Quarterly Financial Data (unaudited) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended										12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011		Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010		Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Segment Reporting Information [Line Items]
Revenues	$ (74,400)	$ (67,643)	$ (62,059)	$ (61,691)		$ (59,516)	$ (56,303)	$ (56,021)	$ (56,049)		$ (265,793)	$ (227,888)	$ (228,827)
Net earnings attributable to NNN	27,570	22,632	21,303	20,820		14,215	21,210	21,207	16,365		92,325	72,997	54,810
Earnings Per Share, Basic	$ 0.26	$ 0.24	$ 0.23	$ 0.23	[1]	$ 0.15	$ 0.23	$ 0.23	$ 0.18	[1]	$ 0.96	$ 0.80	$ 0.60
Earnings Per Share, Diluted	$ 0.26	$ 0.24	$ 0.23	$ 0.23	[1]	$ 0.15	$ 0.23	$ 0.23	$ 0.18	[1]	$ 0.96	$ 0.80	$ 0.60
Revenues as originally reported [Member]
Segment Reporting Information [Line Items]
Revenues	(74,400)	(67,460)	(62,516)	(61,952)		(59,440)	(56,656)	(56,496)	(56,626)
Revenues reclassified to discontinued operations [Member]
Segment Reporting Information [Line Items]
Revenues	$ 0	$ 183	$ (457)	$ (261)		$ 76	$ (353)	$ (475)	$ (577)

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