Fair Value Measurements - Fair Value Disclosures (Details) $ in Thousands	Jun. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgages payable, net	$ 274,267	$ 287,068
Unsecured notes payable, net	696,055	695,748
Unsecured term loans, net	447,583	547,270
Unsecured revolving line of credit	126,000	216,000
Fair Value, Level 1
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Unsecured notes payable, net	234,853	243,183
Fair Value, Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgages payable, net	279,680	298,635
Unsecured notes payable, net	435,189	450,640
Unsecured term loans, net	455,242	552,555
Unsecured revolving line of credit	126,000	216,222
Fair Value, Total
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgages payable, net	279,680	298,635
Unsecured notes payable, net	670,042	693,823
Unsecured term loans, net	455,242	552,555
Unsecured revolving line of credit	126,000	216,222
Unsecured notes payable
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Unsecured notes payable, net	$ 700,000	$ 700,000
Discount rate | Unsecured revolving line of credit
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Input for measuring debt	0.0105	0.0130
Minimum | Discount rate | Mortgages payable
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Input for measuring debt	0.039	0.035
Maximum | Discount rate | Mortgages payable
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Input for measuring debt	0.045	0.042
Weighted average | Discount rate | Unsecured term loans
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Input for measuring debt	0.0120	0.0133
Notes Due 2021, 2024, 2026 and 2028 | Weighted average | Discount rate | Unsecured notes payable
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Input for measuring debt	0.0490	0.0428