Real Estate (Impairments) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Real Estate [Abstract]
Continuing operations	$ 1,028	$ 396
Discontinued operations	0	63
Impairment Losses and Other Charges	$ 1,028nnn_ImpairmentLossesAndOtherCharges	$ 459nnn_ImpairmentLossesAndOtherCharges

Impairment Losses, Continuing Operations, Net of Recoveries

No definition available.

Name:	nnn_ImpairmentLossesContinuingOperationsNetofRecoveries
Namespace Prefix:	nnn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration