Basis of Presentation and Principles of Consolidation (Policies)	6 Months Ended
Jun. 30, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Basis of Presentation and Principles of Consolidation	The accompanying unaudited consolidated financial statements and related notes of the Company have been prepared in accordance with generally accepted accounting principles in the United States of America ("GAAP") and pursuant to the interim period reporting requirements of Form 10-Q. They do not include all of the information and footnotes required by GAAP for complete financial statements and, therefore, should be read in conjunction with our consolidated financial statements and the notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2020. In the opinion of management, the consolidated financial statements reflect all normal recurring adjustments necessary for a fair statement of the financial position, results of operations and cash flows for the interim periods presented. The results of operations and cash flows for any interim period are not necessarily indicative of results for the full year or for future years. This Quarterly Report on Form 10-Q includes the accounts of Parsons Corporation and its subsidiaries and affiliates which it controls. Interests in joint ventures that are controlled by the Company, or for which the Company is otherwise deemed to be the primary beneficiary, are consolidated. For joint ventures in which the Company does not have a controlling interest, but exerts a significant influence, the Company applies the equity method of accounting (see “Note 14 – Investments in and Advances to Joint Ventures" for further discussion). Intercompany accounts and transactions are eliminated in consolidation.
Use of Estimates	Use of Estimates The preparation of the consolidated financial statements in accordance with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual amounts could differ from those estimates. The Company’s most significant estimates and judgments involve revenue recognition with respect to the determination of the costs to complete contracts and transaction price; determination of self-insurance reserves; useful lives of property and equipment and intangible assets; calculation of allowance for doubtful accounts; valuation of deferred income tax assets and uncertain tax positions, among others. Please see “Management’s Discussion and Analysis of Financial Condition and Results of Operations—Critical Accounting Policies and Estimates” and “Note 2—Summary of Significant Accounting Polices” in the notes to our consolidated financial statements included in the Company’s Form 10-K for the year ended December 31, 2020, for a discussion of the significant estimates and assumptions affecting our consolidated financial statements. Estimates of costs to complete contracts are continually evaluated as work progresses and are revised when necessary. When a change in estimate is determined to have an impact on contract profit, the Company records a positive or negative adjustment to the consolidated statement of income.
Employee Stock Purchase Plan	Employee Stock Purchase Plan During the second quarter of fiscal 2020, initial purchases of the Company’s common Stock were made under the Parsons Employee Stock Purchase Program (“ESPP”). Under the ESPP, eligible employees who elect to participate are granted the right to purchase shares of the common stock of Parsons at a discount that is limited to 5% of the per-share market value on the day shares are sold to employees. Purchases of common stock under the ESPP are included in “proceeds from issuance of common stock” in cash flows from financing activities in the Consolidated Statements of Cash Flows.
New Accounting Pronouncements	In the first quarter of 2021, the Company early adopted Accounting Standards Update (“ASU”) ASU 2020-06, Debt – Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging – Contracts in Entity’s Own Equity (Subtopic 815-40) (“ASU 2020-06)”. The update simplifies the accounting for convertible debt instruments and convertible preferred stock by reducing the number of accounting models and limiting the number of embedded conversion features separately recognized from the primary contract. The guidance also includes targeted improvements to the disclosures for convertible instruments and earnings per share. ASU 2020-06 is effective for fiscal years beginning after December 15, 2021, including interim periods within those fiscal years. Early adoption is permitted, but no earlier than fiscal years beginning after December 15, 2020. The Company adopted ASU 2020-06 in the first quarter of 2021 using the modified retrospective method which resulted in a reduction in non-cash interest expense and reclassification of the equity portion of the Convertible Senior Notes to “Long-term debt” on the consolidated balance sheet. In the first quarter of 2021, the Company adopted ASU No. 2019-12, “Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes (“ASU 2019-12”)”. ASU 2019-12 was issued as a means to reduce the complexity of accounting for income taxes. The guidance is to be applied using a prospective method, excluding amendments related to franchise taxes, which should be applied on either a retrospective basis for all periods presented or a modified retrospective basis through a cumulative-effect adjustment to retained earnings as of the beginning of the fiscal year of adoption. The adoption of ASU 2019-12 did not have a material impact on the consolidated financial statements. In the first quarter of 2020, the Company adopted ASU 2016-13, “Measurement of Credit Losses on Financial Instruments.” The amendments in ASU 2016-13 replaced the incurred loss impairment methodology in current practice with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to estimate credit losses. The adoption of ASU 2016-13 did not have a material impact on the consolidated financial statements.
Leases	Leases The Company has operating and finance leases for corporate and project office spaces, vehicles, heavy machinery and office equipment. Our leases have remaining lease terms of one year to 9 years, some of which may include options to extend the leases for up to five years, and some of which may include options to terminate the leases after the third year.

