Organization and Summary of Significant Accounting Policies (Summary of NNN's Investment Portfolio) (Details) ft² in Thousands	9 Months Ended
	Sep. 30, 2020 ft² property state
Property Portfolio:
Total properties | property	3,114
Gross leasable area (square feet) | ft²	32,421
States | state	48
Weighted average remaining lease term	10 years 8 months 12 days