Stockholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended	3 Months Ended
		Apr. 30, 2017	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016	Feb. 28, 2015
Class of Stock [Line Items]
Total allowable shares (in shares)			375,000,000		375,000,000
Net proceeds			$ 49,011	$ 89,135
Total shares issued (in shares)			148,578,933		148,578,933
Stock issuance costs			$ 798	1,380
Common stock dividends			$ 66,781	$ 61,151
Common stock per share (in dollars per share)			$ 0.455	$ 0.435
Subsequent Event
Class of Stock [Line Items]
Common stock, dividends, per share, declared (in dollars per share)		$ 0.455
Series D Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends	[1]		$ 3,598	$ 4,762
Preferred stock per share (in dollars per share)	[1]		$ 0.3128472	$ 0.414063
Series E Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends	[2]		$ 4,097	$ 4,097
Preferred stock per share (in dollars per share)	[2]		$ 0.356250	$ 0.356250
Series F Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends			$ 4,485	$ 0
Preferred stock per share (in dollars per share)			$ 0.32500	$ 0
DRIP
Class of Stock [Line Items]
Total allowable shares (in shares)						16,000,000
Shares of common stock (in shares)			16,320	134,150
Net proceeds			$ 714	$ 5,892
2016 ATM
Class of Stock [Line Items]
Total allowable shares (in shares)			12,000,000
Total shares issued (in shares)			5,310,645
Shares of common stock (in shares)			1,087,355
Average price per share (net) (in dollars per share)			$ 43.92
Net proceeds			$ 47,757
Stock issuance costs	[3]		$ 743
2015 ATM
Class of Stock [Line Items]
Total allowable shares (in shares)			10,000,000
Total shares issued (in shares)			9,852,465
Shares of common stock (in shares)				1,865,260
Average price per share (net) (in dollars per share)				$ 44.00
Net proceeds				$ 82,076
Stock issuance costs	[3]			$ 1,429

[1] The Series D preferred stock was redeemed in February 2017. The dividends paid during the quarter ended March 31, 2017 included accumulated and unpaid dividends through the redemption date.

[2] The Series E preferred stock has no maturity date and will remain outstanding unless redeemed by NNN. The earliest redemption date for the Series E Preferred Stock is May 2018.

[3] Stock issuance costs consist primarily of underwriters' fees and commissions, and legal and accounting fees.