Organization and Summary of Significant Accounting Policies (Summary of NNN's Investment Portfolio) (Details) ft² in Thousands	12 Months Ended
	Dec. 31, 2018 ft² state property
Property Portfolio:
Total properties | property	2,969
Gross leasable area (square feet) | ft²	30,487
States | state	48
Weighted average remaining lease term (years)	11 years 6 months