Basis of Presentation and Principles of Consolidation (Policies)

6 Months Ended

Jun. 30, 2021

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Basis of Presentation and Principles of Consolidation

The accompanying unaudited consolidated financial statements and related notes of the Company have been prepared in accordance with generally accepted accounting principles in the United States of America ("GAAP") and pursuant to the interim period reporting requirements of Form 10-Q. They do not include all of the information and footnotes required by GAAP for complete financial statements and, therefore, should be read in conjunction with our consolidated financial statements and the notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2020.

In the opinion of management, the consolidated financial statements reflect all normal recurring adjustments necessary for a fair statement of the financial position, results of operations and cash flows for the interim periods presented. The results of operations and cash flows for any interim period are not necessarily indicative of results for the full year or for future years.

This Quarterly Report on Form 10-Q includes the accounts of Parsons Corporation and its subsidiaries and affiliates which it controls. Interests in joint ventures that are controlled by the Company, or for which the Company is otherwise deemed to be the primary beneficiary, are consolidated. For joint ventures in which the Company does not have a controlling interest, but exerts a significant influence, the Company applies the equity method of accounting (see “Note 14 – Investments in and Advances to Joint Ventures" for further discussion). Intercompany accounts and transactions are eliminated in consolidation.

Use of Estimates

The preparation of the consolidated financial statements in accordance with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual amounts could differ from those estimates. The Company’s most significant estimates and judgments involve revenue recognition with respect to the determination of the costs to complete contracts and transaction price; determination of self-insurance reserves; useful lives of property and equipment and intangible assets; calculation of allowance for doubtful accounts; valuation of deferred income tax assets and uncertain tax positions, among others. Please see “Management’s Discussion and Analysis of Financial Condition and Results of Operations—Critical Accounting Policies and Estimates” and “Note 2—Summary of Significant Accounting Polices” in the notes to our consolidated financial statements included in the Company’s Form 10-K for the year ended December 31, 2020, for a discussion of the significant estimates and assumptions affecting our consolidated financial statements. Estimates of costs to complete contracts are continually evaluated as work progresses and are revised when necessary. When a change in estimate is determined to have an impact on contract profit, the Company records a positive or negative adjustment to the consolidated statement of income.

Employee Stock Purchase Plan

During the second quarter of fiscal 2020, initial purchases of the Company’s common Stock were made under the Parsons Employee Stock Purchase Program (“ESPP”). Under the ESPP, eligible employees who elect to participate are granted the right to purchase shares of the common stock of Parsons at a discount that is limited to 5% of the per-share market value on the day shares are sold to employees. Purchases of common stock under the ESPP are included in

“proceeds from issuance of common stock” in cash flows from financing activities in the Consolidated Statements of Cash Flows.

New Accounting Pronouncements

In the first quarter of 2021, the Company early adopted Accounting Standards Update (“ASU”) ASU 2020-06, Debt – Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging – Contracts in Entity’s Own Equity (Subtopic 815-40) (“ASU 2020-06)”. The update simplifies the accounting for convertible debt instruments and convertible preferred stock by reducing the number of accounting models and limiting the number of embedded conversion features separately recognized from the primary contract. The guidance also includes targeted improvements to the disclosures for convertible instruments and earnings per share. ASU 2020-06 is effective for fiscal years beginning after December 15, 2021, including interim periods within those fiscal years. Early adoption is permitted, but no earlier than fiscal years beginning after December 15, 2020. The Company adopted ASU 2020-06 in the first quarter of 2021 using the modified retrospective method which resulted in a reduction in non-cash interest expense and reclassification of the equity portion of the Convertible Senior Notes to “Long-term debt” on the consolidated balance sheet.

In the first quarter of 2021, the Company adopted ASU No. 2019-12, “Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes (“ASU 2019-12”)”. ASU 2019-12 was issued as a means to reduce the complexity of accounting for income taxes. The guidance is to be applied using a prospective method, excluding amendments related to franchise taxes, which should be applied on either a retrospective basis for all periods presented or a modified retrospective basis through a cumulative-effect adjustment to retained earnings as of the beginning of the fiscal year of adoption. The adoption of ASU 2019-12 did not have a material impact on the consolidated financial statements.

In the first quarter of 2020, the Company adopted ASU 2016-13, “Measurement of Credit Losses on Financial Instruments.” The amendments in ASU 2016-13 replaced the incurred loss impairment methodology in current practice with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to estimate credit losses. The adoption of ASU 2016-13 did not have a material impact on the consolidated financial statements.

Leases

The Company has operating and finance leases for corporate and project office spaces, vehicles, heavy machinery and office equipment. Our leases have remaining lease terms of one year to 9 years, some of which may include options to extend the leases for up to five years, and some of which may include options to terminate the leases after the third year.