Real Estate (Commitments) (Details) $ in Thousands	Dec. 31, 2017 USD ($) property
Real Estate [Abstract]
Number of properties \| property	27
Total commitment	$ 129,925
Amount funded	67,719
Remaining commitment	$ 62,206

Real Estate Investment, Funding Commitments, Remaining Commitment

No definition available.

Name:	nnn_RealEstateInvestmentFundingCommitmentsRemainingCommitment
Namespace Prefix:	nnn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant