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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net earnings	$ 79,091	$ 70,583	$ 159,124	$ 173,873
Basic and Diluted Earnings:
Net earnings attributable to NNN	78,678	70,573	158,701	173,854
Net earnings attributable to common stockholders	70,097	61,992	141,537	156,690
Less: Earnings allocated to unvested restricted shares	(134)	(141)	(249)	(273)
Net earnings used in basic and diluted earnings per share	$ 69,963	$ 61,851	$ 141,288	$ 156,417
Basic and Diluted Weighted Average Shares Outstanding:
Weighted average number of shares outstanding (in shares)	162,697,005	154,593,456	162,243,958	154,138,711
Less: Unvested restricted stock (in shares)	(265,981)	(295,444)	(249,480)	(266,690)
Less: Unvested contingent restricted shares (in shares)	(537,582)	(487,320)	(492,923)	(443,656)
Weighted average number of shares outstanding used in basic earnings per share (in shares)	161,893,442	153,810,692	161,501,555	153,428,365
Other dilutive securities (in shares)	458,459	393,246	493,779	411,854
Weighted average number of shares outstanding used in diluted earnings per share (in shares)	162,351,901	154,203,938	161,995,334	153,840,219
Series E Preferred Stock
Basic and Diluted Earnings:
Less: preferred stock dividends	$ (4,096)	$ (4,096)	$ (8,194)	$ (8,194)
Series F Preferred Stock
Basic and Diluted Earnings:
Less: preferred stock dividends	$ (4,485)	$ (4,485)	$ (8,970)	$ (8,970)