Leases - Tenant Accounts Receivable (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) leases	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Cash Basis Leases | leases			11
Accrued Rent Adjustment To Rental Income Resulting From Lease Collectibility Assessment	$ 800,000	$ 0	$ 1,700,000	$ 0
Contractual Rent Adjustment To Rental Income Resulting From Lease Collectibility Assessment	900,000	0	1,500,000	0
Lease Security Deposits Available in Letters of Credit	28,400,000		28,400,000		$ 22,600,000
Lease security deposits in restricted cash	700,000		700,000		700,000
Lease security deposits included in tenant prepaid rent and security deposits on the Balance Sheet	10,100,000		10,100,000		9,800,000
Real Estate Taxes, Tenant Responsibility	5,000,000.0	$ 5,100,000	14,700,000	$ 13,100,000
Accrued Income Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Deferred Rent Receivables, Net	$ 54,600,000		$ 54,600,000		$ 44,300,000