Organization and Summary of Significant Accounting Policies (Policies)	9 Months Ended
Sep. 30, 2020
Accounting Policies [Abstract]
Principles of Consolidation	Principles of Consolidation – NNN’s condensed consolidated financial statements include the accounts of each of the respective majority owned and controlled affiliates, including transactions whereby NNN has been determined to be the primary beneficiary in accordance with the Financial Accounting Standards Board (“FASB”) Accounting Standards Codifications ("ASC") guidance included in Consolidation. All significant intercompany account balances and transactions have been eliminated.
Real Estate Portfolio and Impairment	Real Estate Portfolio – NNN records the acquisition of real estate at cost, including acquisition and closing costs. The cost of Properties developed or funded by NNN includes direct and indirect costs of construction, property taxes, interest and other miscellaneous costs incurred during the development period until the project is substantially complete and available for occupancy. NNN recorded $1,218,000 and $797,000 in capitalized interest during the development period for the nine months ended September 30, 2020 and 2019, respectively, of which $332,000 and $327,000 was recorded during the quarters ended September 30, 2020 and 2019, respectively. Purchase Accounting for Acquisition of Real Estate Subject to a Lease – In accordance with the FASB guidance on business combinations, consideration for the real estate acquired is allocated to the acquired tangible assets, consisting of land, building and tenant improvements, and, if applicable, to identified intangible assets and liabilities, consisting of the value of above-market and below-market leases and the value of in-place leases, as applicable, based on their respective fair values. The fair value estimate is sensitive to significant assumptions, such as establishing a range of relevant market assumptions for land, building and rent and where the acquired property falls within that range. These market assumptions for land, building and rent use the most relevant comparable properties for an acquisition. The final range relies upon ranking comparable properties' attributes from most similar to least similar. The fair value of the tangible assets of an acquired property is determined by valuing the property as if it were vacant, and the "as-if-vacant" value is then allocated to land, building and tenant improvements based on the determination of their fair values. In allocating the fair value of the identified intangible assets and liabilities of an acquired property, above-market and below-market in-place lease values are recorded as other assets or liabilities based on the present value (using an interest rate which reflects the risks associated with the leases acquired) of the difference between (i) the contractual amounts to be paid pursuant to the in-place leases, and (ii) management’s estimate of fair market lease rates for the corresponding in-place leases, measured over a period equal to the remaining term of the lease and the applicable option terms if it is probable that the tenant will exercise options. The capitalized above-market lease values are amortized as a reduction of rental income over the remaining terms of the respective leases. The capitalized below-market lease values are amortized as an increase to rental income over the initial term unless the Company believes that it is likely that the tenant will renew the lease for an option term whereby the Company amortizes the value attributable to the renewal over the renewal period. The aggregate value of other acquired intangible assets, consisting of in-place leases, is measured by the excess of (i) the purchase price paid for a property after adjusting existing in-place leases to market rental rates over (ii) the estimated fair value of the property as-if-vacant, determined as set forth above. The value of in-place leases exclusive of the value of above-market and below-market in-place leases is amortized to expense over the remaining non-cancelable periods of the respective leases. If a lease were to be terminated prior to its stated expiration, all unamortized amounts relating to that lease would be written off in that period. The value of tenant relationships is reviewed on individual transactions to determine if future value was derived from the acquisition. Impairment – Real Estate – Based upon certain events or changes in circumstances, management periodically assesses its Properties for possible impairment whenever the carrying value of the asset, including accrued rental income, may not be recoverable through operations. Events or circumstances that may occur include significant changes in real estate market conditions and the ability of NNN to re-lease or sell properties that are currently vacant or become vacant in a reasonable period of time. Management evaluates whether an impairment in carrying value has occurred by comparing the estimated future cash flows (undiscounted and without interest charges), and the residual value of the real estate, with the carrying value of the individual asset. The future undiscounted cash flows are primarily driven by estimated future market rents. If an impairment is indicated, a loss will be recorded for the amount by which the carrying value of the asset exceeds its estimated fair value. NNN's Properties are leased primarily to retail tenants under long-term net leases and primarily held for investment. Generally, NNN’s Property leases provide for initial terms of 10 to 20 years, which provide for cash flows over this term. NNN intends to hold these assets for the long-term, therefore, a temporary change in cash flows due to COVID-19 alone would not be an indicator of impairment.
