Organization and Summary of Significant Accounting Policies (Summary of NNN's Investment Portfolio) (Details) ft² in Thousands	3 Months Ended
	Mar. 31, 2018 ft² state property
Property Portfolio:
Total properties | property	2,800
Gross leasable area (square feet) | ft²	29,116
States | state	48
Weighted average remaining lease term (years)	11 years 5 months