1,307,396	1,341,534
Carrying Amount (A)
Debt Instrument [Line Items]
Mortgage Loans Payable, Net	[1]	299,605	451,862
Senior Unsecured Notes, Net	[1]	548,492	248,487
Unsecured Term Loans	[1]	460,000	460,000
Unsecured Credit Facility	[1]	0	144,500
Total	[1]	$ 1,308,097	$ 1,304,849

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