Real Estate (Commitments) (Details) $ in Thousands	Dec. 31, 2018 USD ($) property
Real Estate [Abstract]
Number of properties \| property	19
Total commitment	$ 34,756
Less amount funded	13,588
Remaining commitment	$ 21,168

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