Montrose Environmental (MEG) 10-Q 10 May 23 2023 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2023	May 04, 2023
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2023
Document Quarterly Report	true
Document Transition Report	false
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	Q1
Trading Symbol	MEG
Entity Registrant Name	Montrose Environmental Group, Inc.
Entity Central Index Key	0001643615
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		30,078,195
Entity Interactive Data Current	Yes
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity File Number	001-39394
Entity Tax Identification Number	46-4195044
Entity Incorporation State Country Code	DE
Entity Address Address Line1	5120 Northshore Drive
Entity Address City Or Town	North Little Rock
Entity Address State Or Province	AR
Entity Address Postal Zip Code	72118
City Area Code	501
Local Phone Number	900-6400
Security12b Title	Common Stock, par value $0.000004 per share
Security Exchange Name	NYSE

UNAUDITED CONDENSED CONSOLIDATE

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF FINANCIAL POSITION - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
CURRENT ASSETS:
Cash and cash equivalents	$ 76,794	$ 89,828
Accounts receivable—net	85,472	94,711
Contract assets	53,563	52,403
Prepaid and other current assets	15,178	10,986
Total current assets	231,007	247,928
NON-CURRENT ASSETS:
Property and equipment—net	40,685	36,045
Operating lease right-of-use asset—net	31,214	26,038
Finance lease right-of-use asset—net	11,391	9,840
Goodwill	326,498	323,868
Other intangible assets—net	137,271	142,107
Other assets	5,111	6,088
TOTAL ASSETS	783,177	791,914
CURRENT LIABILITIES:
Accounts payable and other accrued liabilities	55,420	63,412
Accrued payroll and benefits	16,352	20,528
Business acquisitions contingent consideration, current	4,734	3,801
Current portion of operating lease liabilities	8,570	7,895
Current portion of finance lease liabilities	4,130	3,775
Current portion of long-term debt	13,125	12,031
Total current liabilities	102,331	111,442
NON-CURRENT LIABILITIES:
Business acquisitions contingent consideration, long-term	3,121	4,454
Other non-current liabilities	3	13
Deferred tax liabilities—net	7,111	5,742
Operating lease liability—net of current portion	24,093	19,437
Finance lease liability—net of current portion	7,507	6,486
Long-term debt—net of deferred financing fees	149,342	152,494
Total liabilities	320,144	325,799
COMMITMENTS AND CONTINGENCIES
STOCKHOLDERS’ EQUITY:
Additional paid-in-capital	504,301	492,676
Accumulated deficit	(194,216)	(179,497)
Accumulated other comprehensive income	20	8
Total stockholders’ equity	310,105	313,187
TOTAL LIABILITIES, CONVERTIBLE AND REDEEMABLE SERIES A-2 PREFERRED STOCK AND STOCKHOLDERS’ EQUITY	783,177	791,914
Conversion Option
NON-CURRENT LIABILITIES:
Conversion option	26,636	25,731
Convertible And Redeemable Series A-2 Preferred Stock
NON-CURRENT LIABILITIES:
REDEEMABLE SERIES PREFERRED STOCK	$ 152,928	$ 152,928

UNAUDITED CONDENSED CONSOLIDA_2

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF FINANCIAL POSITION (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022
Common stock, par value	$ 0.000004	$ 0.000004
Common stock, shares authorized	190,000,000	190,000,000
Common stock, shares issued	29,961,364	29,619,921
Common stock, shares outstanding	29,961,364	29,619,921
Convertible And Redeemable Series A-2 Preferred Stock
Temporary equity, par value	$ 0.0001	$ 0.0001
Temporary equity, shares authorized	17,500	17,500
Temporary equity, shares issued	17,500	17,500
Temporary equity, shares outstanding	17,500	17,500
Temporary equity, aggregate liquidation preference	$ 182.2	$ 182.2

UNAUDITED CONDENSED CONSOLIDA_3

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Income Statement [Abstract]
REVENUES	$ 131,428	$ 134,680
COST OF REVENUES (exclusive of depreciation and amortization shown below)	81,633	88,386
SELLING, GENERAL AND ADMINISTRATIVE EXPENSE	49,613	41,807
FAIR VALUE CHANGES IN BUSINESS ACQUISITIONS CONTINGENCIES	(398)	(21)
DEPRECIATION AND AMORTIZATION	10,555	12,144
LOSS FROM OPERATIONS	(9,975)	(7,636)
OTHER (EXPENSE) INCOME
Other (expense) income	(1,836)	2,461
Interest expense—net	(1,541)	(1,092)
Total other (expense) income - net	(3,377)	1,369
LOSS BEFORE EXPENSE FROM INCOME TAXES	(13,352)	(6,267)
INCOME TAX EXPENSE	1,367	1,269
NET LOSS	(14,719)	(7,536)
EQUITY ADJUSTMENT FROM FOREIGN CURRENCY TRANSLATION	12	81
COMPREHENSIVE LOSS	(14,707)	(7,455)
CONVERTIBLE AND REDEEMABLE SERIES A-2 PREFERRED STOCK DIVIDEND	(4,100)	(4,100)
NET LOSS ATTRIBUTABLE TO COMMON STOCKHOLDERS	$ (18,819)	$ (11,636)
WEIGHTED AVERAGE COMMON SHARES OUTSTANDING - BASIC	29,857	29,662
WEIGHTED AVERAGE COMMON SHARES OUTSTANDING - DILUTED	29,857	29,662
NET LOSS PER SHARE ATTRIBUTABLE TO COMMON STOCKHOLDERS - BASIC	$ (0.63)	$ (0.39)
NET LOSS PER SHARE ATTRIBUTABLE TO COMMON STOCKHOLDERS - DILUTED	$ (0.63)	$ (0.39)

UNAUDITED CONDENSED CONSOLIDA_4

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF CONVERTIBLE AND REDEEMABLE SERIES A-2 PREFERRED STOCK AND STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Convertible And Redeemable Series A-2 Preferred Stock	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Income
Beginning balance at Dec. 31, 2021	$ 316,501			$ 464,143	$ (147,678)	$ 36
Beginning balance, shares at Dec. 31, 2021			29,619,921
Beginning balance at Dec. 31, 2021		$ 152,928
Beginning balance, shares at Dec. 31, 2021		17,500
Net loss	(7,536)				(7,536)
Stock-based compensation	10,425			10,425
Dividend payment to the Series A-2 preferred shareholders	(4,100)	$ (4,100)		(4,100)
Common stock issued	$ 429			429
Common stock issued, shares	55,896		55,896
Accumulated other comprehensive income	$ 45					45
Ending balance at Mar. 31, 2022	315,764			470,897	(155,214)	81
Ending balance, shares at Mar. 31, 2022		17,500
Ending balance at Mar. 31, 2022		$ 152,928
Ending balance, shares at Mar. 31, 2022			29,675,817
Beginning balance at Dec. 31, 2022	313,187			492,676	(179,497)	8
Beginning balance, shares at Dec. 31, 2022			29,746,793
Beginning balance at Dec. 31, 2022		$ 152,928
Beginning balance, shares at Dec. 31, 2022		17,500
Net loss	(14,719)				(14,719)
Stock-based compensation	13,035			13,035
Dividend payment to the Series A-2 preferred shareholders	(4,100)	$ (4,100)		(4,100)
Common stock issued	$ 2,690			2,690
Common stock issued, shares	214,571		214,571
Accumulated other comprehensive income	$ 12					12
Ending balance at Mar. 31, 2023	$ 310,105			$ 504,301	$ (194,216)	$ 20
Ending balance, shares at Mar. 31, 2023		17,500
Ending balance at Mar. 31, 2023		$ 152,928
Ending balance, shares at Mar. 31, 2023			29,961,364

UNAUDITED CONDENSED CONSOLIDA_5

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
OPERATING ACTIVITIES:
Net loss	$ (14,719)	$ (7,536)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Provision (recovery) for bad debt	444	(528)	$ (1,097)
Depreciation and amortization	10,555	12,144
Amortization of right-of-use asset	2,491	2,271
Stock-based compensation expense	13,035	10,425
Fair value changes in financial instruments	1,873	(2,449)
Fair value changes in business acquisition contingencies	(398)	(21)
Deferred income taxes	1,367	1,269
Other	458	143
Changes in operating assets and liabilities—net of acquisitions:
Accounts receivable and contract assets	9,615	10,037
Prepaid expenses and other current assets	(3,363)	(1,776)
Accounts payable and other accrued liabilities	(11,643)	(12,852)
Accrued payroll and benefits	(4,350)	(7,876)
Payment of contingent consideration		(19,457)
Change in operating leases	(2,336)	(2,122)
Net cash provided by (used in) operating activities	3,029	(18,328)
INVESTING ACTIVITIES:
Purchases of property and equipment	(4,134)	(262)
Proprietary software development and other software costs	(638)	(50)
Proceeds from insurance	75	266
Payment of purchase price true ups	(505)	(631)
Cash paid for acquisitions—net of cash acquired	(6,525)	(14,328)
Net cash used in investing activities	(11,727)	(15,005)
FINANCING ACTIVITIES:
Repayment of term loan	(2,188)	(4,375)
Payment of contingent consideration	(27)	(10,543)
Repayment of finance leases	(1,029)	(943)
Proceeds from issuance of common stock for exercised stock options	2,690	429
Dividend payment to the Series A-2 shareholders	(4,100)	(4,100)
Payments of deferred offering costs		(183)
Net cash used in financing activities	(4,654)	(19,715)
CHANGE IN CASH AND CASH EQUIVALENTS	(13,352)	(53,048)
Foreign exchange impact on cash balance	318	98
CASH AND CASH EQUIVALENTS:
Beginning of year	89,828	146,741	146,741
End of period	76,794	93,791	$ 89,828
SUPPLEMENTAL DISCLOSURES OF CASH FLOWS INFORMATION:
Cash paid for interest	1,347	184
Cash paid for income tax	155
SUPPLEMENTAL DISCLOSURES OF NON-CASH INVESTING AND FINANCING ACTIVITIES:
Accrued purchases of property and equipment	3,096	1,144
Property and equipment purchased under finance leases	2,405	512
Acquisitions unpaid contingent consideration	$ 7,855	$ 6,995