Lease Accounting, Lessor	Lease Accounting – In accordance with FASB Accounting Standards Update ("ASU") 2016-02, "Leases (Topic 842)," ("ASC 842"), NNN reviews the collectability of its accounts receivable, including accrued rental income, related to rents, expense reimbursements and other revenues. NNN analyzes accounts receivable and historical bad debt levels, tenant credit-worthiness and current economic trends when evaluating the probability of collection. In addition, tenants in bankruptcy are analyzed and considerations are made in connection with the expected recovery of pre-petition and post-petition bankruptcy claims. NNN includes an allowance for doubtful accounts in rental income on the Condensed Consolidated Statements of Income and Comprehensive Income. At the point NNN deems the collection of lease payments not probable, a bad debt is recognized for any outstanding receivable and any related accrued rent and, subsequently, any lease revenue is only recognized when cash receipts are received. As a result of the review of tenant receivables’ collectability, NNN recorded a write-off of $14,758,000 of outstanding receivables and related accrued rent during the quarter and nine months ended September 30, 2020, and subsequently reclassified certain tenants as cash basis for accounting purposes. During the quarter and nine months ended September 30, 2020, NNN recognized revenue on a cash basis of $2,203,000 and $2,406,000, respectively. NNN did not recognize revenue on a cash basis during the quarter and nine months ended September 30, 2019. As of September 30, 2020, approximately four percent of total Properties, and approximately six percent of aggregate gross leasable area held in the Property Portfolio, was leased to six tenants that NNN has determined to recognize revenue from on a cash basis. In accordance with ASC 842, NNN recorded Right-Of-Use ("ROU") assets and operating lease liabilities of approximately $7,735,000 and $10,155,000 respectively, as of January 1, 2019. In April 2020, the FASB issued interpretive guidance relating to the accounting for lease concessions provided as a result of COVID-19. In this guidance, entities can elect not to apply lease modification accounting with respect to such lease concessions and instead, treat the concession as if it was a part of the existing contract. This guidance is only applicable to COVID-19 related lease concessions that do not result in a substantial increase in the rights of the lessor or the obligations of the lessee. NNN has elected to make this policy election for COVID-19 lease concessions, including the rent deferral lease amendments effective during the nine months ended September 30, 2020.
Lease Accounting, Lessee	Lease Accounting – In accordance with FASB Accounting Standards Update ("ASU") 2016-02, "Leases (Topic 842)," ("ASC 842"), NNN reviews the collectability of its accounts receivable, including accrued rental income, related to rents, expense reimbursements and other revenues. NNN analyzes accounts receivable and historical bad debt levels, tenant credit-worthiness and current economic trends when evaluating the probability of collection. In addition, tenants in bankruptcy are analyzed and considerations are made in connection with the expected recovery of pre-petition and post-petition bankruptcy claims. NNN includes an allowance for doubtful accounts in rental income on the Condensed Consolidated Statements of Income and Comprehensive Income. At the point NNN deems the collection of lease payments not probable, a bad debt is recognized for any outstanding receivable and any related accrued rent and, subsequently, any lease revenue is only recognized when cash receipts are received. As a result of the review of tenant receivables’ collectability, NNN recorded a write-off of $14,758,000 of outstanding receivables and related accrued rent during the quarter and nine months ended September 30, 2020, and subsequently reclassified certain tenants as cash basis for accounting purposes. During the quarter and nine months ended September 30, 2020, NNN recognized revenue on a cash basis of $2,203,000 and $2,406,000, respectively. NNN did not recognize revenue on a cash basis during the quarter and nine months ended September 30, 2019. As of September 30, 2020, approximately four percent of total Properties, and approximately six percent of aggregate gross leasable area held in the Property Portfolio, was leased to six tenants that NNN has determined to recognize revenue from on a cash basis. In accordance with ASC 842, NNN recorded Right-Of-Use ("ROU") assets and operating lease liabilities of approximately $7,735,000 and $10,155,000 respectively, as of January 1, 2019. In April 2020, the FASB issued interpretive guidance relating to the accounting for lease concessions provided as a result of COVID-19. In this guidance, entities can elect not to apply lease modification accounting with respect to such lease concessions and instead, treat the concession as if it was a part of the existing contract. This guidance is only applicable to COVID-19 related lease concessions that do not result in a substantial increase in the rights of the lessor or the obligations of the lessee. NNN has elected to make this policy election for COVID-19 lease concessions, including the rent deferral lease amendments effective during the nine months ended September 30, 2020.
