Segment Information - Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment revenue information
Revenue	$ 1,327,838	$ 1,215,768	$ 1,103,172
Rental
Segment revenue information
Revenue	1,274,596	1,166,224	1,057,413
Tenant reimbursements
Segment revenue information
Revenue	46,950	46,082	43,104
Other
Segment revenue information
Revenue	6,292	3,462	2,655
Apparel | Rental
Segment revenue information
Revenue	16,768	19,190	19,975
Automotive service | Rental
Segment revenue information
Revenue	28,303	25,291	20,212
Automotive tire services | Rental
Segment revenue information
Revenue	30,078	29,560	28,754
Beverages | Rental
Segment revenue information
Revenue	31,488	31,174	27,587
Convenience Stores | Rental
Segment revenue information
Revenue	142,194	111,023	91,784
Dollar stores | Rental
Segment revenue information
Revenue	94,782	91,076	90,746
Drug stores | Rental
Segment revenue information
Revenue	129,565	126,555	117,758
Financial services | Rental
Segment revenue information
Revenue	29,429	28,744	18,769
General merchandise | Rental
Segment revenue information
Revenue	29,249	23,752	18,976
Grocery stores | Rental
Segment revenue information
Revenue	63,594	50,731	32,815
Health and fitness | Rental
Segment revenue information
Revenue	94,638	88,146	85,901
Home improvement | Rental
Segment revenue information
Revenue	37,939	30,324	25,695
Motor vehicle dealerships | Rental
Segment revenue information
Revenue	24,372	23,989	20,329
Restaurants-casual dining | Rental
Segment revenue information
Revenue	46,171	43,876	42,312
Restaurants-quick service | Rental
Segment revenue information
Revenue	72,465	59,638	52,674
Theaters | Rental
Segment revenue information
Revenue	70,560	58,443	51,926
Transportation services | Rental
Segment revenue information
Revenue	63,565	62,337	57,694
Wholesale club | Rental
Segment revenue information
Revenue	37,571	37,646	37,531
Other non-reportable segments | Rental
Segment revenue information
Revenue	$ 231,865	$ 224,729	$ 215,975