Defined Contribution Plan	3 Months Ended
Mar. 31, 2022
Compensation And Retirement Disclosure [Abstract]
Defined Contribution Plan	20. DEFINED CONTRIBUTION PLAN On January 1, 2014, the Company established the Montrose Environmental Group 401(k) Savings Plan (the “401(k) Savings Plan”). As of March 31, 2022, and December 31, 2021, plan participants may defer up to 85.0% of their eligible wages for the year, up to the Internal Revenue Service dollar limit and catch-up contribution allowed by law. Prior to May 22, 2020, the Company provided employer matching contributions equal to 100.0% of the first 3.0% of the participant’s compensation and 50.0% of the participant’s elective deferrals that exceed 3.0% but do not exceed 4.0% of the participant’s compensation. Beginning on May 22, 2020, the Company temporarily ceased making employer contributions. Employer contributions were reinstated beginning on April 23, 2021. Employer contributions under the 401(k) Savings Plan were $1.7 million and zero for the three months ended March 31, 2022 and March 31, 2021, respectively, and are included within selling, general, and administrative expense on the unaudited condensed consolidated statements of operations.

Defined Contribution Plan

3 Months Ended

Mar. 31, 2022

Compensation And Retirement Disclosure [Abstract]

20. DEFINED CONTRIBUTION PLAN

On January 1, 2014, the Company established the Montrose Environmental Group 401(k) Savings Plan (the “401(k) Savings Plan”). As of March 31, 2022, and December 31, 2021, plan participants may defer up to 85.0% of their eligible wages for the year, up to the Internal Revenue Service dollar limit and catch-up contribution allowed by law. Prior to May 22, 2020, the Company provided employer matching contributions equal to 100.0% of the first 3.0% of the participant’s compensation and 50.0% of the participant’s elective deferrals that exceed 3.0% but do not exceed 4.0% of the participant’s compensation. Beginning on May 22, 2020, the Company temporarily ceased making employer contributions. Employer contributions were reinstated beginning on April 23, 2021. Employer contributions under the 401(k) Savings Plan were $1.7 million and zero for the three months ended March 31, 2022 and March 31, 2021, respectively, and are included within selling, general, and administrative expense on the unaudited condensed consolidated statements of operations.