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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Basic and Diluted Earnings:
Net earnings attributable to NNN	$ 66,693	$ 82,032	$ 225,394	$ 255,886
Net earnings attributable to common stockholders	58,111	73,450	199,648	230,140
Less: Earnings allocated to unvested restricted shares	(163)	(147)	(412)	(412)
Net earnings used in basic and diluted earnings per share	$ 57,948	$ 73,303	$ 199,236	$ 229,728
Basic and Diluted Weighted Average Shares Outstanding:
Weighted average number of shares outstanding (in shares)	165,737,947	157,634,757	163,421,419	155,316,866
Less: Unvested restricted stock (in shares)	(316,856)	(294,453)	(272,185)	(276,046)
Less: Unvested contingent restricted shares (in shares)	(537,582)	(487,320)	(507,973)	(458,371)
Weighted average number of shares outstanding used in basic earnings per share (in shares)	164,883,509	156,852,984	162,641,261	154,582,449
Other dilutive securities (in shares)	478,222	433,181	484,802	425,408
Weighted average number of shares outstanding used in diluted earnings per share (in shares)	165,361,731	157,286,165	163,126,063	155,007,857
Series E Preferred Stock
Basic and Diluted Earnings:
Less: preferred stock dividends	$ (4,097)	$ (4,097)	$ (12,291)	$ (12,291)
Series F Preferred Stock
Basic and Diluted Earnings:
Less: preferred stock dividends	$ (4,485)	$ (4,485)	$ (13,455)	$ (13,455)

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