Summary of Significant Accounting Policies (Policies)	9 Months Ended
Sep. 30, 2020
Accounting Policies [Abstract]
Basis of Presentation	The consolidated financial statements of Piedmont have been prepared in accordance with the rules and regulations of the Securities and Exchange Commission (the “SEC”), including the instructions to Form 10-Q and Article 10 of Regulation S-X, and do not include all of the information and footnotes required by GAAP for complete financial statements. In the opinion of management, the statements for the unaudited interim periods presented include all adjustments, which are of a normal and recurring nature, necessary for a fair presentation of the results for such periods. Results for these interim periods are not necessarily indicative of a full year’s results.
Principles of Consolidation	Piedmont’s consolidated financial statements include the accounts of Piedmont, Piedmont’s wholly-owned subsidiaries, any variable interest entity ("VIE") for which Piedmont or any of its wholly-owned subsidiaries is considered to have the power to direct the activities of the entity and the obligation to absorb losses/right to receive benefits, or any entity in which Piedmont or any of its wholly-owned subsidiaries owns a controlling interest. In determining whether Piedmont or Piedmont OP has a controlling interest, the following factors, among others, are considered: equity ownership, voting rights, protective rights of investors, and participatory rights of investors. For further information, refer to the financial statements and footnotes included in Piedmont’s Annual Report on Form 10-K for the year ended December 31, 2019. All intercompany balances and transactions have been eliminated upon consolidation. Further, Piedmont has formed special purpose entities to acquire and hold real estate. Each special purpose entity is a separate legal entity. Consequently, the assets of these special purpose entities are not available to all creditors of Piedmont. The assets owned by these special purpose entities are being reported on a consolidated basis with Piedmont’s assets for financial reporting purposes only.
Use of Estimates	Use of Estimates The preparation of the accompanying consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the accompanying consolidated financial statements and notes. The most significant of these estimates include the underlying cash flows and holding periods used in assessing impairment, judgements regarding the recoverability of goodwill, and the assessment of the collectibility of receivables. Future impacts of the COVID-19 pandemic on Piedmont and its tenants may affect these and other estimates used in the preparation of these financial statements. While Piedmont has made, what it believes to be, appropriate accounting estimates based on the facts and circumstances available as of the reporting date, actual results could materially differ from those estimates.
Income Taxes	Income Taxes Piedmont has elected to be taxed as a REIT under the Internal Revenue Code of 1986, as amended, and has operated as such, beginning with its taxable year ended December 31, 1998. To qualify as a REIT, Piedmont must meet certain organizational and operational requirements, including a requirement to distribute at least 90% of its annual REIT taxable income. As a REIT, Piedmont is generally not subject to federal income taxes, subject to fulfilling, among other things, its taxable income distribution requirement. Piedmont is subject to certain taxes related to the operations of properties in certain locations, as well as operations conducted by its taxable REIT subsidiary, POH, which have been provided for in the financial statements.
Intangible Assets And Liabilities Resulting From Purchasing Real Estate Assets	Intangible Assets and Liabilities Resulting from Purchasing Real Estate Assets Upon the acquisition of real properties, Piedmont allocates the purchase price of the properties to tangible assets, consisting of land, building, site improvements, and identified intangible assets and liabilities, including the value of in-place leases, based in each case on Piedmont's estimate of their fair values in accordance with Accounting Standards Codification ("ASC") 820 Fair Value Measurements.
Recent Accounting Pronouncements	Accounting Pronouncements and Amendments Adopted during the Nine Months Ended September 30, 2020 Reference Rate Reform Relief Accounting Standards Update No. 2020-04, Reference Rate Reform (Topic 848) ("ASU 2020-04"), was issued in March 2020. ASU 2020-04 contains practical expedients for reference rate reform related activities that impact debt, leases, derivatives and other contracts. The guidance in ASU 2020-04 is optional and may be elected over time as reference rate reform activities occur. During the nine months ended September 30, 2020, Piedmont elected to apply the hedge accounting expedients related to probability and the assessments of effectiveness for future LIBOR-indexed cash flows to assume that the index upon which future hedged transactions will be based matches the index on the corresponding derivatives. Application of these expedients preserves the presentation of derivatives consistent with past presentation. Piedmont continues to evaluate the impact of the guidance and may apply other elections as applicable as additional changes in the market occur. Financial Instruments- Credit Loss Amendments On January 1, 2020, Piedmont adopted ASU No. 2016-13, Financial Instruments—Credit Losses (Topic 326), Measurement of Credit Losses on Financial Instruments, as well as ASU No. 2019-04, Codification Improvements to Topic 326, Financial Instruments - Credit Losses, Topic 815, Derivatives and Hedging, and Topic 825, Financial Instruments, and ASU No. 2019-05, Financial Instruments- Credit Losses: Targeted Transition Relief (collectively the "Credit Loss Amendments"). The provisions of the Credit Loss Amendments replace the "incurred loss" approach with an "expected loss" model for impairing trade and other receivables, held-to-maturity debt securities, net investment in leases, and off-balance-sheet credit exposures, which will generally result in earlier recognition of allowances for credit losses. However, the Financial Accounting Standards Board (the "FASB") also issued ASU No. 2018-19 Codification Improvements to Topic 326, Financial Instruments - Credit Losses, which is effective concurrent with the Credit Loss Amendments, and excludes receivables arising from operating leases from the scope of the Credit Loss Amendments and affirms that such receivables should be evaluated for collectibility as prescribed by ASC 842 Leases. As substantially all of Piedmont's receivables are operating lease receivables there was no material impact to Piedmont's accompanying consolidated financial statements or disclosures as a result of adoption of the Credit Loss Amendments. During the nine months ended September 30, 2020, the FASB issued a Staff Q&A on Topic 842 and Topic 840 (lease accounting guidance): Accounting for lease concessions related to the effects of the COVID-19 pandemic. Generally, changes to payment terms not contemplated by the lease contract should be accounted for under Topic 842 as a lease modification. The FASB staff has provided relief from this modification guidance through an accounting policy election, provided that changes to the payment terms do not result in a substantial increase in the rights of either the lessee or the lessor under the lease. Piedmont has elected not to apply the relief provided by the FASB Staff, and has instead accounted for all rent relief agreements as result of COVID-19 as lease modifications. See further details concerning rent relief agreements with Piedmont's tenants in Note 7 below. Reclassifications Certain prior period amounts presented in the accompanying consolidated balance sheets have been reclassified as of December 31, 2019 to conform to the current period financial statement presentation related to the 1901 Market Street building, which was classified as held for sale as of March 31, 2020, and sold on June 25, 2020. (see Note 8).
Risk Management Objective of Using Derivatives	Risk Management Objective of Using Derivatives In addition to operational risks which arise in the normal course of business, Piedmont is exposed to economic risks such as interest rate, liquidity, and credit risk. In certain situations, Piedmont has entered into derivative financial instruments such as interest rate swap agreements and other similar agreements to manage interest rate risk exposure arising from current or future variable rate debt transactions. Interest rate swap agreements involve the receipt or payment of future known and uncertain cash amounts, the value of which are determined by interest rates. Piedmont’s objective in using interest rate derivatives is to add stability to interest expense and to manage its exposure to interest rate movements.

