Noncontrolling Interests - Narrative (Details) $ in Thousands	1 Months Ended			9 Months Ended		12 Months Ended
	Jul. 31, 2019 USD ($)	Jan. 31, 2019 USD ($) shares	Dec. 31, 2018 entity	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2016 property entity
Noncontrolling interests
Conversion ratio				1
Number of properties acquired | property						2
Number of joint ventures controlling interest acquired | entity						2
Number of entities in which all outstanding minority interests were acquired | entity			1
Redemption of partnership units				$ 21,123	$ 0
Term Loans | $70 million senior unsecured term loan
Noncontrolling interests
Repayments of long-term debt		$ 70,000
Tau Operating Partnership
Noncontrolling interests
Number of partnership units redeemed (in units) | shares		317,022
Ownership interest (as a percent)		100.00%
Third-party partnership ownership interest (as a percent)		0.11%
Redemption of partnership units		$ 20,200
Excess of redemption of units over carrying value as reduction to common stock and paid in capital		$ 6,900
Realty Income, L.P.
Noncontrolling interests
Ownership interest (as a percent)				98.10%
Third-party partnership ownership interest (as a percent)				1.90%
Other Noncontrolling Interest One
Noncontrolling interests
Redemption of partnership units	$ 900