Debt Costs	Debt Costs – Notes Payable – Debt costs incurred in connection with the issuance of NNN’s notes payable have been deferred and are being amortized to interest expense over the term of the respective debt obligation using the effective interest method. These costs of $31,140,000 and $26,932,000, as of September 30, 2020 and December 31, 2019, respectively, are included in notes payable on the Condensed Consolidated Balance Sheets net of accumulated amortization of $8,705,000 and $8,962,000, respectively.
Credit Losses on Financial Instruments	Credit Losses on Financial Instruments – Effective January 1, 2020, NNN adopted FASB ASU 2016-13, “Financial Instruments - Credit Losses (Topic 326),” (“ASC 326”). The amendments in this update replace the incurred loss impairment methodology in current GAAP with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to inform credit loss estimates. ASU 326 requires entities to estimate an expected lifetime credit loss on financial assets ranging from short-term trade accounts receivable to long-term financings. The new guidance requires a lifetime credit loss expected at inception and requires pooling of assets, which share similar risk characteristics. NNN is required to evaluate current economic conditions, as well as, make future expectations of economic conditions. In addition, the measurement of the expected credit loss is over the asset’s contractual term. As of September 30, 2020, NNN had a mortgage receivable of $2,569,000 included in other assets on the Condensed Consolidated Balance Sheets, net of $164,000 allowance for credit loss. NNN measures the allowance for credit loss based on the fair value of the collateral and the historical collectability trend analysis over 15 years. Adoption of ASC 326 did not materially impact NNN’s financial position or results of operations and had no impact on cash flows.
Earnings Per Share	Earnings Per Share – Earnings per share have been computed pursuant to the FASB guidance included in Earnings Per Share. The guidance requires classification of the Company’s unvested restricted share units, which carry rights to receive nonforfeitable dividends, as participating securities requiring the two-class method of computing earnings per share. Under the two-class method, earnings per common share are computed by dividing the sum of distributed earnings to common stockholders and undistributed earnings allocated to common stockholders by the weighted average number of common shares outstanding for the period. In applying the two-class method, undistributed earnings are allocated to both common shares and participating securities based on the weighted average shares outstanding during the period.
Fair Value Measurement	Fair Value Measurement – NNN’s estimates of fair value of financial and non-financial assets and liabilities are based on the framework established in the fair value accounting guidance. The framework specifies a hierarchy of valuation inputs which was established to increase consistency, clarity and comparability in fair value measurements and related disclosures. The guidance describes a fair value hierarchy based upon three levels of inputs that may be used to measure fair value, two of which are considered observable and one that is considered unobservable. The following describes the three levels: •Level 1 – Valuation is based upon quoted prices in active markets for identical assets or liabilities. •Level 2 – Valuation is based upon inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities, quoted prices in markets that are not active or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. •Level 3 – Valuation is generated from model-based techniques that use at least one significant assumption not observable in the market. These unobservable assumptions reflect estimates of assumptions that market participants would use in pricing the asset or liability. Valuation techniques include option pricing models, discounted cash flow models and similar techniques.
New Accounting Pronouncements	New Accounting Pronouncements – In December 2019, the FASB issued ASU 2019-12, “Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes,” ("ASU 2019-12"), effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2020. The amendments simplify the accounting for income taxes by removing certain exceptions to the general principles in Topic 740. The amendments also improve consistent application of and simplify GAAP for other areas of Topic 740 by clarifying and amending existing guidance. The adoption of ASU 2019-12 will not have a significant impact on NNN's financial position or results of operations.
Use of Estimates	Use of Estimates – Management has made a number of estimates and assumptions relating to the reporting of assets and liabilities, revenues and expenses and the disclosure of contingent assets and liabilities to prepare these condensed consolidated financial statements in conformity with GAAP. Significant estimates include provisions for impairment and allowances for certain assets, accruals, useful lives of assets and purchase price allocation. Actual results could differ from those estimates.
Reclassification	Reclassification – Certain items in the prior year’s condensed consolidated financial statements and notes to condensed consolidated financial statements have been reclassified to conform to the 2020 presentation.

