Summary of Significant Accounting Policies - Accounts Receivable and Accrued Rent Receivable (Textual) (Details) $ in Thousands	Dec. 31, 2017 USD ($) Customer	Dec. 31, 2016 USD ($) Customer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for Doubtful Accounts Receivable	$ 3,467	$ 2,373
Accrued rent receivable, allowance	13,645	13,743
Tenant Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for Doubtful Accounts Receivable	$ 3,500	$ 2,400
Accounts Receivable [Member] | Customer Concentration Risk [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of tenant accounted for 10% or more of the Company's accounts receivable | Customer	0	0