Description of the Business and

Description of the Business and Basis of Presentation	3 Months Ended
	Mar. 31, 2023
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 3,000 employees as of March 31, 2023. 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 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, and implementation 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. Basis of Presentation —The unaudited condensed consolidated financial statements include the operations of the Company and its wholly-owned subsidiaries. These unaudited condensed consolidated financial statements are presented in conformity with accounting principles generally accepted in the United States (“U.S. GAAP”) and have been prepared pursuant to the rules and regulations of the U.S. Securities and Exchange Commission (“SEC”) that permit reduced disclosure for interim periods. The unaudited condensed consolidated financial statements include all accounts of the Company and, in the opinion of management, include all recurring adjustments and normal accruals necessary for a fair statement of the Company’s financial position, results of operations and cash flows for the dates and periods presented. These unaudited condensed consolidated financial statements should be read in conjunction with the Company’s audited financial statements as of and for the year ended December 31, 2022 . Results for interim periods are not necessarily indicative of the results to be expected during the remainder of the current year or for any future period. All intercompany transactions, accounts and profits, have been eliminated in the unaudited condensed consolidated financial statements.

Summary of New Accounting Prono

Summary of New Accounting Pronouncements	3 Months Ended
	Mar. 31, 2023
Accounting Standards Update and Change in Accounting Principle [Abstract]
Summary of New Accounting Pronouncements	2. SUMMARY OF NEW ACCOUNTING PRONOUNCEMENTS Recently Adopted Accounting Pronouncements —In A ugust 2020, the Financial Accounting Standards Board ("FASB") issued Accounting Standard Update ("ASU") 2020-06, Debt—Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging—Contracts in Entity’s Own Equity (Subtopic 815-40)—Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity. The ASU simplifies accounting for convertible instruments by removing major separation models required under current U.S. GAAP. Consequently, more convertible debt instruments will be reported as a single liability instrument with no separate accounting for embedded conversion features. The ASU removes certain settlement conditions that are required for equity contracts to qualify for the derivative scope exception, which will permit more equity contracts to qualify for the exception. The ASU also simplifies the diluted net income per share calculation in certain areas. The new guidance was adopted as of January 1, 2022 and did not have a material impact on the Company’s unaudited condensed consolidated financial statements. In October 2021, the FASB issued ASU No. 2021-08, Business Combinations (Topic 805): Accounting for Contract Assets and Contract Liabilities from Contracts with Customers. Under the new guidance (ASC 805-20-30-28), the acquirer should determine what contract assets and/or contract liabilities it would have recorded under ASC 606 (the revenue guidance) as of the acquisition date, as if the acquirer had entered into the original contract at the same date and on the same terms as the acquiree. The new guidance was adopted as of January 1, 2023 and did not have a material impact on the Company’s unaudited condensed consolidated financial statements; however it may impact the accounting for future acquisitions. The future impact of this new guidance will be primarily a function of the facts and circumstances specific to any acquisitions consummated after adoption and therefore cannot be predicted.

Revenues and Accounts Receivabl

Revenues and Accounts Receivable	3 Months Ended
	Mar. 31, 2023
Revenues And Accounts Receivable [Abstract]
Revenues and Accounts Receivable	3. REVENUES AND ACCOUNTS RECEIVABLE The Company’s main revenue sources derive from the following revenue streams: Assessment, Permitting and Response Revenues —Assessment, Permitting and Response revenues are generated from multidisciplinary environmental consulting services. The majority of the contracts are fixed-price or time and material based. Measurement and Analysis Revenues —Measurement and Analysis revenues are generated from emissions sampling, testing and reporting services, leak detection services, ambient air monitoring services and laboratory testing services. The majority of the contracts are fixed-price or time-and-materials based. Remediation and Reuse Revenues —Remediation and Reuse revenues are generated from engineering, design, implementation and operating and maintenance (“O&M”) services primarily to treat contaminated water, remove contaminants from soil or create biogas from waste. Engineering, design and implementation contracts are predominantly fixed-fee and time-and-materials based. Services on the majority of O&M contracts are provided under long-term fixed-fee contracts. Disaggregation of Revenue —The Company disaggregates revenue by its operating segments . The Company believes disaggregating revenue into these categories achieves the disclosure objectives to depict how the nature, amount, and uncertainty of revenue and cash flows are affected by economic factors. Disaggregated revenue disclosures are provided in Note 18. Contract Balances —The Company presents contract balances for unbilled receivables (contract assets), as well as customer advances, deposits and deferred revenue (contract liabilities) within contract assets and accounts payable and other accrued expenses, respectively, on the unaudited condensed consolidated statements of financial position. Amounts are generally billed at periodic intervals (e.g. weekly, bi-weekly or monthly) as work progresses in accordance with agreed-upon contractual terms. The Company utilizes the practical expedient to not adjust the promised amount of consideration for the effects of a significant financing component as the period between when the Company transfers services to a customer and when the customer pays for those services is one year or less. Amounts recorded as unbilled receivables are generally for services the Company is not entitled to bill based on the passage of time. Under certain contracts, billing occurs subsequent to revenue recognition, resulting in contract assets. The Company sometimes receives advances or deposits from customers before revenue is recognized, resulting in contract liabilities. The following table presents the Company’s contract balances: March 31, December 31, 2023 2022 Contract assets $ 53,563 $ 52,403 Contract liabilities 10,932 18,549 Contract assets acquired through business acquisitions amounted to $ 0.2 million and $ 1.7 million as of March 31, 2023 and December 31, 2022 , respectively. No contract liabilities were acquired through business acquisitions as of March 31, 2023 and December 31, 2022. Revenue recognized during the three months ended March 31, 2023, included in the contract liabilities balance at the beginning of the year was $ 12.8 million. The revenue recognized from the contract liabilities consisted of the Company satisfying performance obligations during the normal course of business. The amount of revenue recognized from changes in the transaction price associated with performance obligations satisfied in prior periods during the three months ended March 31, 2023 was not material. Remaining Unsatisfied Performance Obligations —Remaining unsatisfied performance obligations represent the total dollar value of work to be performed on contracts awarded and in progress. The amount of remaining unsatisfied performance obligations increases with new contracts or additions to existing contracts and decreases as revenue is recognized on existing contracts. Contracts are included in the amount of remaining unsatisfied performance obligations when an enforceable agreement has been reached. As of March 31, 2023 and December 31, 2022, the estimated revenue expected to be recognized in the future related to performance obligations that are unsatisfied was approximately $ 98.2 million and $ 100.4 million, respectively. As of March 31, 2023, the Company expected to recognize approximately $ 79.1 million of this amount as revenue within a year and $ 19.1 million the year after . Accounts Receivable, Net —Th e Company extends non-interest-bearing trade credit to its customers in the ordinary course of business. Accounts receivable, net consisted of the following: March 31, December 31, Accounts receivable, invoiced $ 87,261 $ 95,055 Accounts receivable, other 503 1,571 Allowance for doubtful accounts ( 2,292 ) ( 1,915 ) Accounts receivable—net $ 85,472 $ 94,711 The Company did no t have any customers that exceeded 10.0 % of its gross receivables as of March 31, 2023 and December 31, 2022. During the three months ended March 31, 2023 the Company did no t have any customers that exceeded 10.0 % of its revenue. During the three months ended March 31, 2022, the Company had one customer who accounted for 17.3 % of revenue. The Company performs ongoing credit evaluations and based on past collection experience, the Company believes that the receivable balances from these largest customers do not represent a significant credit risk. The allowance for doubtful accounts consisted of the following: Beginning Bad Debt Charged to Other (1) Ending There months ended March 31, 2023 $ 1,915 $ 444 $ ( 67 ) $ — $ 2,292 Year ended December 31, 2022 4,581 ( 1,097 ) ( 1,696 ) 127 1,915 ____________________ (1) This amount consists of additions to the allowance due to business acquisitions.

