Segment Information - Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Segment revenue information
Rental (including reimbursable)	$ 354,037	$ 317,848
Other	328	447
Total revenue	354,365	318,295
Automotive service
Segment revenue information
Rental (including reimbursable)	7,213	7,009
Automotive tire services
Segment revenue information
Rental (including reimbursable)	7,777	7,439
Beverages
Segment revenue information
Rental (including reimbursable)	7,915	7,836
Child care
Segment revenue information
Rental (including reimbursable)	7,827	5,672
Convenience stores
Segment revenue information
Rental (including reimbursable)	41,214	28,000
Dollar stores
Segment revenue information
Rental (including reimbursable)	24,986	23,250
Drug stores
Segment revenue information
Rental (including reimbursable)	33,170	32,242
Financial services
Segment revenue information
Rental (including reimbursable)	7,718	7,020
General merchandise
Segment revenue information
Rental (including reimbursable)	6,911	6,870
Grocery stores
Segment revenue information
Rental (including reimbursable)	16,124	15,665
Health and fitness
Segment revenue information
Rental (including reimbursable)	26,225	23,444
Home improvement
Segment revenue information
Rental (including reimbursable)	9,815	9,244
Motor vehicle dealerships
Segment revenue information
Rental (including reimbursable)	7,348	7,311
Restaurants-casual dining
Segment revenue information
Rental (including reimbursable)	11,290	10,948
Restaurants-quick service
Segment revenue information
Rental (including reimbursable)	21,730	16,249
Theaters
Segment revenue information
Rental (including reimbursable)	17,656	17,770
Transportation services
Segment revenue information
Rental (including reimbursable)	16,026	15,786
Wholesale club
Segment revenue information
Rental (including reimbursable)	9,593	9,532
Other non-reportable segments and tenant reimbursements
Segment revenue information
Rental (including reimbursable)	$ 73,499	$ 66,561