Organization and Summary of Significant Accounting Policies (Computation of Basic and Diluted Earnings per Share) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Basic and Diluted Earnings:
Net earnings attributable to NNN	$ 56,069	$ 66,693	$ 167,512	$ 225,394
Net earnings attributable to common stockholders	51,584	58,111	154,057	199,648
Less: Earnings allocated to unvested restricted shares	(179)	(163)	(516)	(412)
Net earnings used in basic and diluted earnings per share	$ 51,405	$ 57,948	$ 153,541	$ 199,236
Basic and Diluted Weighted Average Shares Outstanding:
Weighted average number of shares outstanding (in shares)	173,596,374	165,737,947	172,579,042	163,421,419
Less: Unvested restricted stock (in shares)	(344,429)	(316,856)	(332,730)	(272,185)
Less: Unvested contingent restricted shares (in shares)	(570,809)	(537,582)	(539,735)	(507,973)
Weighted average number of shares outstanding used in basic earnings per share (in shares)	172,681,136	164,883,509	171,706,577	162,641,261
Other dilutive securities (in shares)	101,130	478,222	108,800	484,802
Weighted average number of shares outstanding used in diluted earnings per share (in shares)	172,782,266	165,361,731	171,815,377	163,126,063
Series E Preferred Stock
Basic and Diluted Earnings:
Less: preferred stock dividends	$ 0	$ (4,097)	$ 0	$ (12,291)
Series F Preferred Stock
Basic and Diluted Earnings:
Less: preferred stock dividends	$ (4,485)	$ (4,485)	$ (13,455)	$ (13,455)