Organization and Summary of Significant Accounting Policies (Computation of Basic and Diluted Earnings Per Share) (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended								12 Months Ended
	Oct. 31, 2019	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Basic and Diluted Earnings:
Net earnings attributable to NNN		$ 73,786	$ 66,693	$ 78,678	$ 80,023	$ 36,562	$ 82,032	$ 70,573	$ 103,280	$ 299,180	$ 292,447	$ 264,973
Net earnings available to common stockholders										258,183	258,120	217,193
Less: Earnings allocated to unvested restricted shares										(601)	(548)	(531)
Net earnings used in basic and diluted earnings per share										$ 257,582	$ 257,572	$ 216,662
Basic and Diluted Weighted Average Shares Outstanding:
Weighted average number of shares outstanding (in shares)										165,499,707	156,490,901	149,840,116
Less: Unvested restricted shares (in shares)										(295,773)	(280,633)	(285,585)
Less: Unvested contingent restricted shares (in shares)										(515,436)	(465,667)	(443,343)
Weighted average number of shares outstanding used in basic earnings per share (in shares)										164,688,498	155,744,601	149,111,188
Other dilutive securities (shares)										395,181	551,018	321,453
Weighted average number of shares outstanding used in diluted earnings per share (in shares)										165,083,679	156,295,619	149,432,641
Series D Preferred Stock
Basic and Diluted Earnings:
Less: preferred stock dividends										$ 0	$ 0	$ (3,598)
Less: Excess of redemption value over carrying value of preferred shares redeemed										(9,856)	0	(9,855)
Series E Preferred Stock
Basic and Diluted Earnings:
Less: preferred stock dividends										(13,201)	(16,387)	(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)