Organization and Summary of Significant Accounting Policies (Computation of Basic and Diluted Earnings Per Share) (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended								12 Months Ended
	Feb. 28, 2017	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Basic and Diluted Earnings:
Net earnings attributable to NNN		$ 36,562	$ 82,032	$ 70,573	$ 103,280	$ 72,168	$ 61,120	$ 58,028	$ 73,657	$ 292,447	$ 264,973	$ 239,500
Net earnings available to common stockholders										258,120	217,193	200,877
Less: Earnings attributable to unvested restricted shares										(548)	(531)	(695)
Net earnings used in basic and diluted earnings per share										$ 257,572	$ 216,662	$ 200,182
Basic and Diluted Weighted Average Shares Outstanding:
Weighted average number of shares outstanding (in shares)										156,490,901	149,840,116	145,014,422
Less: Unvested restricted shares (in shares)										(280,633)	(285,585)	(390,522)
Less: Unvested contingent restricted shares (in shares)										(465,667)	(443,343)	(447,676)
Weighted average number of shares outstanding used in basic earnings per share (in shares)										155,744,601	149,111,188	144,176,224
Effects of dilutive securities:
Other (shares)										551,018	321,453	484,409
Weighted average number of shares outstanding used in diluted earnings per share (in shares)										156,295,619	149,432,641	144,660,633
Series D Preferred Stock
Basic and Diluted Earnings:
Less: preferred stock dividends										$ 0	$ (3,598)	$ (19,047)
Less: Excess of redemption value over carrying value of Series D preferred shares redeemed	$ (9,855)									0	(9,855)	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)	$ (17,940)	$ (3,189)