Organization and Summary of Significant Accounting Policies (Summary of NNN's Investment Portfolio) (Details) ft² in Thousands	9 Months Ended
	Sep. 30, 2018 ft² state property
Property Portfolio:
Total properties | property	2,847
Gross leasable area (square feet) | ft²	29,739
States | state	48
Weighted average remaining lease term (years)	11 years 5 months