Prepaid and Other Current Asset

Prepaid and Other Current Assets	3 Months Ended
	Mar. 31, 2023
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid and Other Current Assets	4. PREPAID AND OTHER CURRENT ASSETS Prepaid and other current assets consisted of the following: March 31, December 31, 2023 2022 Deposits $ 1,366 $ 1,394 Prepaid expenses 9,167 5,266 Supplies 4,074 3,632 Income tax receivable 571 694 Prepaid and other current assets $ 15,178 $ 10,986

Property and Equipment, Net

Property and Equipment, Net	3 Months Ended
	Mar. 31, 2023
Property, Plant and Equipment [Abstract]
Property and Equipment, Net	5. PROPERTY AND EQUIPMENT, NET Property and equipment are stated at cost or estimated fair value for assets acquired through business combinations. Depreciation and amortization are provided using the straight-line method over the estimated useful lives of the assets. Leasehold improvements are amortized using the straight-line method over the shorter of the remaining lease term, including options that are deemed to be reasonably assured, or the estimated useful life of the improvement. Property and equipment, net, consisted of the following: Estimated March 31, December 31, Useful Life 2023 2022 Lab and test equipment 7 years $ 22,992 $ 21,171 Vehicles 5 years 5,841 5,732 Equipment 3 - 7 years 42,819 40,940 Furniture and fixtures 7 years 2,853 2,841 Leasehold improvements 7 years 8,837 8,576 Aircraft 10 years — 931 Building 39 years 6,112 2,975 89,454 83,166 Land 725 725 Construction in progress 3,092 3,150 Less accumulated depreciation ( 52,586 ) ( 50,996 ) Total property and equipment— $ 40,685 $ 36,045 Total depreciation expense included in the unaudited condensed consolidated statements of operations was $ 2.2 million and $ 1.8 million for the three months ended March 31, 2023 and March 31, 2022, respective ly.

Leases

Leases	3 Months Ended
	Mar. 31, 2023
Leases [Abstract]
Leases	6. LEASES Leases are classified as either finance leases or operating leases based on criteria in ASC 842. The Company has finance leases for its vehicle and equipment leases and operating leases for its real estate space and office equipment leases. The Company’s operating and finance leases generally have original lease terms between 1 year and 15 years , an d in some instances include one or more options to renew. The Company includes options to extend the lease term if the options are reasonably certain of being exercised. The Company currently considers some of its renewal options to be reasonably certain to be exercised. Some leases also include early termination options, which can be exercised under specific conditions. The Company does not have material residual value guarantees or restrictive covenants associated with its leases. Finance and operating lease assets represent the right to use an underlying asset for the lease term, and finance and operating lease liabilities represent the obligation to make lease payments arising from the lease. The Company calculates the present value of its finance and operating leases using an estimated incremental borrowing rate (“IBR”), which requires judgment. For real estate operating leases, the Company estimates the IBR based on prevailing market rates for collateralized debt in a similar economic environment with similar payment terms and maturity dates commensurate with the terms of the lease. For all other leases, the Company estimates the IBR based on the stated interest rate on the contract. Since many of the inputs used to calculate the rate implicit in the leases are not readily determinable from the lessee’s perspective, the Company does not use the implicit interest rate. Certain leases contain variable payments, these payments are expensed as incurred and not included in the Company’s operating lease right-of-use assets and operating lease liabilities. These amounts primarily include payments for maintenance, utilities, taxes, and insurance and are excluded from the present value of the Company’s lease obligations. The Company does not record operating lease right-of-use assets or operating lease liabilities for leases with an initial term of 12 months or less. The Company also combines lease and non-lease components on all new or modified operating leases into a single lease component for all classes of assets. The components of lease expense were as follows: For the Three Months Ended March 31, Statement of Operations Location 2023 2022 Operating lease cost Lease cost Selling, general and administrative expense $ 2,741 $ 2,451 Variable lease cost Selling, general and administrative expense 326 367 Total operating lease cost 3,067 2,818 Finance lease cost Amortization of right of use assets Depreciation and amortization 1,154 939 Interest on lease liabilities Interest expense—net 130 112 Total finance lease cost 1,284 1,051 Total lease cost $ 4,351 $ 3,869 Supplemental cash flows information related to leases was as follows: For the Three Months Ended March 31, 2023 2022 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows used in operating leases $ 2,557 $ 2,302 Operating cash flows used in finance leases 130 112 Financing cash flows used in finance leases 1,029 944 Lease liabilities arising from new ROU assets: Operating leases 7,999 8,815 Finance leases 2,405 512 Weighted average remaining lease terms and weighted average discount rates were: March 31, 2023 Operating Leases Finance Leases Weighted average remaining lease term (years) 4.62 3.43 Weighted average discount rate 3.31 % 5.57 % March 31, 2022 Operating Leases Finance Leases Weighted average remaining lease term (years) 4.86 3.03 Weighted average discount rate 2.50 % 4.98 % The following is a schedule by year of the maturities of lease liabilities with original terms in excess of one year: Operating Leases Finance Leases Remainder of 2023 $ 7,117 $ 3,657 2024 8,554 3,543 2025 6,507 2,612 2026 5,006 1,902 2027 3,385 967 2028 and thereafter 4,787 135 Total undiscounted future minimum lease payments 35,356 12,816 Less imputed interest ( 2,693 ) ( 1,179 ) Total discounted future minimum lease payments $ 32,663 $ 11,637

