Stockholders' Equity (Dividends) (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended	3 Months Ended		9 Months Ended
		Oct. 31, 2021	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Class of Stock [Line Items]
Preferred stock dividends			$ 4,485	$ 4,485	$ 13,455	$ 13,455
Common stock dividends			$ 92,731	$ 89,947	$ 274,550	$ 266,365
Common stock dividends per share (in dollars per share)			$ 0.5300	$ 0.5200	$ 1.5700	$ 1.5500
Common stock dividends declared (in dollars per share)			$ 0.5300	$ 0.5200	$ 1.5700	$ 1.5500
Subsequent event
Class of Stock [Line Items]
Common stock dividends declared (in dollars per share)		$ 0.5300
Series F Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends	[1]		$ 4,485	$ 4,485	$ 13,455	$ 13,455
Preferred stock dividends per depositary share (in dollars per share)	[1]		$ 0.3250	$ 0.3250	$ 0.9750	$ 0.9750
Dividend rate					5.20%

[1] In September 2021, NNN called for the redemption of all outstanding shares of its 5.200% Series F Cumulative Redeemable Preferred Stock (the "Series F Preferred Stock"), including all accrued and unpaid dividends through, but not including, the redemption date, on October 16, 2021