Organization and Summary of Significant Accounting Policies (Policies)

9 Months Ended

Sep. 30, 2020

Principles of Consolidation – NNN’s condensed consolidated financial statements include the accounts of each of the respective majority owned and controlled affiliates, including transactions whereby NNN has been determined to be the primary beneficiary in accordance with the Financial Accounting Standards Board (“FASB”) Accounting Standards Codifications ("ASC") guidance included in Consolidation. All significant intercompany account balances and transactions have been eliminated.

Real Estate Portfolio and Impairment

Real Estate Portfolio – NNN records the acquisition of real estate at cost, including acquisition and closing costs. The cost of Properties developed or funded by NNN includes direct and indirect costs of construction, property taxes, interest and other miscellaneous costs incurred during the development period until the project is substantially complete and available for occupancy. NNN recorded $1,218,000 and $797,000 in capitalized interest during the development period for the nine months ended September 30, 2020 and 2019, respectively, of which $332,000 and $327,000 was recorded during the quarters ended September 30, 2020 and 2019, respectively.

Purchase Accounting for Acquisition of Real Estate Subject to a Lease – In accordance with the FASB guidance on business combinations, consideration for the real estate acquired is allocated to the acquired tangible assets, consisting of land, building and tenant improvements, and, if applicable, to identified intangible assets and liabilities, consisting of the value of above-market and below-market leases and the value of in-place leases, as applicable, based on their respective fair values.

The fair value estimate is sensitive to significant assumptions, such as establishing a range of relevant market assumptions for land, building and rent and where the acquired property falls within that range. These market assumptions for land, building and rent use the most relevant comparable properties for an acquisition. The final range relies upon ranking comparable properties' attributes from most similar to least similar.

The fair value of the tangible assets of an acquired property is determined by valuing the property as if it were vacant, and the "as-if-vacant" value is then allocated to land, building and tenant improvements based on the determination of their fair values.

In allocating the fair value of the identified intangible assets and liabilities of an acquired property, above-market and below-market in-place lease values are recorded as other assets or liabilities based on the present value (using an interest rate which reflects the risks associated with the leases acquired) of the difference between (i) the contractual amounts to be paid pursuant to the in-place leases, and (ii) management’s estimate of fair market lease rates for the corresponding in-place leases, measured over a period equal to the remaining term of the lease and the applicable option terms if it is probable that the tenant will exercise options. The capitalized above-market lease values are amortized as a reduction of rental income over the remaining terms of the respective leases. The capitalized below-market lease values are amortized as an increase to rental income over the initial term unless the Company believes that it is likely that the tenant will renew the lease for an option term whereby the Company amortizes the value attributable to the renewal over the renewal period.