Business Acquisitions

Business Acquisitions	3 Months Ended
	Mar. 31, 2023
Business Combinations [Abstract]
Business Acquisitions	7. BUSINESS ACQUISITIONS In line with the Company’s strategic growth initiatives, the Company acquired certain businesses during the three months ended March 31, 2023 and during the year ended December 31, 2022. The results of each of those acquired businesses are included in the unaudited condensed consolidated financial statements beginning on the acquisition date. Each transaction qualified as an acquisition of a business and was accounted for as a business combination. All acquisitions resulted in the recognition of goodwill. The Company paid these premiums resulting in such goodwill for a number of reasons, including expected synergies from combining operations of the acquiree and the Company while also growing the Company’s customer base, acquiring assembled workforces, expanding its presence in certain markets and expanding and advancing its product and service offerings. The Company recorded the assets acquired and liabilities assumed at their acquisition date fair value, with the difference between the fair value of the net assets acquired and the acquisition consideration reflected as goodwill. The identifiable intangible assets for significant acquisitions are valued using the excess earnings method discounted cash flow approach for customer relationships, the relief from royalty method for trade names, the patent and external proprietary software and developed technology, the “with and without” method for covenants not to compete and the replacement cost method for the internal proprietary software by incorporating Level 3 inputs as described under the fair value hierarchy of ASC 820. These unobservable inputs reflect the Company’s own assumptions about which assumptions market participants would use in pricing an asset on a non-recurring basis. These assets will be amortized over their respective estimated useful lives. Other purchase price obligations (primarily deferred purchase price liabilities and target working capital liabilities or receivables) are included on the unaudited condensed consolidated statements of financial position in accounts payable and other accrued liabilities, other non-current liabilities or accounts receivable-net in the case of working capital deficits. Contingent consideration outstanding from acquisitions are included on the unaudited condensed consolidated statements of financial position in business acquisition contingent consideration, current or in business acquisitions contingent consideration, long-term. The contingent consideration elements of the purchase price of the acquisitions are related to earn-outs which are based on the expected achievement of revenue or earnings thresholds as of the date of the acquisition and for which the maximum potential amount is limited. The Company considers several factors when determining whether or not contingent consideration liabilities are part of the purchase price, including the following: (i) the valuation of its acquisitions is not supported solely by the initial consideration paid, (ii) the former stockholders of acquired companies that remain as key employees receive compensation other than contingent consideration payments at a reasonable level compared with the compensation of the Company’s other key employees and (iii) contingent consideration payments are not affected by employment termination. The Company reviews and assesses the estimated fair value of contingent consideration at each reporting period. The Company may be required to make up to $ 9.5 million in aggregate earn-out payments between the years 2023 and 2026 in connection with certain of its business acquisitions, of which up to $ 2.6 million may be paid only in cash, up to $ 5.5 million may be paid only in common stock and up to $ 1.5 million may be paid, at the Company’s option, in cash or common stock. Transaction costs related to business combinations totaled $ 0.8 million and $ 0.5 million for the three months ended March 31, 2023 and March 31, 2022, respectively. These costs are expensed within selling, general and administrative expense in the accompanying unaudited condensed consolidated statements of operations. Acquisitions Completed During the Three Months Ended March 31, 2023 Frontier Analytical Laboratories (“Frontier”) —In January 2023, the Company completed the acquisition of Frontier by acquiring certain of its assets and operations. Frontier is a specialized environmental laboratory based in El Dorado Hills, CA. Environmental Alliance, Inc. (“EAI”) —In February 2023, the Company completed the acquisition of EAI by acquiring 100.0 % of its common stock. EAI provides environmental remediation and consulting services, and is based in Wilmington, DE. The following table summarizes the elements of the purchase price of the acquisitions completed during the three months ended March 31, 2023: Cash Common Other Contingent Total Frontier $ 1,146 $ — $ — $ — $ 1,146 EAI 5,390 — ( 342 ) 25 5,073 Total $ 6,536 $ — $ ( 342 ) $ 25 $ 6,219 The upfront cash payment made to acquire both of these acquisitions was funded through cash on hand. The other purchase price components of the EAI purchase price mainly consist of surplus working capital amounts. The preliminary purchase price attributable to the acquisitions was allocated as follows: Frontier EAI Total (1) Cash $ — $ 11 $ 11 Accounts receivable — 1,502 1,502 Other current assets — 121 121 Current assets — 1,634 1,634 Property and equipment 302 191 493 Customer relationships — 1,402 1,402 Trade names — 106 106 Covenants not to compete — 263 263 Goodwill 844 1,965 2,809 Total assets 1,146 5,561 6,707 Current liabilities — 488 488 Total liabilities — 488 488 Purchase price $ 1,146 $ 5,073 $ 6,219 ___________________________________ (1) The Company is continuing to obtain information to complete the valuation of certain of these acquisitions' assets and liabilities. Goodwill associated with the Frontier acquisition is deductible for income tax purposes. The weighted average useful lives for EAI identifiable customer relationships, tradenames and covenants not to compete are 7 years, 2 years and 5 years, respectively. Frontier is included in the Company’s Measurement and Analysis segment and EAI is included in the Remediation and Reuse segment. For the acquisitions completed during the three months ended March 31, 2023, the results of operations since the acquisition dates have been combined with those of the Company. The Company’s unaudited condensed consolidated statement of operations for the three months ended March 31, 2023 includes revenue of $ 1.0 million, and pre-tax income of $ 0.1 million, related to these acquisitions. Acquisitions Completed During the Year Ended December 31, 2022 Environmental Standards, Inc. (“Environmental Standards”) —In January 2022, the Company completed the acquisition of Environmental Standards, Inc. by acquiring 100.0 % of its common stock. Environmental Standards is a provider of environmental consulting and data validation services. Environmental Standards is based in Valley Forge, PA with satellite locations nationwide. Industrial Automation Group, Inc. (“IAG”) —In January 2022, the Company completed the acquisition of Industrial Automation Group, Inc. by acquiring certain of its employees and a covenant not to compete. IAG is based in Atlanta, GA. IAG provides highly specialized engineering services which are additive to the Company’s water treatment and renewable energy technology implementations. TriAD Environmental Consultants, Inc. (“TriAD”) —In August 2022, the Company completed the acquisition of TriAD Environmental Consultants, Inc. by acquiring 100.0 % of its common stock. TriAD is a provider of environmental consulting services. TriAD is based in Nashville, TN. AirKinetics, Inc. (“AirKinetics”) —In September 2022, the Company completed the acquisition of AirKinetics, Inc. by acquiring 100.0 % of its common stock. AirKinetics is a provider of emissions testing services. AirKinetics is based in Anaheim, CA. Huco Consulting, Inc. (“Huco”) —In November 2022, the Company completed the acquisition of Huco Consulting, Inc. by acquiring 100.0 % of its common stock. Huco primarily specializes in the implementation of environment, health and safety software for industrial, commercial and government clients. Huco is based in Houston, TX. Environmental Standards and Huco are included in the Company’s Assessment, Permitting and Response segment, IAG and TriAD are included in the Remediation and Reuse segment and AirKinetics is included in the Measurement and Analysis segment. For the acquisitions completed during the three months ended March 31, 2022, the results of operations since the acquisition dates have been combined with those of the Company. The Company’s unaudited condensed consolidated statement of operations for the three months ended March 31, 2022 includ es revenue of $ 3.3 million and pre-tax income of $ 0.8 million. During the three months ended March 31, 2023, measurement period adjustments of $ 0.2 million were recorded to goodwill as a result of the Company’s efforts to complete the valuation of certain acquired assets and assumed liabilities (Note 8). Supplemental Unaudited Pro-Forma — The unaudited condensed consolidated financial information summarized in the following table gives effect to the 2023 and the 2022 acquisitions discussed above assuming they occurred on January 1, 2022. These unaudited consolidated pro forma operating results do not assume any impact from revenue, cost or other operating synergies that are expected or may have been realized as a result of the acquisitions. These unaudited consolidated pro forma operating results are presented for illustrative purposes only and are not indicative of the operating results that would have been achieved had the acquisitions occurred on January 1, 2022, nor does the information purport to reflect results for any future period. For the Three Months Ended March 31, 2023 2022 As Acquisitions Consolidated As Acquisitions Consolidated Revenues $ 131,428 $ 433 $ 131,861 $ 134,680 $ 5,625 $ 140,305 Net (loss) income ( 14,719 ) ( 67 ) ( 14,786 ) ( 7,536 ) 722 ( 6,814 )

Goodwill and Intangible Assets

Goodwill and Intangible Assets	3 Months Ended
	Mar. 31, 2023
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets	8. GOODWILL AND INTANGIBLE ASSETS Amounts related to goodwill are as follows: Assessment, Measurement Remediation Total Balance as of December 31, 2022 $ 185,116 $ 86,205 $ 52,547 $ 323,868 Goodwill acquired during the period — 844 1,965 2,809 Acquisitions measurement period adjustments ( 169 ) ( 10 ) — ( 179 ) Balance as of March 31, 2023 $ 184,947 $ 87,039 $ 54,512 $ 326,498 Amounts related to finite-lived intangible assets are as follows: March 31, 2023 Estimated Gross Accumulated Total Finite lived intangible assets Customer relationships 2 - 15 years $ 209,426 $ 100,404 $ 109,022 Covenants not to compete 4 - 5 years 33,805 29,020 4,785 Trade names 1 - 5 years 22,167 18,708 3,459 Proprietary software 3 - 5 years 23,324 16,942 6,382 Patent 16 years 17,479 3,856 13,623 Total other intangible assets $ 306,201 $ 168,930 $ 137,271 December 31, 2022 Estimated Gross Accumulated Total Finite lived intangible assets Customer relationships 2 - 15 years $ 208,024 $ 95,768 $ 112,256 Covenants not to compete 4 - 5 years 33,542 28,280 5,262 Trade names 1 - 5 years 22,061 18,256 3,805 Proprietary software 3 - 5 years 22,698 15,810 6,888 Patent 16 years 17,479 3,583 13,896 Total other intangible assets $ 303,804 $ 161,697 $ 142,107 Intangible assets with finite lives are stated at cost, less accumulated amortization and impairment losses, if any. These intangible assets are amortized using the straight-line method over the estimated useful lives of the assets. Amortization expense was $ 7.2 million and $ 9.4 million for the three months ended March 31, 2023 and March 31, 2022, respectively. Future amortization expense is estimated to be as follows for each of the five following years and thereafter: December 31, 2023 (remaining) 20,920 2024 24,607 2025 17,727 2026 13,952 2027 13,429 Thereafter 46,636 Total $ 137,271

Accounts Payable and Other Accr

Accounts Payable and Other Accrued Liabilities	3 Months Ended
	Mar. 31, 2023
Payables and Accruals [Abstract]
Accounts Payable and Other Accrued Liabilities	9. ACCOUNTS PAYABLE AND OTHER ACCRUED LIABILITIES Accounts payable and other accrued liabilities consisted of the following: March 31, December 31, 2023 2022 Accounts payable $ 24,399 $ 25,353 Accrued expenses 16,311 14,754 Other business acquisitions purchase 450 1,185 Contract liabilities 10,932 18,549 Other current liabilities 3,328 3,571 Total accounts payable and $ 55,420 $ 63,412

Accrued Payroll and Benefits

Accrued Payroll and Benefits	3 Months Ended
	Mar. 31, 2023
Statement of Financial Position [Abstract]
Accrued Payroll and Benefits	10. ACCRUED PAYROLL AND BENEFITS Accrued payroll and benefits consisted of the following: March 31, December 31, 2023 2022 Accrued bonuses $ 3,559 $ 8,624 Accrued paid time off 1,161 1,088 Accrued payroll 9,084 8,410 Accrued other 2,548 2,406 Total accrued payroll and benefits $ 16,352 $ 20,528

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2023
Income Tax Disclosure [Abstract]
Income Taxes	11. INCOME TAXES The Company calculates its interim income tax provision in accordance with ASC Topic 270, Interim Reporting (“ASC 270”), and ASC 740. The Company’s effective tax rate (“ETR”) from continuing operations was ( 10.2 )% and ( 20.2 )% for the three months ended March 31, 2023 and March 31, 2022, respectively. Income tax expense recorded by the Company during the three months ended March 31, 2023 and March 31, 2022 was $ 1.4 million and $ 1.3 million, respectively. The difference between the ETR and federal statutory rate of 21.0 % is primarily attributable to items recorded for U.S. GAAP but permanently disallowed for U.S. federal income tax purposes, recognition of a U.S. federal and state valuation allowance and state and foreign income tax provisions. A valuation allowance is recorded when it is more-likely-than-not some of the Company’s deferred tax assets may not be realized. Significant judgment is applied when assessing the need for a valuation allowance and the Company considers future taxable income, reversals of existing deferred tax assets and liabilities and ongoing prudent and feasible tax planning strategies, in making such assessment. As of March 31, 2023, the Company’s U.S. federal, state and various foreign net deferred tax assets are not more-likely-than-not to be realized and a full valuation allowance is maintained. The Company records uncertain tax positions in accordance with ASC 740, on the basis of a two-step process in which (i) the Company determines whether it is more likely than not a tax position will be sustained on the basis of the technical merits of such position and (ii) for those tax positions meeting the more-likely-than-not recognition threshold, the Company would recognize the largest amount of tax benefit that is more than 50.0% likely to be realized upon ultimate settlement with the related tax authority. The Company has determined it has no uncertain tax positions as of March 31, 2023 . The Company classifies interest and penalties recognized on uncertain tax positions as a component of income tax expense.

