CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) - USD ($)	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement of Cash Flows [Abstract]
Restricted cash or cash held in escrow	$ 0	$ 0	$ 0

Restricted Cash and Investments, Restricted Cash and Cash Held in Escrow, Current

No definition available.

Name:	nnn_RestrictedCashandInvestmentsRestrictedCashandCashHeldinEscrowCurrent
Namespace Prefix:	nnn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant