CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) - USD ($)	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Cash Flows [Abstract]
Restricted cash or cash held in escrow	$ 0	$ 0	$ 601,000

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