Debt

Debt	3 Months Ended
	Mar. 31, 2023
Debt Disclosure [Abstract]
Debt	12. DEBT Debt consisted of the following: March 31, December 31, 2023 2022 Term loan facility $ 164,062 $ 166,250 Revolving line of credit — — Less deferred debt issuance costs ( 1,595 ) ( 1,725 ) Total debt 162,467 164,525 Less current portion of long-term debt ( 13,125 ) ( 12,031 ) Long-term debt, less current portion $ 149,342 $ 152,494 Deferred Financing Costs —Costs relating to debt issuance have been deferred and are presented as discounted against the underlying debt instrument. These costs are amortized to interest expense over the terms of the underlying debt instruments. 2021 Credit Facility —On April 27, 2021 , the Company entered into a Senior Secured Credit Agreement providing for a $ 300.0 million credit facility comprised of a $ 175.0 million term loan and a $ 125.0 million revolving line of credit (the “2021 Credit Facility”), and used a portion of the proceeds from the 2021 Credit Facility to repay all amounts outstanding under the prior credit facility. The revolving line of credit portion of the 2021 Credit Facility includes a $ 20.0 million sublimit for the issuance of letters of credit. Subject to certain exceptions, all amounts under the 2021 Credit Facility will become due on April 27, 2026 . The Company has the option to borrow incremental term loans or request an increase in the aggregate commitments under the revolving credit facility up to an aggregate amount of $ 150.0 million subject to the satisfaction of certain conditions. The 2021 Credit Facility term loan must be repaid in quarterly installments and shall amortize at the following future quarterly rates: Date Quarterly Installment Rate June 30, 2023 1.25 % September 30, 2023 1.25 % December 31, 2023 1.88 % March 31, 2024 1.88 % June 30, 2024 1.88 % September 30, 2024 1.88 % December 31, 2024 1.88 % March 31, 2025 1.88 % June 30, 2025 1.88 % September 30, 2025 1.88 % December 31, 2025 2.50 % March 31, 2026 2.50 % April 27, 2026 Remaining balance Repayments of quarterly installments were scheduled to begin with the quarter ended December 31, 2021. The first quarterly installment repayment, amounting to $ 2.2 million, was paid in January 2022. Exclusive of the payment made in respect of the quarter ended December 31, 2021, the quarterly installment repayments for the three months ended March 31, 2022 amounted to $ 2.2 million. The December 31, 2022 installment repayment, amounting to $ 2.2 million, was paid in January 2023. The March 31, 2023 installment repayment, amounting to $ 2.2 million, was paid in April 2023. The 2021 Credit Facility term loan and the revolver bear interest subject to the Company’s leverage ratio and LIBOR as follows: Pricing Tier Consolidated Senior Credit Facilities Senior Credit Facilities Commitment Letter of Credit Fee 1 ≥ 3.75 x to 1.0 2.50 % 1.50 % 0.25 % 2.50 % 2 < 3.75 x to 1.0 but ≥ 3.25 to 1.0 2.25 1.25 0.23 2.25 3 < 3.25 x to 1.0 but ≥ 2.50 to 1.0 2.00 1.00 0.20 2.00 4 < 2.50 x to 1.0 but ≥ 1.75 to 1.0 1.75 0.75 0.15 1.75 5 < 1.75 x to 1.0 1.50 0.50 0.15 1.50 The Company is currently in discussions regarding the transition of LIBOR to an adjusted benchmark rate to be effective on or before June 30, 2023. The transition to an adjusted interest rate is not expected to materially impact the interest rate paid by the Company. On January 27, 2022, the Company entered into an interest rate swap transaction fixing the floating component of the interest rate on $ 100.0 million of borrowings to 1.39 % until January 27, 2025 . Additionally, effective September 1, 2022, the Company received an interest rate reduction of 0.05 % under the 2021 Credit Facility based on the Company’s achievement of certain sustainability and environmental, social and governance related objectives as provided for in the 2021 Credit Facility. The 2021 Credit Facility includes a number of covenants imposing certain restrictions on the Company’s business, including, among other things, restrictions on the Company’s ability, subject to certain exceptions and baskets, to incur indebtedness, incur liens on its assets, agree to any additional negative pledges, pay dividends or repurchase stock, limit the ability of its subsidiaries to pay dividends or distribute assets, make investments, enter into any transaction of merger or consolidation, liquidate, wind-up or dissolve, or convey any part of its business, assets or property, or acquire the business, property or assets of another person, enter into sale and leaseback transactions, enter into certain transactions with affiliates, engage in any material line of business substantially different from those engaged on the closing date, modify the terms of indebtedness subordinated to the loans incurred under the 2021 Credit Facility and modify the terms of its organizational documents. The 2021 Credit Facility also includes financial covenants which required the Company to remain below a maximum total net leverage ratio of 4.25 times until the fiscal quarter ended September 31, 2022, which stepped down to 4.00 times during the fiscal quarter ending December 31, 2022 and applies through and including the fiscal quarter ending September 30, 2023 and then further steps down to 3.75 times beginning with the fiscal quarter ending December 31, 2023, and a minimum fixed charge coverage ratio of 1.25 times. As of March 31, 2023 and December 31, 2022, the Company’s consolidated total leverage ratio (as defined in the 2021 Credit Facility) was 1.4 times an d 1.3 times, respe ctively, and the Company was in compliance with all covenants under the 2021 Credit Facility. The 2021 Credit Facility requires customary mandatory prepayments of the term loan and revolver and cash collateralization of letters of credit, subject to customary exceptions, including 100.0 % of the proceeds of debt not permitted by the 2021 Credit Facility, 100.0 % of the proceeds of certain dispositions, subject to customary reinvestment rights, where applicable, and 100.0 % of insurance or condemnation proceeds, subject to customary reinvestment rights, where applicable. The 2021 Credit Facility also includes customary events of default and related acceleration and termination rights. The weighted average interest rate on the 2021 Credit Facility for the three months ended March 31, 2023 and March 31, 2022 was 6.1 % and 1.8 %, respectively. The Company’s obligations under the 2021 Credit Facility are guaranteed by certain of the Company’s existing and future direct and indirect subsidiaries, and such obligations are secured by substantially all of the Company’s assets, including the capital stock or other equity interests in those subsidiaries. Equipment Line of Credit —The Company had a $ 10.0 million equipment leasing facility for the purchase of equipment and related freight, installation costs and taxes paid. Any unused capacity on this equipment leasing facility expired on March 31, 2023 . Interest on the line of credit was determined based on a three-year swap rate at the time of funding. Equipment leased through this line of credit met the finance lease criteria as per ASC 842 and accordingly is accounted for as finance lease right-of-use assets and finance lease liabilities (Note 6). The following is a schedule of the aggregate annual maturities of long-term debt presented on the unaudited condensed consolidated statement of financial position, based on the terms of the 2021 Credit Facility: March 31, 2024 $ 13,125 2025 13,125 2026 15,312 2027 122,500 2028 — Total $ 164,062

