Income Taxes (Income Tax Benefit (Expense)) (Details) (USD $) In Thousands, 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
Income Tax Disclosure [Abstract]
Net earnings before income taxes									$ 190,844	$ 161,230	$ 135,124
Current:
Federal									(190)	(195)	(136)
State and local									5	(90)	(7)
Deferred:
Federal									(166)	(790)	5,871
State and local									108	(10)	1,163
Total benefit (expense) for income taxes									(243)	(1,085)	6,891
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