Basis of Presentation and Nature of Operations (Policies)	3 Months Ended
Mar. 31, 2023
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying consolidated financial statements include the accounts of ICF International, Inc. (“ICFI”) and its principal subsidiary, ICF Consulting Group, Inc. (“Consulting,” and together with ICFI, the “Company”), and have been prepared in accordance with United States (“U.S.”) generally accepted accounting principles (“U.S. GAAP”). Consulting is a wholly owned subsidiary of ICFI. ICFI is a holding company with no operations or assets other than its investment in the common stock of Consulting. All other subsidiaries of the Company are wholly owned by Consulting. Material intercompany transactions and balances have been eliminated.
Use of Estimates	Use of Estimates The preparation of consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent liabilities at the date of the consolidated financial statements, and the reported amounts of revenue and expenses during the reporting periods. Areas of the consolidated financial statements where estimates may have the most significant effect include contractual and regulatory reserves, valuation and lives of tangible and intangible assets, impairment of goodwill and long-lived assets, accrued liabilities, revenue recognition (including estimates of variable considerations in determining the total contract price and allocation of performance obligations), the remaining costs to complete fixed-price contracts, bonus and other incentive compensation, stock-based compensation, reserves for tax benefits and valuation allowances on deferred tax assets, provisions for income taxes, collectability of receivables, and loss accruals for litigation. Actual results experienced by the Company may differ from management's estimates.
Recent Accounting Pronouncements	Recent Accounting Pronouncements Recent Accounting Pronouncements Not Yet Adopted Reference Rate Reform In March 2020, the Financial Accounting Standards Board issued Accounting Standards Update (“ASU”) 2020-04, Facilitation of the Effects of Reference Rate Reform on Financial Reporting. The standard is intended to provide temporary optional expedients and exceptions to the U.S. GAAP guidance on contract modifications and hedge accounting to ease accounting and financial reporting burdens related to the expected market transition from the London Interbank Offered Rate (“LIBOR”) and other interbank offered rates to alternative reference rates. The provisions of this ASU are elective and apply to all entities, subject to meeting certain criteria, that have debt or hedging contracts, among other contracts, that reference LIBOR or another reference rate expected to be discontinued because of reference rate reform. Entities can elect to not apply certain modification accounting requirements to contracts affected by reference rate reform if certain criteria are met. Also, entities can elect various optional expedients that would allow it to continue to apply hedge accounting for hedging relationships affected by reference rate reform if certain criteria are met. This guidance was effective beginning on March 12, 2020 and entities may elect to apply the amendments prospectively through December 31, 2022, the sunset date. In December 2022, the FASB issued ASU 2022-06 Reference Rate Reform (Topic 848): Deferral of the Sunset Date of Topic 848 that extended the sunset date from December 31, 2022 to December 31, 2024. As of March 31, 2023, the Company has one interest rate swap contract with a variable interest rate that references LIBOR. The contract expires on August 31, 2023.
Reclassification	Reclassification Certain immaterial amounts in the consolidated statements of comprehensive income have been reclassified to conform to the current year’s presentation. To be consistent with the current presentation of interest, net, the Company reclassified $0.1 million in interest income for the three months ended March 31, 2022 from “Other expense” to “Interest, net”.

Basis of Presentation and Nature of Operations (Policies)

3 Months Ended

Mar. 31, 2023

The accompanying consolidated financial statements include the accounts of ICF International, Inc. (“ICFI”) and its principal subsidiary, ICF Consulting Group, Inc. (“Consulting,” and together with ICFI, the “Company”), and have been prepared in accordance with United States (“U.S.”) generally accepted accounting principles (“U.S. GAAP”). Consulting is a wholly owned subsidiary of ICFI. ICFI is a holding company with no operations or assets other than its investment in the common stock of Consulting. All other subsidiaries of the Company are wholly owned by Consulting. Material intercompany transactions and balances have been eliminated.

Use of Estimates

The preparation of consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent liabilities at the date of the consolidated financial statements, and the reported amounts of revenue and expenses during the reporting periods. Areas of the consolidated financial statements where estimates may have the most significant effect include contractual and regulatory reserves, valuation and lives of tangible and intangible assets, impairment of goodwill and long-lived assets, accrued liabilities, revenue recognition (including estimates of variable considerations in determining the total contract price and allocation of performance obligations), the remaining costs to complete fixed-price contracts, bonus and other incentive compensation, stock-based compensation, reserves for tax benefits and valuation allowances on deferred tax assets, provisions for income taxes, collectability of receivables, and loss accruals for litigation. Actual results experienced by the Company may differ from management's estimates.

Recent Accounting Pronouncements

Recent Accounting Pronouncements Not Yet Adopted

Reference Rate Reform

In March 2020, the Financial Accounting Standards Board issued Accounting Standards Update (“ASU”) 2020-04, Facilitation of the Effects of Reference Rate Reform on Financial Reporting. The standard is intended to provide temporary optional expedients and exceptions to the U.S. GAAP guidance on contract modifications and hedge accounting to ease accounting and financial reporting burdens related to the expected market transition from the London Interbank Offered Rate (“LIBOR”) and other interbank offered rates to alternative reference rates. The provisions of this ASU are elective and apply to all entities, subject to meeting certain criteria, that have debt or hedging contracts, among other contracts, that reference LIBOR or another reference rate expected to be discontinued because of reference rate reform. Entities can elect to not apply certain modification accounting requirements to contracts affected by reference rate reform if certain criteria are met. Also, entities can elect various optional expedients that would allow it to continue to apply hedge accounting for hedging relationships affected by reference rate reform if certain criteria are met. This guidance was effective beginning on March 12, 2020 and entities may elect to apply the amendments prospectively through December 31, 2022, the sunset date. In December 2022, the FASB issued ASU 2022-06 Reference Rate Reform (Topic 848): Deferral of the Sunset Date of Topic 848 that extended the sunset date from December 31, 2022 to December 31, 2024.

As of March 31, 2023, the Company has one interest rate swap contract with a variable interest rate that references LIBOR. The contract expires on August 31, 2023.

Reclassification

Certain immaterial amounts in the consolidated statements of comprehensive income have been reclassified to conform to the current year’s presentation. To be consistent with the current presentation of interest, net, the Company reclassified $0.1 million in interest income for the three months ended March 31, 2022 from “Other expense” to “Interest, net”.