Notes Payable - Convertible (Details) (USD $)	12 Months Ended										12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 2026 Notes [Member]		Dec. 31, 2011 2026 Notes [Member]	Dec. 31, 2009 2026 Notes [Member]	Dec. 31, 2008 2026 Notes [Member]	Sep. 30, 2012 2026 Notes [Member]		Dec. 31, 2012 2028 Notes [Member]		Dec. 31, 2011 2028 Notes [Member]	Dec. 31, 2009 2028 Notes [Member]		Dec. 31, 2012 Convertible Debt [Member]	Dec. 31, 2011 Convertible Debt [Member]	Dec. 31, 2010 Convertible Debt [Member]	Nov. 06, 2012 Convertible Debt [Member]
Debt Instrument [Line Items]
Net Proceeds				$ 168,650,000	[1],[2],[3]						$ 228,576,000	[1],[4],[5]
Stated Interest Rate				3.95%	[1],[2],[3]				(3.95%)	[1],[2],[3]	5.125%	[1],[4],[5]
Effective Interest Rate				5.84%	[1],[2],[3],[6]						7.192%	[1],[4],[5],[6]
Debt Issuance Costs				3,850,000	[1],[2],[3],[7]						5,459,000	[1],[4],[5],[8]
Original Principal				172,500,000	[1],[2],[3]						234,035,000	[1],[4],[5]
Repurchases				(33,800,000)	[1],[2],[3]		(8,800,000)	(25,000,000)						(11,000,000)	[1],[4],[5]
Debt converted				(123,163,000)	[1],[2],[3]						0	[1],[4],[5]
Outstanding principal balance	238,572,000	361,735,000		15,537,000	[1],[2],[3],[9]						223,035,000	[1],[4],[5]							38,100,000
Repayment of notes payable - convertible	164,649,000	0	0	(164,649,000)	[1],[2],[3]		6,994,000	19,188,000						8,588,000
Gains on extinguishment of debt							1,565,000	4,961,000			1,867,000
Write off of deferred debt issuance cost				463,000							219,000
Conversion price				$ 23.4611							$ 25.3228
Conversion rate basis				1							1
Convertible notes payable, shares issued upon conversion				42.6237							39.4902
Effective interest rate				5.84%							7.192%
Carrying value of equity component	(22,193,000)	(33,873,000)
Remaining unamortized debt discount	(2,072,000)	(6,363,000)
Net carrying value of convertible debt	214,307,000	321,499,000
Remaining discount amortization period											6 years
Noncash interest charges																4,291,000	5,837,000	6,154,000
Contractual interest expense																15,744,000	16,909,000	17,046,000
Interest Expense, Debt																20,035,000	22,746,000	23,200,000
If-converted value in excess of principal				5,125,000		16,057,000					51,764,000		8,831,000
Equity component of convertible debt	$ 41,486,000			$ 41,486,000

[1] Debt issuance costs include underwriting discounts and commissions, legal and accounting fees, rating agency fees and printing expenses. These costs have been deferred and are being amortized over the period to the earliest put option date of the holders using the effective interest method.

[2] NNN repurchased $8,800 and $25,000 in 2009 and 2008, respectively, for a purchase price of $6,994 and $19,188, respectively, resulting in a gain of $1,565 and $4,961, respectively.

[3] The conversion rate per $1 principal amount was 42.6237 shares of NNN’s common stock, which is equivalent to a conversion price of $23.4611 per share of common stock.

[4] The conversion rate per $1 principal amount was 39.4902 shares of NNN’s common stock, which is equivalent to a conversion price of $25.3228 per share of common stock.

[5] NNN repurchased $11,000 in 2009 for a purchase price of $8,588 resulting in a gain of $1,867.

[6] With the adoption of the accounting guidance on convertible debt securities in 2009, the effective interest rates for the 2026 Notes and the 2028 Notes are 5.840% and 7.192%, respectively.

[7] Includes $463 of note costs which were written off in connection with the repurchase of $33,800 of the 2026 Notes.

[8] Includes $219 of note costs which were written off in connection with the repurchase of $11,000 of the 2028 Notes, respectively.

[9] In January 2013, NNN converted the remaining principal balance.