The aggregate value of other acquired intangible assets, consisting of in-place leases, is measured by the excess of (i) the purchase price paid for a property after adjusting existing in-place leases to market rental rates over (ii) the estimated fair value of the property as-if-vacant, determined as set forth above. The value of in-place leases exclusive of the value of above-market and below-market in-place leases is amortized to expense over the remaining non-cancelable periods of the respective leases. If a lease were to be terminated prior to its stated expiration, all unamortized amounts relating to that lease would be written off in

that period. The value of tenant relationships is reviewed on individual transactions to determine if future value was derived from the acquisition.

Impairment – Real Estate – Based upon certain events or changes in circumstances, management periodically assesses its Properties for possible impairment whenever the carrying value of the asset, including accrued rental income, may not be recoverable through operations. Events or circumstances that may occur include significant changes in real estate market conditions and the ability of NNN to re-lease or sell properties that are currently vacant or become vacant in a reasonable period of time. Management evaluates whether an impairment in carrying value has occurred by comparing the estimated future cash flows (undiscounted and without interest charges), and the residual value of the real estate, with the carrying value of the individual asset. The future undiscounted cash flows are primarily driven by estimated future market rents. If an impairment is indicated, a loss will be recorded for the amount by which the carrying value of the asset exceeds its estimated fair value. NNN's Properties are leased primarily to retail tenants under long-term net leases and primarily held for investment. Generally, NNN’s Property leases provide for initial terms of 10 to 20 years, which provide for cash flows over this term. NNN intends to hold these assets for the long-term, therefore, a temporary change in cash flows due to COVID-19 alone would not be an indicator of impairment.

Lease Accounting, Lessor

Lease Accounting – In accordance with FASB Accounting Standards Update ("ASU") 2016-02, "Leases (Topic 842)," ("ASC 842"), NNN reviews the collectability of its accounts receivable, including accrued rental income, related to rents, expense reimbursements and other revenues. NNN analyzes accounts receivable and historical bad debt levels, tenant credit-worthiness and current economic trends when evaluating the probability of collection. In addition, tenants in bankruptcy are analyzed and considerations are made in connection with the expected recovery of pre-petition and post-petition bankruptcy claims. NNN includes an allowance for doubtful accounts in rental income on the Condensed Consolidated Statements of Income and Comprehensive Income. At the point NNN deems the collection of lease payments not probable, a bad debt is recognized for any outstanding receivable and any related accrued rent and, subsequently, any lease revenue is only recognized when cash receipts are received. As a result of the review of tenant receivables’ collectability, NNN recorded a write-off of $14,758,000 of outstanding receivables and related accrued rent during the quarter and nine months ended September 30, 2020, and subsequently reclassified certain tenants as cash basis for accounting purposes.

During the quarter and nine months ended September 30, 2020, NNN recognized revenue on a cash basis of $2,203,000 and $2,406,000, respectively. NNN did not recognize revenue on a cash basis during the quarter and nine months ended September 30, 2019. As of September 30, 2020, approximately four percent of total Properties, and approximately six percent of aggregate gross leasable area held in the Property Portfolio, was leased to six tenants that NNN has determined to recognize revenue from on a cash basis.

In accordance with ASC 842, NNN recorded Right-Of-Use ("ROU") assets and operating lease liabilities of approximately $7,735,000 and $10,155,000 respectively, as of January 1, 2019.

In April 2020, the FASB issued interpretive guidance relating to the accounting for lease concessions provided as a result of COVID-19. In this guidance, entities can elect not to apply lease modification accounting with respect to such lease concessions and instead, treat the concession as if it was a part of the existing contract. This guidance is only applicable to COVID-19 related lease concessions that do not result in a substantial increase in the rights of the lessor or the obligations of the lessee. NNN has elected to make this policy election for COVID-19 lease concessions, including the rent deferral lease amendments effective during the nine months ended September 30, 2020.

Lease Accounting, Lessee

In accordance with ASC 842, NNN recorded Right-Of-Use ("ROU") assets and operating lease liabilities of approximately $7,735,000 and $10,155,000 respectively, as of January 1, 2019.

