Income Taxes (Income Tax Benefit (Expense)) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Tax Disclosure [Abstract]
Net earnings before income taxes									$ 161,230	$ 135,124	$ 93,302
Federal									(195)	(136)	(166)
State and local									(90)	(7)	(15)
Federal									(790)	5,871	(714)
State and local									(10)	1,163	(82)
Total benefit (expense) for income taxes									(1,085)	6,891	(977)
Net earnings attributable to NNN	$ 44,241	$ 40,663	$ 44,352	$ 37,486	$ 34,066	$ 38,015	$ 33,505	$ 29,832	$ 160,145	$ 142,015	$ 92,325