Income Taxes (Income Tax Benefit (Expense)) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Net earnings before income taxes									$ 208,511	$ 190,844	$ 161,230
Current:
Federal									(58)	(190)	(195)
State and local									(129)	5	(90)
Deferred:
Federal									(8,935)	(166)	(790)
State and local									(1,553)	108	(10)
Total expense for income taxes									(10,675)	(243)	(1,085)
Net earnings attributable to NNN	$ 42,471	$ 55,198	$ 46,188	$ 53,978	$ 53,757	$ 47,940	$ 45,571	$ 43,333	$ 197,836	$ 190,601	$ 160,145