Fair Value of Financial Instrum

Fair Value of Financial Instruments	3 Months Ended
	Mar. 31, 2023
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	13. FAIR VALUE OF FINANCIAL INSTRUMENTS The following financial instruments are measured at fair value on a recurring basis using significant unobservable inputs (Level 3): March 31, December 31, 2023 2022 Interest rate swap (1) $ 5,078 $ 6,046 Total assets $ 5,078 $ 6,046 Business acquisitions contingent consideration, $ 4,734 $ 3,801 Business acquisitions contingent consideration, 3,121 4,454 Conversion option 26,636 25,731 Total liabilities $ 34,491 $ 33,986 _____________________________ (1) Included in other assets in the unaudited condensed consolidated statement of financial position. The estimated fair value amounts shown above are not necessarily indicative of the amounts that the Company would realize upon disposition, nor do they indicate the Company’s intent or ability to dispose of the financial instrument. The following table sets forth the Company’s financial instruments that were measured at fair value on a recurring basis: Interest Total Business Business Conversion Total Balance—at January 1, 2022 $ — $ — $ 31,450 $ 4,350 $ 23,081 $ 58,881 Acquisitions — — — 1,216 — 1,216 Changes in fair value included in earnings 3,005 3,005 ( 21 ) — 556 535 Payment of contingent consideration — — ( 30,000 ) — — ( 30,000 ) Balance—at March 31, 2022 $ 3,005 $ 3,005 $ 1,429 $ 5,566 $ 23,637 $ 30,632 Balance—at January 1, 2023 $ 6,046 $ 6,046 $ 3,801 $ 4,454 $ 25,731 $ 33,986 Acquisitions — — 25 — — 25 Changes in fair value included in earnings ( 968 ) ( 968 ) ( 515 ) 117 905 507 Payment of contingent consideration — — ( 27 ) — — ( 27 ) Reclass of long term to short term — — 1,450 ( 1,450 ) — — Balance—at March 31, 2023 $ 5,078 $ 5,078 $ 4,734 $ 3,121 $ 26,636 $ 34,491 Quantitative Information about Assets and Liabilities Measured at Fair Value on a Recurring Basis Using Significant Unobservable Inputs (Level 3): Interest Rate Swap —The interest rate swap fair value is estimated based on a mid-market price for the swap as of the close of business of the reporting period. The fair value is prepared by discounting future cash flows of the swap to arrive at a current value of the swap. Forward curves and volatility levels inputs are determined on the basis of observable market inputs when available and on the basis of estimates when observable market inputs are not available. The Company does not apply hedge accounting but instead recognizes the instrument at fair value on the unaudited condensed consolidated statement of financial position within other assets, with changes in fair value recognized as other income (expense) in each reporting period. Business Acquisitions Contingent Consideration —The fair value of the contingent consideration payable associated with the acquisitions of CTEH and Sensible was determined using a Monte Carlo simulation of earnings in a risk-neutral Geometric Brownian Motion framework. The fair value of the contingent consideration payable associated with the acquisition of Environmental Standards was determined using a Probabilistic (Scenario Based) method. The fair values of the contingent consideration payables for the other acquisitions were calculated based on expected target achievement amounts, which are measured quarterly and then subsequently adjusted to actuals at the target measurement date. The method used to price these liabilities is considered level 3 due to the subjective nature of the unobservable inputs used to determine the fair value. The input is the expected achievement of earn-out thresholds. Conversion Option —The fair value of the conversion option associated with the issuance of the Convertible and Redeemable Series A-2 Preferred Stock (Note 15) w as estimated using a “with-and-without” method. The “with-and-without” methodology considers the value of the security on an as-is basis and then without the embedded conversion premium. The difference between the two scenarios is the implied fair value of the embedded derivative. The unobservable input is the required rate of return on the Series A-2. The considerable quantifiable inputs in the valuation relate to the timing of conversions or redemptions.

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2023
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	14. COMMITMENTS AND CONTINGENCIES Leases —The Company leases office facilities over various terms expiring through 2031. Certain of these operating leases contain rent escalation clauses. The Company also has office equipment leases that expire through 2028 (Note 6 and 12). Other Commitments —The Company has commitments under the 2021 Credit Facility, its equipment line of credit and its lease obligations (Note 6 and 12). Contingencies —The Company is subject to purchase price contingencies related to earn-outs associated with certain acquisitions (Note 7 and 13). Legal —In the normal course of business, the Company is at times subject to pending and threatened legal actions. In management’s opinion, the potential loss resulting from the resolution of these matters is not expected to have a material effect on the unaudited condensed consolidated results of operations, financial position or cash flows of the Company.

Convertible and Redeemable Seri

Convertible and Redeemable Series A-2 Preferred Stock	3 Months Ended
	Mar. 31, 2023
Temporary Equity Disclosure [Abstract]
Convertible and Redeemable Series A-2 Preferred Stock	15. CONVERTIBLE AND REDEEMABLE SERIES A-2 PREFERRED STOCK On April 13, 2020, the Company entered into an agreement to issue 17,500 shares of the Convertible and Redeemable Series A-2 Preferred Stock with a par value of $ 0.0001 per share an d a detachable warrant to purchase shares of the Company’s common stock with a 10-year life, in exchange for gross proceeds of $ 175.0 million, net of $ 1.3 million debt issuance costs. The Convertible and Redeemable Series A-2 Preferred Stock warrants were exercised in full on July 30, 2020. The Company paid dividends on shares of the Convertible and Redeemable Series A-2 Preferred Stock of $ 4.1 million during both the three months ended March 31, 2023 and March 31, 2022. The Convertible and Redeemable Series A-2 Preferred Stock terms include the following: (i) no mandatory redemption, (ii) no stated value cash repayment obligation other than in the event of certain defined liquidation events, (iii) only redeemable at the Company’s option, (iv) convertible into common stock beginning on the four year anniversary of issuance at a 15.0 % discount to the common stock market price (with a limit of $ 60.0 million in stated value of Convertible and Redeemable Series A-2 Preferred Stock eligible to be converted in any 60-day period prior to the seventh anniversary of issuance and the amount of stated value of the Convertible and Redeemable Series A-2 Preferred Stock eligible for conversion limited to $ 60.0 million during year 5 and $ 120.0 million (which includes the aggregate amount of the stated value of the Convertible and Redeemable Series A-2 Preferred Stock and any accrued but unpaid dividends added to such stated value of any shares of Convertible and Redeemable Series A-2 Preferred Stock converted in year 5) during year 6), (v) 9.0 % dividend rate per year with required quarterly cash payments, (vi) in an event of noncompliance, the dividend rate shall increase to 12.0 % per annum for the first 90-day period from and including the date the noncompliance event occurred, and thereafter shall increase to 14.0 % per annum, (vii) debt incurrence test ratio of 4.5 times, and (viii) minimum repayment amount of $ 25.0 million. The Company may, at its option on any one or more dates, redeem all or a minimum portion (the lesser of (i) $ 25.0 million in aggregate stated value of the Convertible and Redeemable Series A-2 Preferred Stock and (ii) all of the Convertible and Redeemable Series A-2 Preferred Stock then outstanding) of the outstanding Convertible and Redeemable Series A-2 Preferred Stock in cash. With respect to any redemption of any share of the Convertible and Redeemable Series A-2 Preferred Stock prior to the third-year anniversary, the Company is subject to a make whole penalty in which the holders of the Convertible and Redeemable Series A-2 Preferred Stock are guaranteed a minimum repayment equal to outstanding redeemed stated value plus three years of dividends accrued or accruable thereon. The Convertible and Redeemable Series A-2 Preferred Stock does not meet the definition of a liability pursuant to “ASC 480- Distinguishing Liabilities from Equity.” However, as (i) the instrument is redeemable upon a change of control as defined in the certificate of designations governing the terms of the Convertible and Redeemable Series A-2 Preferred Stock, and (ii) the Company cannot assert it would have sufficient authorized and unissued shares of common stock to settle all future conversion requests due to the variable conversion terms, the instrument is redeemable upon the occurrence of events that are not solely within the control of the Company, and therefore the Company classifies the Convertible and Redeemable Series A-2 Preferred Stock as mezzanine equity. Subsequent adjustment of the carrying value of the instrument is required if the instrument is probable of becoming redeemable. As of March 31, 2023, the Company has determined that a change of control is not probable. Additionally, as of March 31, 2023, the Company has determined that it is not probable that there will be a future conversion request that the Company is unable to settle with authorized and issued shares based on the Company’s current stock price and available shares as well as the Company’s monitoring efforts to ensure there are a sufficient number of shares available to settle any conversion request. Therefore, as of March 31, 2023, the Company has determined that the instrument is not probable of becoming redeemable, and does not believe subsequent adjustment of the carrying value of the instrument will be necessary. The Convertible and Re deemable Series A-2 Preferred Stock contains a conversion option of the preferred shares to shares of common stock beginning on the fourth-year anniversary of the issuance date. As of March 31, 2023 and December 31, 2022, this conversion embedded feature had a net fair value of $ 26.6 million and $ 25.7 million, respectively. The change in net fair value of $ 0.9 million and $ 0.6 million for the three months ended March 31, 2023 and March 31, 2022, respectively, was recorded to other expense.

