Organization and Summary of Significant Accounting Policies (Computation of Basic and Diluted Earnings Per Share) (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Oct. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Basic and Diluted Earnings:
Net earnings attributable to NNN		$ 228,799	$ 299,180	$ 292,447
Less: Excess of redemption value over carrying value of preferred shares redeemed		0	(9,856)	0
Net earnings available to common stockholders		210,859	258,183	258,120
Less: Earnings allocated to unvested restricted shares		(698)	(601)	(548)
Net earnings used in basic and diluted earnings per share		$ 210,161	$ 257,582	$ 257,572
Basic and Diluted Weighted Average Shares Outstanding:
Weighted average number of shares outstanding (in shares)		172,994,337	165,499,707	156,490,901
Less: Unvested restricted shares (in shares)		(337,078)	(295,773)	(280,633)
Less: Unvested contingent restricted shares (in shares)		(547,546)	(515,436)	(465,667)
Weighted average number of shares outstanding used in basic earnings per share (in shares)		172,109,713	164,688,498	155,744,601
Other dilutive securities (shares)		107,364	395,181	551,018
Weighted average number of shares outstanding used in diluted earnings per share (in shares)		172,217,077	165,083,679	156,295,619
Series E Preferred Stock
Basic and Diluted Earnings:
Less: preferred stock dividends		$ 0	$ (13,201)	$ (16,387)
Less: Excess of redemption value over carrying value of preferred shares redeemed	$ (9,856)
Series F Preferred Stock
Basic and Diluted Earnings:
Less: preferred stock dividends		$ (17,940)	$ (17,940)	$ (17,940)