Indebtedness - Summary of Indebtedness at Estimated Fair Value (Details) - USD ($) $ in Thousands		Mar. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Carrying Amount	[1]	$ 1,411,794	$ 1,304,849
Fair Value		1,422,148	1,341,534
Mortgage Loans Payable
Debt Instrument [Line Items]
Carrying Amount	[1]	303,305	451,862
Fair Value		313,953	467,303
Senior Unsecured Notes
Debt Instrument [Line Items]
Carrying Amount	[1]	548,489	248,487
Fair Value		548,195	269,731
Unsecured Term Loan
Debt Instrument [Line Items]
Carrying Amount	[1]	460,000	460,000
Fair Value		460,000	460,000
Unsecured Credit Facility
Debt Instrument [Line Items]
Carrying Amount	[1]	100,000	144,500
Fair Value		$ 100,000	$ 144,500

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