Description of the Business and Basis of Presentation	12 Months Ended
Dec. 31, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Description of the Business and Basis of Presentation	1. DESCRIPTION OF THE BUSINESS AND BASIS OF PRESENTATION Description of the Business—Montrose Environmental Group, Inc. (“Montrose” or the “Company”) is a corporation formed on November 2013, under the laws of the State of Delaware. The Company has approximately 80 offices across the United States, Canada and Australia and approximately 2,500 employees as of December 31, 2021. Montrose is an environmental services company serving the recurring environmental needs of a diverse client base, including Fortune 500 companies and Federal, State and local governments through the following three segments: Assessment, Permitting and Response—Through its Assessment, Permitting and Response segment, Montrose provides scientific advisory and consulting services to support environmental assessments, environmental emergency response, and environmental audits and permits for current operations, facility upgrades, new projects, decommissioning projects and development projects. The Company’s technical advisory and consulting offerings include regulatory compliance support and planning, environmental, ecosystem and toxicological assessments and support during responses to environmental disruption. Montrose helps clients navigate regulations at the local, state, provincial and federal levels. Measurement and Analysis—Through its Measurement and Analysis segment, Montrose’s teams test and analyze air, water and soil to determine concentrations of contaminants as well as the toxicological impact of contaminants on flora, fauna and human health. Montrose’s offerings include source and ambient air testing and monitoring, leak detection and repair (“LDAR”) and advanced analytical laboratory services such as air, storm water, wastewater and drinking water analysis. Remediation and Reuse—Through its Remediation and Reuse segment, Montrose provides clients with engineering, design, implementation and operations and maintenance services, primarily to treat contaminated water, remove contaminants from soil or create biogas from waste. The Company does not own the properties or facilities at which it implements these projects or the underlying liabilities, nor does it own material amounts of the equipment used in projects; instead, the Company assists clients in designing solutions, managing projects and mitigating their environmental risks and liabilities at their locations. Initial Public Offering—On July 27, 2020, the Company completed its initial public offering (“IPO”) of common stock, in which it sold 11,500,000 shares, including 1,500,000 shares issued pursuant to the underwriters full exercise on July 24, 2020 of the underwriters’ option to purchase additional shares, at a price to the public of $15.00 per share, resulting in net proceeds to the Company of approximately $161.3 million after deducting underwriting discounts of $11.2 million. Additionally, the Company offset $4.4 million of deferred IPO costs against IPO proceeds recorded to additional paid in capital. These deferred IPO costs were directly attributable to the IPO offering in accordance with Staff Accounting Bulletin Topic 5: Miscellaneous Accounting. The Company’s common stock began trading on the New York Stock Exchange on July 23, 2020. Follow-on Offering—On October 1, 2021, the Company completed a follow-on offering of common stock, in which it sold 2,875,000 shares, including 375,000 shares issued pursuant to the underwriters full exercise on October 5, 2021 of the underwriters’ option to purchase additional shares, at a price to the public of $62.00 per share, resulting in net proceeds to the Company of approximately $169.8 million after deducting underwriting discounts of $8.5 million. Additionally, the Company offset $0.6 million of deferred follow-on offering costs against follow-on proceeds recorded to additional paid in capital. These deferred follow-on offering costs were directly attributable to the follow-on offering in accordance with Staff Accounting Bulletin Topic 5: Miscellaneous Accounting. Basis of Presentation—The accompanying consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States (“GAAP”).

Description of the Business and Basis of Presentation

12 Months Ended

Dec. 31, 2021

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Description of the Business and Basis of Presentation

1. DESCRIPTION OF THE BUSINESS AND BASIS OF PRESENTATION

Description of the Business—Montrose Environmental Group, Inc. (“Montrose” or the “Company”) is a corporation formed on November 2013, under the laws of the State of Delaware. The Company has approximately 80 offices across the United States, Canada and Australia and approximately 2,500 employees as of December 31, 2021.

Montrose is an environmental services company serving the recurring environmental needs of a diverse client base, including Fortune 500 companies and Federal, State and local governments through the following three segments:

Assessment, Permitting and Response—Through its Assessment, Permitting and Response segment, Montrose provides scientific advisory and consulting services to support environmental assessments, environmental emergency response, and environmental audits and permits for current operations, facility upgrades, new projects, decommissioning projects and development projects. The Company’s technical advisory and consulting offerings include regulatory compliance support and planning, environmental, ecosystem and toxicological assessments and support during responses to environmental disruption. Montrose helps clients navigate regulations at the local, state, provincial and federal levels.

Measurement and Analysis—Through its Measurement and Analysis segment, Montrose’s teams test and analyze air, water and soil to determine concentrations of contaminants as well as the toxicological impact of contaminants on flora, fauna and human health. Montrose’s offerings include source and ambient air testing and monitoring, leak detection and repair (“LDAR”) and advanced analytical laboratory services such as air, storm water, wastewater and drinking water analysis.

Remediation and Reuse—Through its Remediation and Reuse segment, Montrose provides clients with engineering, design, implementation and operations and maintenance services, primarily to treat contaminated water, remove contaminants from soil or create biogas from waste. The Company does not own the properties or facilities at which it implements these projects or the underlying liabilities, nor does it own material amounts of the equipment used in projects; instead, the Company assists clients in designing solutions, managing projects and mitigating their environmental risks and liabilities at their locations.

Initial Public Offering—On July 27, 2020, the Company completed its initial public offering (“IPO”) of common stock, in which it sold 11,500,000 shares, including 1,500,000 shares issued pursuant to the underwriters full exercise on July 24, 2020 of the underwriters’ option to purchase additional shares, at a price to the public of $15.00 per share, resulting in net proceeds to the Company of approximately $161.3 million after deducting underwriting discounts of $11.2 million. Additionally, the Company offset $4.4 million of deferred IPO costs against IPO proceeds recorded to additional paid in capital. These deferred IPO costs were directly attributable to the IPO offering in accordance with Staff Accounting Bulletin Topic 5: Miscellaneous Accounting. The Company’s common stock began trading on the New York Stock Exchange on July 23, 2020.

Follow-on Offering—On October 1, 2021, the Company completed a follow-on offering of common stock, in which it sold 2,875,000 shares, including 375,000 shares issued pursuant to the underwriters full exercise on October 5, 2021 of the underwriters’ option to purchase additional shares, at a price to the public of $62.00 per share, resulting in net proceeds to the Company of approximately $169.8 million after deducting underwriting discounts of $8.5 million. Additionally, the Company offset $0.6 million of deferred follow-on offering costs against follow-on proceeds recorded to additional paid in capital. These deferred follow-on offering costs were directly attributable to the follow-on offering in accordance with Staff Accounting Bulletin Topic 5: Miscellaneous Accounting.

Basis of Presentation—The accompanying consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States (“GAAP”).