Notes Payable (Credit Facility) (Details) - Credit Facility		9 Months Ended
	Sep. 30, 2019 USD ($)	Sep. 30, 2019 USD ($)
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 1,000,000,000	$ 1,000,000,000
Minimum fixed charge coverage ratio		1.50
Available borrowing capacity	$ 920,000,000.0	$ 920,000,000.0
LIBOR
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)	1.05%
Federal Funds Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)		0.50%
One-month LIBOR
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)		1.00%
Minimum
Line of Credit Facility [Line Items]
Minimum unencumbered interest coverage ratio		1.75
Minimum | LIBOR
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)		1.05%
Minimum | Base Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)		0.10%
Maximum
Line of Credit Facility [Line Items]
Secured leverage ratio (percent)		40.00%
Leverage ratio (percent)	60.00%	60.00%
Maximum | LIBOR
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)		1.45%
Maximum | Base Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)		0.45%