Quarterly Financial Data (unaudited) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Revenues									$ 103,992		$ 100,776		$ 96,294		$ 92,465		$ 434,847	$ 393,525	$ 332,646
Net earnings attributable to NNN	53,757		47,940		45,571		43,333		44,241		44,352		37,486		34,066		190,601	160,145	142,015
Basic (in dollars per share)	$ 0.35	[1]	$ 0.31	[1]	$ 0.30	[1]	$ 0.28	[1]	$ 0.29	[1]	$ 0.29	[1]	$ 0.28	[1]	$ 0.26	[1]	$ 1.24	$ 1.11	$ 1.13
Diluted (in dollars per share)	$ 0.35	[1]	$ 0.31	[1]	$ 0.30	[1]	$ 0.28	[1]	$ 0.29	[1]	$ 0.29	[1]	$ 0.27	[1]	$ 0.25	[1]	$ 1.24	$ 1.10	$ 1.11
Revenues as originally reported (1)
Segment Reporting Information [Line Items]
Revenues	115,315	[2]	109,856	[2]	105,613	[2]	104,064	[2]	103,648		100,621		96,121		92,565
Reclassified to discontinued operations
Segment Reporting Information [Line Items]
Revenues									$ 344		$ 155		$ 173		$ (100)

[1] Calculated independently for each period and consequently, the sum of the quarters may differ from the annual amount.

[2] No revenues were reclassified to discontinued operations.