Segment Information - Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Segment revenue information
Rental (including reimbursable)	$ 410,201	$ 364,252	$ 822,358	$ 718,289
Other	4,435	1,198	6,619	1,526
Total revenue	414,636	365,450	828,977	719,815
Automotive service
Segment revenue information
Rental (including reimbursable)	8,661	8,039	17,332	15,230
Automotive tire services
Segment revenue information
Rental (including reimbursable)	8,115	7,952	15,948	15,751
Beverages
Segment revenue information
Rental (including reimbursable)	7,996	7,915	15,991	15,831
Child care
Segment revenue information
Rental (including reimbursable)	8,714	7,760	18,195	15,587
Convenience stores
Segment revenue information
Rental (including reimbursable)	46,819	41,432	93,552	82,646
Dollar stores
Segment revenue information
Rental (including reimbursable)	31,595	25,112	62,986	50,098
Drug stores
Segment revenue information
Rental (including reimbursable)	35,617	32,343	70,916	65,513
Financial services
Segment revenue information
Rental (including reimbursable)	7,573	7,694	15,116	15,412
General merchandise
Segment revenue information
Rental (including reimbursable)	11,887	8,610	23,404	15,520
Grocery stores - U.S.
Segment revenue information
Rental (including reimbursable)	19,485	17,211	38,994	33,336
Grocery stores - U.K.
Segment revenue information
Rental (including reimbursable)	11,739	2,915	22,143	2,915
Health and fitness
Segment revenue information
Rental (including reimbursable)	27,961	26,254	56,239	52,479
Home improvement
Segment revenue information
Rental (including reimbursable)	11,382	10,664	22,692	20,479
Restaurants-casual dining
Segment revenue information
Rental (including reimbursable)	11,431	11,385	23,969	22,674
Restaurants-quick service
Segment revenue information
Rental (including reimbursable)	18,820	21,515	42,128	43,244
Theaters - U.S.
Segment revenue information
Rental (including reimbursable)	24,448	20,909	49,014	38,565
Transportation services
Segment revenue information
Rental (including reimbursable)	15,975	16,192	31,960	32,218
Wholesale club
Segment revenue information
Rental (including reimbursable)	9,588	9,464	19,176	19,057
Other non-reportable segments and tenant reimbursements
Segment revenue information
Rental (including reimbursable)	$ 92,395	$ 80,886	$ 182,603	$ 161,734