Schedule IV - Mortgage Loans on Real Estate (Details) (USD $)	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Mortgage Loans On Real Estate [Line Items]
Face Amount of Mortgages	$ 22,949,000
Carrying Amount of Mortgages	17,482,000	[1],[2]
Principal Amount of Loans Subject to Delinquent Principal or Interest	0
Movement in Mortgage Loans on Real Estate [Roll Forward]
Balance at beginning of year	22,815,000		21,138,000		34,707,000
New mortgage loans	7,344,000	[3]	8,098,000	[3]	6,302,000	[3]
Collections of principal	(12,339,000)		(6,421,000)		(7,148,000)
Foreclosures	(338,000)		0		(12,723,000)
Balance at the close of year	17,482,000		22,815,000		21,138,000
Mortgages held for federal income tax purposes	17,482,000		22,815,000		21,138,000
Payments to acquire mortgage notes receivable	7,344,000		8,098,000		6,302,000
Paramus, NJ [Member]
Mortgage Loans On Real Estate [Line Items]
Interest Rate	9.00%
Maturity Date	Feb. 01, 2022
Prior Liens	0
Face Amount of Mortgages	6,000,000
Carrying Amount of Mortgages	4,404,000	[1]
Principal Amount of Loans Subject to Delinquent Principal or Interest	0
Des Moines, IA [Member]
Mortgage Loans On Real Estate [Line Items]
Interest Rate	8.00%
Maturity Date	Oct. 15, 2013
Prior Liens	0
Face Amount of Mortgages	400,000
Carrying Amount of Mortgages	212,000	[1]
Principal Amount of Loans Subject to Delinquent Principal or Interest	0
Cleveland, OH [Member]
Mortgage Loans On Real Estate [Line Items]
Interest Rate	10.00%
Maturity Date	Oct. 01, 2028
Prior Liens	0
Face Amount of Mortgages	6,644,000
Carrying Amount of Mortgages	3,411,000	[1]
Principal Amount of Loans Subject to Delinquent Principal or Interest	0
Milford, CT [Member]
Mortgage Loans On Real Estate [Line Items]
Interest Rate	6.00%
Maturity Date	Jun. 30, 2016
Prior Liens	0
Face Amount of Mortgages	1,550,000
Carrying Amount of Mortgages	1,550,000	[1]
Principal Amount of Loans Subject to Delinquent Principal or Interest	0
Hollywood, FL [Member]
Mortgage Loans On Real Estate [Line Items]
Interest Rate	6.00%
Maturity Date	Apr. 28, 2013
Prior Liens	0
Face Amount of Mortgages	450,000
Carrying Amount of Mortgages	200,000	[1]
Principal Amount of Loans Subject to Delinquent Principal or Interest	0
Somerset, PA [Member]
Mortgage Loans On Real Estate [Line Items]
Interest Rate	9.50%
Maturity Date	Nov. 19, 2013
Prior Liens	0
Face Amount of Mortgages	1,179,000
Carrying Amount of Mortgages	1,179,000	[1]
Principal Amount of Loans Subject to Delinquent Principal or Interest	0
Spotsylvania, VA [Member]
Mortgage Loans On Real Estate [Line Items]
Interest Rate	9.50%
Maturity Date	Nov. 19, 2013
Prior Liens	0
Face Amount of Mortgages	1,226,000
Carrying Amount of Mortgages	1,226,000	[1]
Principal Amount of Loans Subject to Delinquent Principal or Interest	0
4 properties in FL and GA [Member]
Mortgage Loans On Real Estate [Line Items]
Interest Rate	6.25%
Maturity Date	Jan. 04, 2014
Prior Liens	0
Face Amount of Mortgages	5,500,000
Carrying Amount of Mortgages	5,300,000	[1]
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0

[1] Mortgages held by NNN and its subsidiaries for federal income tax purposes for the years ended December 31, 2012, 2011 and 2010 were $17,482, $22,815 and $21,138, respectively.

[2] The following shows the changes in the carrying amounts of mortgage loans during the years: 2012 2011 2010 Balance at beginning of year$22,815 $21,138 $34,707 New mortgage loans7,344 (h) 8,098 (h) 6,302 (h) Deductions during the year: Collections of principal(12,339) (6,421) (7,148) Foreclosures(338) — (12,723) Balance at the close of year$17,482 $22,815 $21,138

[3] Mortgages totaling $7,344, $8,098 and $6,302, were accepted in connection with real estate transactions for the years ended December 31, 2012, 2011 and 2010, respectively.