Segment Information - Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment revenue information
Rental (including reimbursable)	$ 401,869	$ 372,312	$ 1,224,227	$ 1,090,601
Other	2,703	1,935	9,322	3,461
Total revenue	404,572	374,247	1,233,549	1,094,062
Automotive service
Segment revenue information
Rental (including reimbursable)	8,763	8,505	26,094	23,735
Automotive tire services
Segment revenue information
Rental (including reimbursable)	7,847	7,766	23,795	23,517
Beverages
Segment revenue information
Rental (including reimbursable)	8,071	7,988	24,062	23,819
Child care
Segment revenue information
Rental (including reimbursable)	8,710	7,837	26,959	23,425
Convenience stores
Segment revenue information
Rental (including reimbursable)	47,807	41,286	141,310	123,932
Dollar stores
Segment revenue information
Rental (including reimbursable)	31,710	25,213	94,696	75,311
Drug stores
Segment revenue information
Rental (including reimbursable)	35,043	31,902	105,959	97,414
Financial services
Segment revenue information
Rental (including reimbursable)	7,583	7,585	22,700	22,997
General merchandise
Segment revenue information
Rental (including reimbursable)	12,937	9,594	36,341	25,115
Grocery stores - U.S.
Segment revenue information
Rental (including reimbursable)	19,451	17,673	58,444	51,009
Grocery stores - U.K.
Segment revenue information
Rental (including reimbursable)	12,858	6,618	35,001	9,533
Health and fitness
Segment revenue information
Rental (including reimbursable)	25,905	26,437	82,145	78,915
Home improvement - U.S.
Segment revenue information
Rental (including reimbursable)	11,373	10,950	34,065	31,430
Restaurants-casual dining
Segment revenue information
Rental (including reimbursable)	11,731	10,939	35,699	33,614
Restaurants-quick service
Segment revenue information
Rental (including reimbursable)	23,047	21,880	65,224	65,124
Theaters - U.S.
Segment revenue information
Rental (including reimbursable)	12,781	24,002	61,795	62,567
Transportation services
Segment revenue information
Rental (including reimbursable)	15,981	16,109	47,941	48,327
Wholesale club
Segment revenue information
Rental (including reimbursable)	9,611	9,468	28,788	28,525
Other non-reportable segments and tenant reimbursements
Segment revenue information
Rental (including reimbursable)	$ 90,660	$ 80,560	$ 273,209	$ 242,292