Stockholder's Equity

Stockholder's Equity	3 Months Ended
	Mar. 31, 2023
Equity [Abstract]
Stockholders' Equity	16. STOCKHOLDERS’ EQUITY Authorized Capital Stock— The Company was authorized to issue 190,000,000 shares of common stock, with a par value of $ 0.000004 per share as of March 31, 2023 and December 31, 2022. Common Stock Issuances — The Co mpany issued the following shares of common stock: Three Months Ended March 31, 2023 2022 Shares Average Price per Share Total Shares Average Price per Share Total Exercise of options 124,455 $ 21.61 $ 2,690 30,607 $ 14.03 $ 429 Restricted shares, net (1) 90,116 36.81 — 25,289 66.58 — Total 214,571 $ 27.99 $ 2,690 55,896 $ 37.81 $ 429 (1) Represents the non-cash release of common shares due to the vesting of restricted stock. Employee Equity Incentive Plans —The Company has two plans under which stock-based awards have been issued: (i) the Montrose Amended & Restated 2017 Stock Incentive Plan (“2017 Plan”) and (ii) the Montrose Amended & Restated 2013 Stock Option Plan (“2013 Plan”) (collectively the “Plans”). As of March 31, 2023, and March 31, 2022, there was $ 146.6 million and $ 173.1 million, respectively, of total unrecognized stock compensation expense related to unvested options, restricted stock and stock appreciation rights granted under the Plans. Such unrecognized expense is expected to be recognized over a weighted-average four year period. The following number of shares were authorized to be issued and available for grant: March 31, 2023 2017 Plan 2013 Plan Total Shares authorized to be issued 6,329,913 2,037,019 8,366,932 Shares available for grant (1) 893,522 — 893,522 March 31, 2022 2017 Plan 2013 Plan Total Shares authorized to be issued 8,272,487 1,904,644 10,177,131 Shares available for grant (1) 577,139 — 577,139 (1) In January 2023 and January 2022 the Board of Directors ratified the addition of 1,189,801 and 1,185,112 shares of common stock, respectively, to the number of shares available for issuance under the 2017 Plan pursuant to the annual increase provision of such plan. Unless the Board of Directors determines otherwise, additional annual increases will be effective on each January 1, through January 1, 2027. The 2017 Plan permits the company to settle awards, if and when vested, in cash at its discretion. Pursuant to the terms of the 2017 Plan, the number of shares authorized for issuance thereunder will only be reduced with respect to shares of common stock actually issued upon exercise or settlement of an award. Shares of common stock subject to awards that have been canceled, expired, forfeited or otherwise not issued under an award and shares of common stock subject to awards settled in cash do not count as shares of common stock issued under the 2017 Plan. Shares available for grant exclude awards of stock appreciation rights approved in December 2021 that are subject to vesting based on the achievement of certain market conditions, which have not yet been, and may not be, a chieved. See footnote 1 to the table in Common Stock Reserved for Future Issuance below for additional information on stock appreciation rights. Total stock compensation expense for the Plans was as follows: Three Months Ended March 31, 2023 2022 2017 plan 2013 2017 plan 2013 Options Restricted SARs Options Total Options Restricted SARs Options Total Cost of revenue $ 349 $ 543 $ — $ — $ 892 $ 294 $ — $ — $ — $ 294 Selling, general and 1,724 8,154 2,265 — 12,143 1,979 5,792 2,360 — 10,131 Total $ 2,073 $ 8,697 $ 2,265 $ — $ 13,035 $ 2,273 $ 5,792 $ 2,360 $ — $ 10,425 Montrose Amended & Restated 2017 Stock Incentive Plan Restricted Stock Awards and Restricted Stock Units— The Company issues restricted stock awards ("RSAs") to certain 2017 Plan participants as Director’s compensation. There were 17,346 and 10,920 RSAs granted during the three months ended March 31, 2023 and March 31, 2022, respectively. These RSAs vest one year from the date of grant, or, in each case, in full upon a change in control, subject to the participant’s continued service as a Director throughout such date, or upon retirement. Members of the Board of Directors that receive stock-based compensation are treated as employees for accounting purposes. In the first quarter of 2023, the Board of Directors approved the grant of 200,423 restricted stock units (“RSUs”) to certain senior non-executive employees of the Company, in lieu of options. These RSUs represent the right to receive one share of the Company’s common stock upon vesting. These RSUs vest annually over a 4-year period from the date of grant, subject to continued service through each such date. In the first quarter of 2023 and 2022, the Board of Directors approved the grant of RSUs under certain supplemental incentive plans ("SI Plans"). There were 246,417 and 95,404 RSUs issued under these SI Plans during the three months ended March 31, 2023 and March 31, 2022, respectively. The majority of the RSUs issued in the first quarter of 2023 vested 1/3 on the date of grant, and will vest 1/3 on the one-year anniversary of the grant, and 1/3 on the two-year anniversary of the grant, subject to continued service through each such date. The remaining RSUs vest a nnually over a 4-year period fro m the date of grant, subject to continued service through each such date. RSAs and RSUs activity was as follows: Three Months Ended March 31, 2023 2022 Shares Average Price per Share Fair Value Shares Average Price per Share Fair Value Awards granted 464,186 $ 32.62 $ 15,140 106,324 $ 46.82 $ 4,978 There were an aggregate of 90,116 and 25,289 shares underlying RSAs and RSUs that became fully vested and were released as unrestricted shares of common stock during the three months ended March 31, 2023 and March 31, 2022 , respectively. There were no forfeitures of RSAs or RSUs during the three months ended March 31, 2023 and March 31, 2022. There were an aggregate of 2,528,383 and 2,064,197 shares underlying outstanding RSAs and RSUs awards as of March 31, 2023 and March 31, 2022, respectively. Stock Appreciation Rights— As of M arch 31, 2023, there were 3,000,000 units of stock appreciation rights (“SARs”) outstanding under the 2017 Plan. These SARs represent the right to receive, upon exercise, a payment equal to the excess of (a) the fair market value of one share of the Company’s common stock, over (b) an exercise price of $ 66.79 , payable, at the Company’s election, in cash or shares of common stock. These SARs vest on the 5th anniversary of the date of grant based on achievement of performance hurdles over a five year period, subject to continued service on the vesting date. The performance hurdles are as follows: SARs Stock Price Performance Hurdle Portion of SARs Subject to Performance Hurdle $ 133.58 1/3 $ 166.98 1/3 $ 200.37 1/3 The performance hurdles shall be deemed achieved if the average trading price per share of the Company’s common stock equals or exceeds the applicable stock price performance hurdle set forth above for the trading days falling in a consecutive 20-day period prior to the vesting date. None of the market conditions have been achieved as of March 31, 2023. The SARs expire 10 years after the grant date. The fair value of these SARs at the grant date was $ 46.0 million. The weighted average remaining contract life of these SARs as of March 31, 2023 was 8.71 years. Options —Options issued to all optionees under the 2017 P lan vest over 4-years from the date of issuance (or earlier vesting start date, as determined by the Board of Directors) as follows: one half on the second anniversary of date of grant and the remaining half on the fourth anniversary of the date of grant, with the exception of certain annual grants to certain executive officers, which vest annually over a 3-year and 1-year period. The following summarizes the options activity of the 2017 Plan: Options to Weighted- Weighted Weighted Aggregate Outstanding as of January 1, 2022 2,036,729 $ 26 $ 14 8.30 $ 91,030 Granted 547,884 44 16 — — Forfeited/ cancelled ( 23,082 ) 36 — — — Exercised ( 11,547 ) 27 — — 313 Outstanding as of March 31, 2022 2,549,984 30 14 8.46 59,955 Outstanding as of January 1, 2023 2,579,566 $ 31 $ 15 7.76 $ 37,292 Granted 233,955 32 14 — — Forfeited/ cancelled ( 34,619 ) 35 — — — Exercised ( 101,279 ) 25 — — 2,467 Outstanding as of March 31, 2023 2,677,623 $ 31 $ 15 7.78 $ 21,127 Exercisable at March 31, 2023 1,305,511 29 — 7.19 11,880 The following weighted-average assumptions were used in the Black-Sholes option-pricing model calculation: March 31, March 31, 2023 2022 Common stock value (per share) $ 32.16 $ 44.11 Expected volatility 33.79 % 33.45 % Risk-free interest rate 3.72 % 1.74 % Expected life (years) 7.00 6.33 Forfeiture rate None None Dividend rate None None Montrose Amended & Restated 2013 Stock Option Plan — The following summarizes the activity of the 2013 Plan: Options to Weighted- Weighted Weighted Aggregate Outstanding as of January 1, 2022 897,674 $ 6 $ 2 4.37 $ 57,529 Exercised ( 19,060 ) 6 — — 821 Outstanding as of March 31, 2022 878,614 6 2 4.13 40,860 Outstanding as of January 1, 2023 855,695 $ 6 $ 2 3.31 $ 32,478 Exercised ( 23,176 ) 9 — — 963 Outstanding as of March 31, 2023 832,519 $ 6 $ 2 3.03 $ 24,393 Exercisable at March 31, 2023 832,519 6 — 3.03 24,393 Total shares outstanding from exercised options were 1,434,885 shares and 1,239,697 share s as of March 31, 2023 and March 31, 2022, respectively. Common Stock Reserved for Future Issuances — The Company has reserved certain stock of its authorized but unissued common stock for possible future issuance in connection with the following: March 31, 2023 2022 Montrose 2013 Stock Incentive Plan 832,519 878,614 Montrose 2017 Stock Incentive Plan (1) 8,722,930 7,893,918 Total 9,555,449 8,772,532 (1) In January 2023 and 2022, the Board of Directors ratified the addition of 1,189,801 and 1,185,112 sha res of common stock, respectively, to the number of shares available for issuance under the 2017 Plan pursuant to the annual increase provision of such plan. Unless the Board of Directors determines otherwise, additional annual increases will be effective on each January 1, through January 1, 2027. The 2017 Plan permits the company to settle awards, if and when vested, in cash at its discretion. Pursuant to the terms of the 2017 Plan, the number of shares authorized for issuance thereunder will only be reduced with respect to shares of common stock actually issued upon exercise or settlement of an award. Shares of common stock subject to awards that have been canceled, expired, forfeited or otherwise not issued under an award and shares of common stock subject to awards settled in cash do not count as shares of common stock issued under the 2017 Plan. The Company expects to have sufficient shares available under the 2017 Plan to satisfy the future settlement of outstanding awards. Shares reserved for future issuance include 3,000,000 shares underlying the 3,000,000 performance SARs granted in December 2021 that are subject to vesting based on the achievement of certain market conditions. Assuming achievement at the highest price performance hurdle, approximately 2,000,000 shares of common stock would be issued upon vesting of these performance SARs. To date, none of the market conditions have been achieved.

