Noncontrolling Interests - Holders of Convertible Limited Partnership Units in the Operating Partnership (Details) - Noncontrolling Interests shares in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020 shares	Jun. 30, 2019 shares	Jun. 30, 2020 shares	Jun. 30, 2019 shares
Noncontrolling Interest [Line Items]
Limited partnership units (in shares)	7.9		7.9
Limited partnership units, conversion ratio	1		1
Outstanding stock percent that should be acquired for rights to be exercised	39.90%		39.90%
Limited partnership units convertible into shares of common stock, eligible for conversion (in shares)	1.8		1.8
Fully converted partnership units and diluted weighted average shares outstanding (in shares)	31.2	30.8	31.2	30.8
Saul Holdings Limited Partnership
Noncontrolling Interest [Line Items]
Percentage of ownership interest of noncontrolling interest	25.40%		25.40%