Segment Information - Revenue (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021 USD ($) property	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) property	Sep. 30, 2020 USD ($)
Segment revenue information
Rental (including reimbursable)	$ 486,337	$ 401,869	$ 1,385,958	$ 1,224,227
Other	5,538	2,703	13,003	9,322
Total revenue	$ 491,875	404,572	$ 1,398,961	1,233,549
Number of properties owned | property	7,018		7,018
Automotive service
Segment revenue information
Rental (including reimbursable)	$ 10,992	8,763	$ 31,144	26,094
Beverages
Segment revenue information
Rental (including reimbursable)	9,453	8,071	27,784	24,062
Child care
Segment revenue information
Rental (including reimbursable)	8,872	8,710	26,186	26,959
Convenience stores
Segment revenue information
Rental (including reimbursable)	53,649	47,807	154,865	141,310
Dollar stores
Segment revenue information
Rental (including reimbursable)	35,085	31,710	100,439	94,696
Drug stores
Segment revenue information
Rental (including reimbursable)	34,790	35,043	106,194	105,959
Financial services
Segment revenue information
Rental (including reimbursable)	7,588	7,583	22,905	22,700
General merchandise
Segment revenue information
Rental (including reimbursable)	17,539	12,937	49,625	36,341
Grocery stores - U.S.
Segment revenue information
Rental (including reimbursable)	20,018	19,451	59,279	58,444
Grocery stores - U.K.
Segment revenue information
Rental (including reimbursable)	26,764	12,858	71,404	35,001
Health and fitness
Segment revenue information
Rental (including reimbursable)	27,741	25,905	83,459	82,145
Home improvement - U.S.
Segment revenue information
Rental (including reimbursable)	14,776	11,373	41,358	34,065
Home improvement - U.K.
Segment revenue information
Rental (including reimbursable)	10,294	448	21,442	448
Restaurants-casual dining
Segment revenue information
Rental (including reimbursable)	12,706	11,731	36,432	35,699
Restaurants-quick service - U.S.
Segment revenue information
Rental (including reimbursable)	26,362	23,047	74,033	65,224
Theaters - U.S.
Segment revenue information
Rental (including reimbursable)	25,771	12,781	64,966	61,795
Transportation services
Segment revenue information
Rental (including reimbursable)	17,281	15,981	50,540	47,941
Wholesale club
Segment revenue information
Rental (including reimbursable)	10,683	9,611	30,773	28,788
Other non-reportable segments and tenant reimbursements
Segment revenue information
Rental (including reimbursable)	$ 115,973	$ 98,059	$ 333,130	$ 296,556
Spain
Segment revenue information
Number of properties owned | property	7		7