Organization and Summary of Significant Accounting Policies (Summary of NNN's Investment Portfolio) (Details) ft² in Thousands	12 Months Ended
	Dec. 31, 2020 ft² property state
Property Portfolio:
Total properties | property	3,143
Gross leasable area (square feet) | ft²	32,461
States | state	48
Weighted average remaining lease term (years)	10 years 8 months 12 days