Organization and Summary of Significant Accounting Policies (Computation of Basic and Diluted Earnings per Share) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Basic and Diluted Earnings:
Net earnings attributable to NNN	$ 46,265	$ 78,678	$ 111,443	$ 158,701
Net earnings attributable to common stockholders	41,780	70,097	102,473	141,537
Less: Earnings allocated to unvested restricted shares	(176)	(134)	(336)	(249)
Net earnings used in basic and diluted earnings per share	$ 41,604	$ 69,963	$ 102,137	$ 141,288
Basic and Diluted Weighted Average Shares Outstanding:
Weighted average number of shares outstanding (in shares)	172,301,757	162,697,005	172,064,786	162,243,958
Less: Unvested restricted stock (in shares)	(342,079)	(265,981)	(326,816)	(249,480)
Less: Unvested contingent restricted shares (in shares)	(570,809)	(537,582)	(524,027)	(492,923)
Weighted average number of shares outstanding used in basic earnings per share (in shares)	171,388,869	161,893,442	171,213,943	161,501,555
Other dilutive securities (in shares)	96,416	458,459	159,873	493,779
Weighted average number of shares outstanding used in diluted earnings per share (in shares)	171,485,285	162,351,901	171,373,816	161,995,334
Series E Preferred Stock
Basic and Diluted Earnings:
Less: preferred stock dividends	$ 0	$ (4,096)	$ 0	$ (8,194)
Series F Preferred Stock
Basic and Diluted Earnings:
Less: preferred stock dividends	$ (4,485)	$ (4,485)	$ (8,970)	$ (8,970)