Notes Payable (Details)		1 Months Ended	3 Months Ended		9 Months Ended
		Mar. 31, 2021 USD ($)	Sep. 30, 2021 USD ($) Instrument	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) Instrument	Sep. 30, 2020 USD ($)	Mar. 31, 2020 USD ($) Instrument	Sep. 30, 2018 USD ($) Instrument	Sep. 30, 2017 USD ($) Instrument	Dec. 31, 2016 USD ($) Instrument	Oct. 31, 2015 USD ($) Instrument	May 31, 2014 USD ($) Instrument
Debt Instrument [Line Items]
Loss deferred in other comprehensive income			$ (1,584,000)		$ (1,584,000)	$ (7,617,000)
Proceeds from notes payable					881,172,000	692,646,000
Payment of debt issuance costs					17,125,000	7,810,000
Make-whole premium					$ 21,328,000	$ 16,679,000
Forward Swap
Debt Instrument [Line Items]
Number of interest rate derivatives terminated | Instrument			2		2		3	2	2	2	4	3
Aggregate notional amount			$ 120,000,000		$ 120,000,000		$ 200,000,000	$ 250,000,000	$ 250,000,000	$ 180,000,000	$ 300,000,000	$ 225,000,000
Loans Payable
Debt Instrument [Line Items]
Debt costs			10,144,000		10,144,000
2051 Notes | Loans Payable
Debt Instrument [Line Items]
Principal amount		$ 450,000,000	$ 450,000,000		$ 450,000,000
Stated interest rate		3.50%	3.50%		3.50%
Aggregate purchase price		$ 441,594,000
Discount	[1]	$ 8,406,000
Effective Rate	[2]	3.602%
2052 Notes | Loans Payable
Debt Instrument [Line Items]
Principal amount	[3]		$ 450,000,000		$ 450,000,000
Stated interest rate	[3]		3.00%		3.00%
Aggregate purchase price	[3]		$ 439,578,000		$ 439,578,000
Discount	[1],[3]		$ 10,422,000		$ 10,422,000
Effective Rate	[2],[3]		3.118%		3.118%
2023 Notes | Loans Payable
Debt Instrument [Line Items]
Stated interest rate		3.30%
Notes payable redeemed		$ 350,000,000
Redemption price, percent of principal amount		100.00%
Make-whole premium		$ (21,328,000)

[1] The note discounts are amortized to interest expense over the respective term of each debt obligation using the effective interest method.

[2] Includes the effects of the discount at issuance.

[3] NNN entered into forward swaps which were hedging the risk of changes in forecasted interest payments on forecasted issuance of long-term debt. Upon the issuance of the 2052 Notes, NNN terminated such derivatives, and the resulting fair value was deferred in accumulated other comprehensive income (loss) and is being amortized over the term of the respective notes using the effective interest method. Additional disclosure is included in Note 6 – Derivatives