Notes Payable (Unsecured Senior Notes) (Details) - Unsecured Senior Notes	9 Months Ended
	Sep. 30, 2019 USD ($) tranche
Debt Instrument [Line Items]
Debt amount	$ 1,000,000,000.0
Number of tranches | tranche	5
Minimum fixed charge coverage ratio	1.50
Minimum
Debt Instrument [Line Items]
Minimum unencumbered interest coverage ratio	1.75
Maximum
Debt Instrument [Line Items]
Leverage ratio (percent)	60.00%
Secured leverage ratio (percent)	40.00%
4.09% Senior Notes, Unsecured
Debt Instrument [Line Items]
Debt amount	$ 100,000,000
Interest rate	4.09%
3.91% Senior Notes, Unsecured
Debt Instrument [Line Items]
Debt amount	$ 250,000,000
Interest rate	3.91%
3.78% Senior Notes, Unsecured
Debt Instrument [Line Items]
Debt amount	$ 125,000,000
Interest rate	3.78%
3.86% Senior Notes, Unsecured
Debt Instrument [Line Items]
Debt amount	$ 250,000,000
Interest rate	3.86%
3.95% Senior Notes, Unsecured
Debt Instrument [Line Items]
Debt amount	$ 275,000,000
Interest rate	3.95%