Summary of Significant Accounting Policies (Policies)

9 Months Ended

Sep. 30, 2020

The consolidated financial statements of Piedmont have been prepared in accordance with the rules and regulations of the Securities and Exchange Commission (the “SEC”), including the instructions to Form 10-Q and Article 10 of Regulation S-X, and do not include all of the information and footnotes required by GAAP for complete financial statements. In the opinion of management, the statements for the unaudited interim periods presented include all adjustments, which are of a normal and recurring nature, necessary for a fair presentation of the results for such periods. Results for these interim periods are not necessarily indicative of a full year’s results.

Principles of Consolidation

Piedmont’s consolidated financial statements include the accounts of Piedmont, Piedmont’s wholly-owned subsidiaries, any variable interest entity ("VIE") for which Piedmont or any of its wholly-owned subsidiaries is considered to have the power to direct the activities of the entity and the obligation to absorb losses/right to receive benefits, or any entity in which Piedmont or any of its wholly-owned subsidiaries owns a controlling interest. In determining whether Piedmont or Piedmont OP has a controlling interest, the following factors, among others, are considered: equity ownership, voting rights, protective rights of investors, and participatory rights of investors. For further information, refer to the financial statements and footnotes included in Piedmont’s Annual Report on Form 10-K for the year ended December 31, 2019.

All intercompany balances and transactions have been eliminated upon consolidation.

Further, Piedmont has formed special purpose entities to acquire and hold real estate. Each special purpose entity is a separate legal entity. Consequently, the assets of these special purpose entities are not available to all creditors of Piedmont. The assets owned by these special purpose entities are being reported on a consolidated basis with Piedmont’s assets for financial reporting purposes only.

Use of Estimates

The preparation of the accompanying consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the accompanying consolidated financial statements and notes. The most significant of these estimates include the underlying cash flows and holding periods used in assessing impairment, judgements regarding the recoverability of goodwill, and the assessment of the collectibility of receivables. Future impacts of the COVID-19 pandemic on Piedmont and its tenants may affect these and other estimates used in the preparation of these financial statements. While Piedmont has made, what it believes to be, appropriate accounting estimates based on the facts and circumstances available as of the reporting date, actual results could materially differ from those estimates.

Income Taxes

Piedmont has elected to be taxed as a REIT under the Internal Revenue Code of 1986, as amended, and has operated as such, beginning with its taxable year ended December 31, 1998. To qualify as a REIT, Piedmont must meet certain organizational and operational requirements, including a requirement to distribute at least 90% of its annual REIT taxable income. As a REIT, Piedmont is generally not subject to federal income taxes, subject to fulfilling, among other things, its taxable income distribution requirement. Piedmont is subject to certain taxes related to the operations of properties in certain locations, as well as operations conducted by its taxable REIT subsidiary, POH, which have been provided for in the financial statements.

