Basis of Presentation and Principles of Consolidation (Policies)	3 Months Ended
Mar. 31, 2020
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, 2019. 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 include the accounts of Parsons Corporation and its subsidiaries and affiliates with 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, 2019, 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.
New Accounting Pronouncements	In the first quarter of 2020, the Company adopted Accounting Standards Update (“ASU”) 2016-13, “Measurement of Credit Losses on Financial Instruments.” The amendments in ASU 2016-13 replace 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 Company’s consolidated financial statements. In December 2019, the Financial Accounting Standards Board (“FASB”) issued 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 for those entities that fall within the scope of the standard. 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. ASU 2019-12 is effective for fiscal years beginning after December 15, 2020, with early adoption permitted. The Company is evaluating the impact of ASU 2019-12 on its 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 11 years, some of which may include options to extend the leases for up to seven years, and some of which may include options to terminate the leases up to the eighth year.

Basis of Presentation and Principles of Consolidation (Policies)

3 Months Ended

Mar. 31, 2020

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, 2019.

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 include the accounts of Parsons Corporation and its subsidiaries and affiliates with 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, 2019, 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.

New Accounting Pronouncements

In the first quarter of 2020, the Company adopted Accounting Standards Update (“ASU”) 2016-13, “Measurement of Credit Losses on Financial Instruments.” The amendments in ASU 2016-13 replace 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 Company’s consolidated financial statements.

In December 2019, the Financial Accounting Standards Board (“FASB”) issued 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 for those entities that fall within the scope of the standard. 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. ASU 2019-12 is effective for fiscal years beginning after December 15, 2020, with early adoption permitted. The Company is evaluating the impact of ASU 2019-12 on its 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 11 years, some of which may include options to extend the leases for up to seven years, and some of which may include options to terminate the leases up to the eighth year.