Subsequent Events (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended									1 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 2026 Notes [Member]		Dec. 31, 2009 2026 Notes [Member]	Dec. 31, 2008 2026 Notes [Member]	Sep. 30, 2012 2026 Notes [Member]		Jan. 31, 2013 2026 Notes [Member] Subsequent Event [Member]
Subsequent Event [Line Items]
Stated Interest Rate				3.95%	[1],[2],[3]			(3.95%)	[1],[2],[3]
Debt converted				$ 123,163	[1],[2],[3]
Outstanding principal balance	238,572	361,735		15,537	[1],[2],[3],[4]
Repayment of notes payable - convertible	$ 164,649	$ 0	$ 0	$ (164,649)	[1],[2],[3]	$ 6,994	$ 19,188			$ 20,702

[1] 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.

[2] 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.

[3] 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.

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