Basis of Presentation and Nature of Operations (Policies)	9 Months Ended
Sep. 30, 2020
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying consolidated financial statements include the accounts of ICF International, Inc. and its subsidiaries (collectively, the “Company”), and have been prepared in accordance with United States (“U.S.”) generally accepted accounting principles (“U.S. GAAP”). All significant 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 assets and 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, contingent consideration related to business acquisitions, impairment of goodwill and long-lived assets, accrued liabilities, revenue recognition and 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.
Reclassifications	Reclassifications As part of an amendment to the Credit Facility, as defined in Note 4 “Long-term Debt” below, the Company currently has both a term loan and a revolving debt facility within its Credit Facility. Previously, the unamortized debt issuance costs were included within Other assets in accordance with U.S. GAAP. The Company has reclassified unamortized debt issuance costs as of December 31, 2019 as Long-term debt for consistency of presentation.
Goodwill	Goodwill The Company tests for impairment, at a minimum, on an annual basis or earlier when certain events or changes in circumstances indicate that goodwill may more likely than not be impaired. If there are significant decreases in its stock price for a sustained period or other unfavorable factors, the Company may be required to perform a goodwill impairment assessment, which may result in a recognition of goodwill impairment that could be material to the consolidated financial statements.
Long-Lived Assets	Long-Lived Assets The Company reviews its long-lived assets, including property and equipment and amortizable intangible assets, for impairment whenever events or changes in circumstances indicate that the carrying amounts of the assets may not be fully recoverable. If the total of the expected undiscounted future net cash flows is less than the carrying amount of the long-lived asset being evaluated, a loss is recognized for any excess of the carrying amount over the fair value of the asset. The Company recognized impairment expense, included in indirect and selling expenses, of $1.7 million in the second quarter of 2019 related to intangible assets associated with a historical business acquisition. There was no impairment recognized during the period ended September 30, 2020.
Leases	Leases The Company determines if an arrangement is a lease at inception. Operating leases are included in operating lease right-of-use (“ROU”) assets and operating lease liabilities (current and non-current) on the consolidated balance sheets. Operating lease ROU assets and operating lease liabilities are recognized based on the present value of the future minimum lease payments as of the commencement date. Since most lease agreements do not provide an implicit rate, the Company uses its incremental borrowing rate as of the commencement date in estimating the present value of future payments. The operating lease ROU asset is based on the present value of future lease payments and includes impacts from lease incentives and initial costs incurred to obtain the lease. Lease terms, for the purposes of determining each lease’s present value, include options to extend or terminate the lease if it is reasonably certain and economically reasonable that the Company will exercise that option. Lease expense for minimum lease payments is recognized on a straight-line basis over the lease term. The Company uses leases to obtain use of a variety of different resources, including those for the use of facilities or equipment. These agreements may contain both lease and non-lease components, which are generally accounted for separately. For equipment leases (including copier leases), the Company accounts for the lease component, as well as insignificant non-lease components, as a single lease component and does not recognize ROU assets and liabilities for leases with a term not greater than twelve months.
Recent Accounting Pronouncements	Recent Accounting Pronouncements Recent Accounting Pronouncements Adopted Implementation Costs Incurred in a Cloud Computing Arrangement That is a Service Contract In August 2018, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2018-15, Intangibles – Goodwill and Other – Internal-Use Software (Subtopic 350-40). The standard aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is considered a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. The standard also requires the entity to expense the capitalized implementation costs of a hosting arrangement over the term of the hosting arrangement and present the expense related to the capitalized implementation costs in the same line item in the statement of income as the fees associated with the hosting arrangement. The Company adopted the standard in the first quarter of 2020 and the standard was implemented using the prospective method. The Company’s adoption of ASU 2018-15 did not have a material impact on the consolidated financial statements. Measurement of Credit Losses on Financial Instruments In June 2016, the FASB issued ASU 2016-13, Financial Instruments – Credit Losses (Topic 326) – Measurement of Credit Losses on Financial Instruments. The standard, as amended, requires companies to measure credit losses by using a methodology that reflects the expected credit losses based on historical information, current economic conditions, and reasonable and supportable information. The Company adopted the standard in the first quarter of 2020 utilizing a modified-retrospective transition approach that required a cumulative-effect adjustment of $0.5 million to the opening retained earnings in the consolidated statement of stockholders’ equity as of the date of the adoption. Recent Accounting Pronouncements Not Yet Adopted Reference Rate Reform In March 2020, FASB issued 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 the 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. The Company can elect to not apply certain modification accounting requirements to contracts affected by reference rate reform, if certain criteria are met. Also, the Company can elect various optional expedients that would allow for the Company to continue to apply hedge accounting for hedging relationships affected by reference rate reform, if certain criteria are met, This guidance is effective beginning on March 12, 2020, and the Company may elect to apply the amendments prospectively through December 31, 2022. The Company is currently evaluating the impact this guidance may have on its consolidated financial statements.

