Summary of Significant Accounting Policies - Tenant Receivables and Deferred Rent Receivables (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Letters of credit from our tenants	$ 25,212	$ 25,535
Cash security deposits from our tenants	50,414	45,990
Tenant Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for doubtful accounts	3,062	2,656
Increase (decrease) in net income from change in receivable allowance	(406)	(422)	$ (223)
Deferred Rent Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for doubtful accounts	3,405	5,144
Increase (decrease) in net income from change in receivable allowance	$ 1,739	$ 898	$ (242)