Supplemental Disclosures of Cash Flow Information (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Apr. 30, 2018	Mar. 30, 2018	Dec. 31, 2017	Dec. 31, 2016	Jun. 27, 2013
Supplemental Disclosures of Cash Flow Information
Cash paid for interest	$ 197,200	$ 198,800
Cash paid for income taxes	4,000	4,000
Non-cash activities
Non-refundable escrow deposits for pending acquisitions	3,275				$ 7,500
Value of property acquired with funds previously held in escrow account	7,500
Reconciliation of cash and cash equivalents
Cash and cash equivalents shown in the consolidated balance sheets	6,666	3,199			6,898
Restricted escrow deposits	1,533	23,698			679
Impounds related to mortgages payable	7,529	3,465			4,565
Total cash, cash equivalents, and restricted cash shown in the consolidated statements of cash flows	15,728	30,362			$ 12,142	$ 15,681
Properties under development
Supplemental Disclosures of Cash Flow Information
Interest capitalized to properties under development	$ 234	$ 347
Realty Income, L.P.
Non-cash activities
Number of partnership units issued	373,797		131,790	242,007			534,546
Value of partnership units issued	$ 18,800