Basis of Presentation and Nature of Operations	12 Months Ended
Dec. 31, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Basis of Presentation and Nature of Operations	NOTE 1 - BASIS OF PRESENTATION AND NATURE OF OPERATIONS Basis of Presentation and Nature of Operations 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. All significant intercompany transactions and balances have been eliminated. Nature of Operations The Company provides professional services and technology-based solutions to government and commercial clients, including management, technology, and policy consulting and implementation services, in the areas of energy, environment, and infrastructure; health, education, and social programs; safety and security; and consumer and financial. The Company offers a full range of services to these clients throughout the entire life cycle of a policy, program, project, or initiative, from research and analysis and assessment and advice to design and implementation of programs and technology-based solutions, and the provision of engagement services and programs. The Company’s major clients are U.S. federal government departments and agencies, most significantly the Department of Health and Human Services, Department of State and Department of Defense. The Company also serves U.S. state (including territories) and local government departments and agencies, international governments, and commercial clients worldwide. Commercial clients include airlines, airports, electric and gas utilities, oil companies, banks and other financial services companies, transportation, travel and hospitality firms, non-profits/associations, law firms, manufacturing firms, retail chains, and distribution companies. The term “federal” or “federal government” refers to the U.S. federal government, and “state and local” or “state and local government” refers to U.S. state (including territories) and local governments, unless otherwise indicated. The Company, incorporated in Delaware, is headquartered in Fairfax, Virginia. It maintains offices throughout the world, including over 65 offices in the U.S. and U.S. territories and more than 15 offices in key markets outside the U.S., including offices in the United Kingdom, Belgium, China, India and Canada. Reclassifications Certain amounts in the 2017 and 2016 consolidated financial statements have been reclassified to conform to the current year presentation. As a result of the adoption of Accounting Standard Update (“ASU”) 2014-09, Revenue from Contracts with Customers (Topic 606), the Company presented balances, titled contract assets and contract liabilities, within the consolidated balance sheet as well as the net impact of changes in these balances within the consolidated statement of cash flows. The Company reclassified comparable balances within the December 31, 2017 consolidated balance sheet as well as the impact of changes in these balances within the 2017 and 2016 consolidated statement of cash flows in order to enhance comparability. Any other reclassifications were immaterial to the financial statements taken as a whole.

Basis of Presentation and Nature of Operations

12 Months Ended

Dec. 31, 2018

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Basis of Presentation and Nature of Operations

NOTE 1 - BASIS OF PRESENTATION AND NATURE OF OPERATIONS

Basis of Presentation and Nature of Operations

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. All significant intercompany transactions and balances have been eliminated.

Nature of Operations

The Company provides professional services and technology-based solutions to government and commercial clients, including management, technology, and policy consulting and implementation services, in the areas of energy, environment, and infrastructure; health, education, and social programs; safety and security; and consumer and financial. The Company offers a full range of services to these clients throughout the entire life cycle of a policy, program, project, or initiative, from research and analysis and assessment and advice to design and implementation of programs and technology-based solutions, and the provision of engagement services and programs.

The Company’s major clients are U.S. federal government departments and agencies, most significantly the Department of Health and Human Services, Department of State and Department of Defense. The Company also serves U.S. state (including territories) and local government departments and agencies, international governments, and commercial clients worldwide. Commercial clients include airlines, airports, electric and gas utilities, oil companies, banks and other financial services companies, transportation, travel and hospitality firms, non-profits/associations, law firms, manufacturing firms, retail chains, and distribution companies. The term “federal” or “federal government” refers to the U.S. federal government, and “state and local” or “state and local government” refers to U.S. state (including territories) and local governments, unless otherwise indicated.

The Company, incorporated in Delaware, is headquartered in Fairfax, Virginia. It maintains offices throughout the world, including over 65 offices in the U.S. and U.S. territories and more than 15 offices in key markets outside the U.S., including offices in the United Kingdom, Belgium, China, India and Canada.

Reclassifications

Certain amounts in the 2017 and 2016 consolidated financial statements have been reclassified to conform to the current year presentation.

As a result of the adoption of Accounting Standard Update (“ASU”) 2014-09, Revenue from Contracts with Customers (Topic 606), the Company presented balances, titled contract assets and contract liabilities, within the consolidated balance sheet as well as the net impact of changes in these balances within the consolidated statement of cash flows. The Company reclassified comparable balances within the December 31, 2017 consolidated balance sheet as well as the impact of changes in these balances within the 2017 and 2016 consolidated statement of cash flows in order to enhance comparability. Any other reclassifications were immaterial to the financial statements taken as a whole.