Fair Value of Financial Instruments - Financial Instruments for which Estimates of Fair Value Differ from Carrying Amounts (Details) - USD ($) $ in Thousands		Mar. 31, 2018	Dec. 31, 2017
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Mortgage notes payable, net		$ 325,974	$ 317,216
Carrying Amount [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Note receivable	[1]	3,490	3,532
Carrying Amount [Member] | Unsecured Notes Payable [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Unsecured notes payable	[1]	1,286,936	1,286,573
Carrying Amount [Member] | Variable Rate Debt [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Variable rate debt	[1]	327,122	327,039
Carrying Amount [Member] | Mortgages Notes Payable [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Mortgage notes payable, net	[1]	325,974	317,216
Fair Value [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Note receivable, fair value		3,565	3,605
Fair Value [Member] | Unsecured Notes Payable [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Debt instrument, fair value		1,284,180	1,314,900
Fair Value [Member] | Variable Rate Debt [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Debt instrument, fair value		309,577	308,872
Fair Value [Member] | Mortgages Notes Payable [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Debt instrument, fair value		$ 312,402	$ 304,665

[1] In April 2015, the FASB issued guidance requiring that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct reduction from the carrying amount of the corresponding debt liability, consistent with debt discounts. As a result, the carrying amounts presented in the table above are net of deferred financing costs of $8.7 million and $8.9 million for unsecured notes payable, $1.5 million and $1.6 million for variable rate debt and $0.5 million and $0.6 million for mortgage notes payable as of March 31, 2018 and December 31, 2017, respectively.