Quarterly Financial Data (unaudited) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2012		Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2011		Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Segment Reporting Information [Line Items]
Revenues	$ 88,899		$ 84,327		$ 81,316		$ 77,210		$ 72,959		$ 66,166		$ 60,596		$ 60,218		$ 331,752	$ 259,939	$ 222,084
Net earnings attributable to NNN	40,663		38,015		33,505		29,832		27,570		22,632		21,303		20,820		142,015	92,325	72,997
Basic (in dollars per share)	$ 0.33	[1]	$ 0.31	[1]	$ 0.26	[1]	$ 0.23	[1]	$ 0.26	[1]	$ 0.24	[1]	$ 0.23	[1]	$ 0.23	[1]	$ 1.13	$ 0.96	$ 0.80
Diluted (in dollars per share)	$ 0.32	[1]	$ 0.30	[1]	$ 0.26	[1]	$ 0.23	[1]	$ 0.26	[1]	$ 0.24	[1]	$ 0.23	[1]	$ 0.23	[1]	$ 1.11	$ 0.96	$ 0.80
Revenues as originally reported [Member]
Segment Reporting Information [Line Items]
Revenues	88,899		85,013		82,751		78,658		74,400		67,460		62,516		61,952
Revenues reclassified to discontinued operations [Member]
Segment Reporting Information [Line Items]
Revenues	$ 0		$ 686		$ 1,435		$ 1,448		$ 1,441		$ 1,294		$ 1,920		$ 1,734

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