Debt Costs

Debt Costs – Notes Payable – Debt costs incurred in connection with the issuance of NNN’s notes payable have been deferred and are being amortized to interest expense over the term of the respective debt obligation using the effective interest method. These costs of $31,140,000 and $26,932,000, as of September 30, 2020 and December 31, 2019, respectively, are included in notes payable on the Condensed Consolidated Balance Sheets net of accumulated amortization of $8,705,000 and $8,962,000, respectively.

Credit Losses on Financial Instruments

Credit Losses on Financial Instruments – Effective January 1, 2020, NNN adopted FASB ASU 2016-13, “Financial Instruments - Credit Losses (Topic 326),” (“ASC 326”). The amendments in this update replace the incurred loss impairment methodology in current GAAP with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to inform credit loss estimates.

ASU 326 requires entities to estimate an expected lifetime credit loss on financial assets ranging from short-term trade accounts receivable to long-term financings. The new guidance requires a lifetime credit loss expected at inception and requires pooling of assets, which share similar risk characteristics. NNN is required to evaluate current economic conditions, as well as, make future expectations of economic conditions. In addition, the measurement of the expected credit loss is over the asset’s contractual term.

As of September 30, 2020, NNN had a mortgage receivable of $2,569,000 included in other assets on the Condensed Consolidated Balance Sheets, net of $164,000 allowance for credit loss. NNN measures the allowance for credit loss based on the fair value of the collateral and the historical collectability trend analysis over 15 years.

Adoption of ASC 326 did not materially impact NNN’s financial position or results of operations and had no impact on cash flows.

Earnings Per Share

Earnings Per Share – Earnings per share have been computed pursuant to the FASB guidance included in Earnings Per Share. The guidance requires classification of the Company’s unvested restricted share units, which carry rights to receive nonforfeitable dividends, as participating securities requiring the two-class method of computing earnings per share. Under the two-class method, earnings per common share are computed by dividing the sum of distributed earnings to common stockholders and undistributed earnings allocated to common stockholders by the weighted average number of common shares outstanding for the period. In applying the two-class method, undistributed earnings are allocated to both common shares and participating securities based on the weighted average shares outstanding during the period.

Fair Value Measurement

Fair Value Measurement – NNN’s estimates of fair value of financial and non-financial assets and liabilities are based on the framework established in the fair value accounting guidance. The framework specifies a hierarchy of valuation inputs which was established to increase consistency, clarity and comparability in fair value measurements and related disclosures. The guidance describes a fair value hierarchy based upon three levels of inputs that may be used to measure fair value, two of which are considered observable and one that is considered unobservable. The following describes the three levels:

•Level 1 – Valuation is based upon quoted prices in active markets for identical assets or liabilities.

•Level 2 – Valuation is based upon inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities, quoted prices in markets that are not active or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities.

•Level 3 – Valuation is generated from model-based techniques that use at least one significant assumption not observable in the market. These unobservable assumptions reflect estimates of assumptions that market participants would use in pricing the asset or liability. Valuation techniques include option pricing models, discounted cash flow models and similar techniques.

New Accounting Pronouncements

New Accounting Pronouncements – In December 2019, the FASB issued ASU 2019-12, “Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes,” ("ASU 2019-12"), effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2020. The amendments simplify the accounting for income taxes by removing certain exceptions to the general principles in Topic 740. The amendments also improve consistent application of and simplify GAAP for other areas of Topic 740 by clarifying and amending existing guidance. The adoption of ASU 2019-12 will not have a significant impact on NNN's financial position or results of operations.

Use of Estimates

Use of Estimates – Management has made a number of estimates and assumptions relating to the reporting of assets and liabilities, revenues and expenses and the disclosure of contingent assets and liabilities to prepare these condensed consolidated financial statements in conformity with GAAP. Significant estimates include provisions for impairment and allowances for certain assets, accruals, useful lives of assets and purchase price allocation. Actual results could differ from those estimates.

Reclassification

Reclassification – Certain items in the prior year’s condensed consolidated financial statements and notes to condensed consolidated financial statements have been reclassified to conform to the 2020 presentation.