Organization and Summary of Significant Accounting Policies (Computation of Basic and Diluted Earnings per Share) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Basic and Diluted Earnings:
Net earnings attributable to NNN	$ 56,587	$ 65,178
Less: preferred stock dividends	(4,485)	(4,485)
Net earnings attributable to common stockholders	52,102	60,693
Less: Earnings allocated to unvested restricted shares	(151)	(160)
Net earnings used in basic and diluted earnings per share	$ 51,951	$ 60,533
Basic and Diluted Weighted Average Shares Outstanding:
Weighted average number of shares outstanding (in shares)	175,391,723	171,827,815
Less: Unvested restricted shares (in shares)	(288,658)	(311,553)
Less: Unvested contingent restricted shares (in shares)	(513,765)	(477,245)
Weighted average number of shares outstanding used in basic earnings per share (in shares)	174,589,300	171,039,017
Other dilutive securities (in shares)	125,317	192,811
Weighted average number of shares outstanding used in diluted earnings per share (in shares)	174,714,617	171,231,828
Series F Preferred Stock
Basic and Diluted Earnings:
Less: preferred stock dividends	$ (4,485)	$ (4,485)