Intangible Assets And Liabilities Resulting From Purchasing Real Estate Assets

Intangible Assets and Liabilities Resulting from Purchasing Real Estate Assets

Upon the acquisition of real properties, Piedmont allocates the purchase price of the properties to tangible assets, consisting of land, building, site improvements, and identified intangible assets and liabilities, including the value of in-place leases, based in each case on Piedmont's estimate of their fair values in accordance with Accounting Standards Codification ("ASC") 820 Fair Value Measurements.

Recent Accounting Pronouncements

Accounting Pronouncements and Amendments Adopted during the Nine Months Ended September 30, 2020

Reference Rate Reform Relief

Accounting Standards Update No. 2020-04, Reference Rate Reform (Topic 848) ("ASU 2020-04"), was issued in March 2020. ASU 2020-04 contains practical expedients for reference rate reform related activities that impact debt, leases, derivatives and other contracts. The guidance in ASU 2020-04 is optional and may be elected over time as reference rate reform activities occur. During the nine months ended September 30, 2020, Piedmont elected to apply the hedge accounting expedients related to probability and the assessments of effectiveness for future LIBOR-indexed cash flows to assume that the index upon which future hedged transactions will be based matches the index on the corresponding derivatives. Application of these expedients preserves the presentation of derivatives consistent with past presentation. Piedmont continues to evaluate the impact of the guidance and may apply other elections as applicable as additional changes in the market occur.

Financial Instruments- Credit Loss Amendments

On January 1, 2020, Piedmont adopted ASU No. 2016-13, Financial Instruments—Credit Losses (Topic 326), Measurement of Credit Losses on Financial Instruments, as well as ASU No. 2019-04, Codification Improvements to Topic 326, Financial Instruments - Credit Losses, Topic 815, Derivatives and Hedging, and Topic 825, Financial Instruments, and ASU No. 2019-05, Financial Instruments- Credit Losses: Targeted Transition Relief (collectively the "Credit Loss Amendments"). The provisions of the Credit Loss Amendments replace the "incurred loss" approach with an "expected loss" model for impairing trade and other receivables, held-to-maturity debt securities, net investment in leases, and off-balance-sheet credit exposures, which will generally result in earlier recognition of allowances for credit losses. However, the Financial Accounting Standards Board (the "FASB") also issued ASU No. 2018-19 Codification Improvements to Topic 326, Financial Instruments - Credit

Losses, which is effective concurrent with the Credit Loss Amendments, and excludes receivables arising from operating leases from the scope of the Credit Loss Amendments and affirms that such receivables should be evaluated for collectibility as prescribed by ASC 842 Leases. As substantially all of Piedmont's receivables are operating lease receivables there was no material impact to Piedmont's accompanying consolidated financial statements or disclosures as a result of adoption of the Credit Loss Amendments.

During the nine months ended September 30, 2020, the FASB issued a Staff Q&A on Topic 842 and Topic 840 (lease accounting guidance): Accounting for lease concessions related to the effects of the COVID-19 pandemic. Generally, changes to payment terms not contemplated by the lease contract should be accounted for under Topic 842 as a lease modification. The FASB staff has provided relief from this modification guidance through an accounting policy election, provided that changes to the payment terms do not result in a substantial increase in the rights of either the lessee or the lessor under the lease. Piedmont has elected not to apply the relief provided by the FASB Staff, and has instead accounted for all rent relief agreements as result of COVID-19 as lease modifications. See further details concerning rent relief agreements with Piedmont's tenants in Note 7 below.

Reclassifications

Certain prior period amounts presented in the accompanying consolidated balance sheets have been reclassified as of December 31, 2019 to conform to the current period financial statement presentation related to the 1901 Market Street building, which was classified as held for sale as of March 31, 2020, and sold on June 25, 2020. (see Note 8).

Risk Management Objective of Using Derivatives

In addition to operational risks which arise in the normal course of business, Piedmont is exposed to economic risks such as interest rate, liquidity, and credit risk. In certain situations, Piedmont has entered into derivative financial instruments such as interest rate swap agreements and other similar agreements to manage interest rate risk exposure arising from current or future variable rate debt transactions. Interest rate swap agreements involve the receipt or payment of future known and uncertain cash amounts, the value of which are determined by interest rates. Piedmont’s objective in using interest rate derivatives is to add stability to interest expense and to manage its exposure to interest rate movements.

- Definition

Disclosure of accounting policy for income taxes, which may include its accounting policies for recognizing and measuring deferred tax assets and liabilities and related valuation allowances, recognizing investment tax credits, operating loss carryforwards, tax credit carryforwards, and other carryforwards, methodologies for determining its effective income tax rate and the characterization of interest and penalties in the financial statements.

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+ Details