Basis of Presentation and Nature of Operations (Policies)

9 Months Ended

Sep. 30, 2020

The accompanying consolidated financial statements include the accounts of ICF International, Inc. and its subsidiaries (collectively, the “Company”), and have been prepared in accordance with United States (“U.S.”) generally accepted accounting principles (“U.S. GAAP”). All significant 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 assets and 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, contingent consideration related to business acquisitions, impairment of goodwill and long-lived assets, accrued liabilities, revenue recognition and 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.

Reclassifications

As part of an amendment to the Credit Facility, as defined in Note 4 “Long-term Debt” below, the Company currently has both a term loan and a revolving debt facility within its Credit Facility. Previously, the unamortized debt issuance costs were included within Other assets in accordance with U.S. GAAP. The Company has reclassified unamortized debt issuance costs as of December 31, 2019 as Long-term debt for consistency of presentation.

Goodwill

The Company tests for impairment, at a minimum, on an annual basis or earlier when certain events or changes in circumstances indicate that goodwill may more likely than not be impaired. If there are significant decreases in its stock price for a sustained period or other unfavorable factors, the Company may be required to perform a goodwill impairment assessment, which may result in a recognition of goodwill impairment that could be material to the consolidated financial statements.

Long-Lived Assets

The Company reviews its long-lived assets, including property and equipment and amortizable intangible assets, for impairment whenever events or changes in circumstances indicate that the carrying amounts of the assets may not be fully recoverable. If the total of the expected undiscounted future net cash flows is less than the carrying amount of the long-lived asset being evaluated, a loss is recognized for any excess of the carrying amount over the fair value of the asset. The Company recognized impairment expense, included in indirect and selling expenses, of $1.7 million in the second quarter of 2019 related to intangible assets associated with a historical business acquisition. There was no impairment recognized during the period ended September 30, 2020.

Leases

The Company determines if an arrangement is a lease at inception. Operating leases are included in operating lease right-of-use (“ROU”) assets and operating lease liabilities (current and non-current) on the consolidated balance sheets. Operating lease ROU assets and operating lease liabilities are recognized based on the present value of the future minimum lease payments as of the commencement date. Since most lease agreements do not provide an implicit rate, the Company uses its incremental borrowing rate as of the commencement date in estimating the present value of future payments. The operating lease ROU asset is based on the present value of future lease payments and includes impacts from lease incentives and initial costs incurred to obtain the lease. Lease terms, for the purposes of determining each lease’s present value, include options to extend or terminate the lease if it is reasonably certain and economically reasonable that the Company will exercise that option. Lease expense for minimum lease payments is recognized on a straight-line basis over the lease term.

The Company uses leases to obtain use of a variety of different resources, including those for the use of facilities or equipment. These agreements may contain both lease and non-lease components, which are generally accounted for separately. For equipment leases (including copier leases), the Company accounts for the lease component, as well as insignificant non-lease components, as a single lease component and does not recognize ROU assets and liabilities for leases with a term not greater than twelve months.

Recent Accounting Pronouncements

Recent Accounting Pronouncements Adopted

Implementation Costs Incurred in a Cloud Computing Arrangement That is a Service Contract

In August 2018, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2018-15, Intangibles – Goodwill and Other – Internal-Use Software (Subtopic 350-40). The standard aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is considered a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. The standard also requires the entity to expense the capitalized implementation costs of a hosting arrangement over the term of the hosting arrangement and present the expense related to the capitalized implementation costs in the same line item in the statement of income as the fees associated with the hosting arrangement. The Company adopted the standard in the first quarter of 2020 and the standard was implemented using the prospective method. The Company’s adoption of ASU 2018-15 did not have a material impact on the consolidated financial statements.

Measurement of Credit Losses on Financial Instruments

In June 2016, the FASB issued ASU 2016-13, Financial Instruments – Credit Losses (Topic 326) – Measurement of Credit Losses on Financial Instruments. The standard, as amended, requires companies to measure credit losses by using a methodology that reflects the expected credit losses based on historical information, current economic conditions, and reasonable and supportable information. The Company adopted the standard in the first quarter of 2020 utilizing a modified-retrospective transition approach that required a cumulative-effect adjustment of $0.5 million to the opening retained earnings in the consolidated statement of stockholders’ equity as of the date of the adoption.

Recent Accounting Pronouncements Not Yet Adopted

Reference Rate Reform

In March 2020, FASB issued 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 the 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. The Company can elect to not apply certain modification accounting requirements to contracts affected by reference rate reform, if certain criteria are met. Also, the Company can elect various optional expedients that would allow for the Company to continue to apply hedge accounting for hedging relationships affected by reference rate reform, if certain criteria are met, This guidance is effective beginning on March 12, 2020, and the Company may elect to apply the amendments prospectively through December 31, 2022. The Company is currently evaluating the impact this guidance may have on its consolidated financial statements.