Organization and Summary of Significant Accounting Policies (Computation of Basic and Diluted Earnings Per Share) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Basic and Diluted Earnings:
Net earnings attributable to NNN	$ 72,168	$ 61,120	$ 58,028	$ 73,657	$ 66,092	$ 50,784	$ 51,942	$ 70,683	$ 264,973	$ 239,500	$ 197,836
Net earnings attributable to common stockholders									217,193	200,877	162,402
Less: Earnings attributable to unvested restricted shares									(531)	(695)	(706)
Net earnings used in basic and diluted earnings per share									$ 216,662	$ 200,182	$ 161,696
Basic and Diluted Weighted Average Shares Outstanding:
Weighted average number of shares outstanding (in shares)									149,840,116	145,014,422	134,868,640
Less: Unvested restricted shares (in shares)									(285,585)	(390,522)	(412,505)
Less: Unvested contingent restricted shares (in shares)									(443,343)	(447,676)	(457,461)
Weighted average number of shares outstanding used in basic earnings per share (in shares)									149,111,188	144,176,224	133,998,674
Effects of dilutive securities:
Other (shares)									321,453	484,409	490,742
Weighted average number of shares outstanding used in diluted earnings per share (in shares)									149,432,641	144,660,633	134,489,416
Series D Preferred Stock
Basic and Diluted Earnings:
Less: preferred stock dividends									$ (3,598)	$ (19,047)	$ (19,047)
Less: Excess of redemption value over carrying value of Series D preferred shares redeemed									(9,855)	0	0
Series E Preferred Stock
Basic and Diluted Earnings:
Less: preferred stock dividends									(16,387)	(16,387)	(16,387)
Series F Preferred Stock
Basic and Diluted Earnings:
Less: preferred stock dividends									$ (17,940)	$ (3,189)	$ 0