Net Loss Per Share

Net Loss Per Share	3 Months Ended
	Mar. 31, 2023
Earnings Per Share [Abstract]
Net Loss Per Share	17. NET LOSS PER SHARE Basic net loss per share is computed by dividing net loss attributable to common stockholders by the weighted average number of common shares outstanding during each period. The Convertible and Redeemable Series A-2 Preferred Stock is considered a participating security during the applicable period. Net losses are not allocated to the Convertible and Redeemable Series A-2 stockholders, as they were not contractually obligated to share in the Company’s losses. Diluted net loss per share is computed by dividing net loss attributable to common stockholders by the weighted average number of common and dilutive common equivalent shares outstanding for the period using the treasury-stock method or the as-converted method. Potentially dilutive shares are comprised of RSAs, RSUs, SARs and shares of common stock underlying stock options outstanding under the Plans. During the three months ended March 31, 2023 and March 31, 2022, there is no difference in the number of shares used to calculate basic and diluted shares outstanding during the applicable period due to the Company’s net loss attributable to common stockholders and potentially dilutive shares being anti-dilutive. The following table summarizes the computation of basic and diluted net loss per share attributable to common stockholders of the Company: Three Months Ended March 31, (In thousands, except for net loss per share) 2023 2022 Net loss $ ( 14,719 ) $ ( 7,536 ) Convertible and redeemable series A-2 preferred ( 4,100 ) ( 4,100 ) Net loss attributable to common stockholders ( 18,819 ) ( 11,636 ) Weighted-average common shares outstanding – 29,857 29,662 Net loss per share attributable to common $ ( 0.63 ) $ ( 0.39 ) The following common stock equivalents were excluded from the calculation of diluted net loss per share attributable to common stockholders because their effect would have been anti-dilutive: March 31, 2023 (1) 2022 (1) Stock options 3,510,142 2,034,041 Restricted stock 2,151,785 1,777,958 Series A-2 4,735,220 4,329,640 SARs 3,000,000 3,000,000 _____________________________ (1) Includes 7,362,459 and 5,008,269 common stock equivalents that are out of the money as of March 31, 2023 and March 31, 2022 , respectively.

Segment Information

Segment Information	3 Months Ended
	Mar. 31, 2023
Segment Reporting [Abstract]
Segment Information	18. SEGMENT INFORMATION The Company has three operating and reportable segments: Assessment, Permitting and Response, Measurement and Analysis and Remediation and Reuse. These segments are monitored separately by management for performance against budget and prior year and are consistent with internal financial reporting. The Company’s operating segments are organized based upon primary services provided, the nature of the production process, their type of customers, methods used to distribute the products and the nature of the regulatory environment. Segment Adjusted EBITDA is the primary measure of operating performance for all three operating segments. Segment Adjusted EBITDA is the calculated Co mpany’s Earnings before Interest, Tax, Depreciation and Amortization (“EBITDA”), adjusted to exclude certain transactions such as stock-based compensation, acquisition costs and fair value changes in financial instruments, amongst others. Beginning in the first quarter of 2023, the calculation of Segment adjusted EBITDA no longer adjusts for start-up losses and investment in new services as the Chief Operating Decision Maker (“CODM”) no longer reviews the Segment Adjusted EBITDA measure without these costs. The CODM does not review segment assets as a measure of segment performance. During the first quarter of 2023, the Company determined to sell one of its specialty service lines within the lab testing business (the "Discontinuing Specialty Lab"), whose performance has been sporadic and whose service offering is non-core to the Company’s business. The Company expects the sale process to be completed by December 31, 2023. The discontinuation of this specialty service line, which is part of the Company's Measurement and Analysis segment, did not represent a strategic shift that had (or will have) a major effect on the Company’s operations and financial results, therefore it did not meet the requirements to be classified as discontinued operations. Corporate and Other includes costs associated with general corporate overhead (including executive, legal, finance, safety, human resources, marketing and IT related costs) that are not directly related to supporting operations. Overhead costs that are directly related to supporting operations (such as insurance, software, licenses, shared services and payroll processing costs) are allocated to the operating segments on a basis that reasonably approximates an estimate of the use of these services. Segment revenues and Adjusted EBITDA consisted of the following: Three Months Ended March 31, 2023 2022 Segment Segment Segment Adjusted Segment Adjusted Revenues EBITDA Revenues EBITDA (3) Assessment, Permitting and Response $ 52,214 $ 14,266 $ 45,600 $ 9,623 Measurement and Analysis 42,527 (1) 6,387 39,761 (1) 6,322 (2) Remediation and Reuse 36,687 5,278 49,319 7,993 Total Operating Segments 131,428 25,931 134,680 23,938 Corporate and Other — ( 9,328 ) — ( 7,487 ) Total $ 131,428 $ 16,603 $ 134,680 $ 16,451 _____________________________________ (1) Includes revenue of $ 1.4 million and $ 5.6 million from the Discontinuing Specialty Lab, for the three months ended March 31, 2023 and March 31, 2022, respectively. Includes Adjusted EBITDA of $ 1.3 million from the Discontinuing Specialty Lab. (3) Includes the add back of start-up losses and investment in new services of $ 0.8 million. Presented below is a reconciliation of the Company’s segment measure to net loss: For the Three Months 2023 2022 Total $ 16,603 $ 16,451 Interest expense, net ( 1,541 ) ( 1,092 ) Income tax expense ( 1,367 ) ( 1,269 ) Depreciation and amortization ( 10,555 ) ( 12,144 ) Stock-based compensation ( 13,035 ) ( 10,425 ) Start-up losses and investment in new services — ( 786 ) Acquisition costs ( 775 ) ( 467 ) Fair value changes in financial instruments ( 1,873 ) 2,449 Fair value changes in business acquisition 398 21 Expenses related to financing transactions ( 4 ) ( 7 ) Discontinuing Specialty Lab ( 2,436 ) (1) — Other losses or expenses ( 134 ) ( 267 ) Net loss $ ( 14,719 ) $ ( 7,536 ) __________________________ (1) Amounts consist of operating losses before depreciation related to the Discontinuing Specialty Lab .

Related-Party Transactions

Related-Party Transactions	3 Months Ended
	Mar. 31, 2023
Related Party Transactions [Abstract]
Related-Party Transactions	19. RELATED-PARTY TRANSACTIONS The Company did no t have any related party transactions during the three months ended March 31, 2023 and March 31, 2022 .

Defined Contribution Plan

Defined Contribution Plan	3 Months Ended
	Mar. 31, 2023
Retirement Benefits [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, 2023, and December 31, 2022 , 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. 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 5.0 % of the participant’s compensation. Employer contributions under the 401(k) Savings Plan w ere $ 2.1 million and $ 1.7 million for the three months ended March 31, 2023 and March 31, 2022, respectively, and are included within selling, general, and administrative expense on the unau dited condensed consolidated statements of operations.

Subsequent Events

Subsequent Events	3 Months Ended
	Mar. 31, 2023
Subsequent Events [Abstract]
Subsequent Events	21. SUBSEQUENT EVENTS Business Acquisitions —On May 1, 2023, the Company completed the business acquisition of GreenPath Energy LTD ("GreenPath") by acquiring 100.0 % of its common stock. GreenPath is a leading optical gas imaging and fugitive emissions management services firm and is based in Calgary, Canada. On April 28, 2023, the Company signed an arrangement agreement which provides for the acquisition of Matrix Solutions, Inc. ("Matrix") by acquiring 100.0 % of its common stock. Matrix is one of Canada’s leading environmental and engineering consulting companies and is based in Calgary, Canada. This business acquisition is expected to close by the end of the second quarter 2023. These transactions qualify as business acquisitions and will be accounted for as business combinations. The following table summarizes the main elements of the purchase price of these acquisitions: Total Cash Common Stock Purchase Price GreenPath $ 16,580 (1) 3,520 $ 20,100 Matrix 65,191 (2) — 65,191 _________________________________________ The cash portion of this acquisition's purchase price was funded through cash on hand. (2) Upon closing, the cash portion of this acquisition's purchase price will funded through a combination of cash on hand and proceeds received from our revolving credit facility.

Description of the Business a_2

Description of the Business and Basis of Presentation (Policies)	3 Months Ended
	Mar. 31, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation —The unaudited condensed consolidated financial statements include the operations of the Company and its wholly-owned subsidiaries. These unaudited condensed consolidated financial statements are presented in conformity with accounting principles generally accepted in the United States (“U.S. GAAP”) and have been prepared pursuant to the rules and regulations of the U.S. Securities and Exchange Commission (“SEC”) that permit reduced disclosure for interim periods. The unaudited condensed consolidated financial statements include all accounts of the Company and, in the opinion of management, include all recurring adjustments and normal accruals necessary for a fair statement of the Company’s financial position, results of operations and cash flows for the dates and periods presented. These unaudited condensed consolidated financial statements should be read in conjunction with the Company’s audited financial statements as of and for the year ended December 31, 2022 . Results for interim periods are not necessarily indicative of the results to be expected during the remainder of the current year or for any future period. All intercompany transactions, accounts and profits, have been eliminated in the unaudited condensed consolidated financial statements.
Recently Adopted Accounting Pronouncements /Recently Issued Accounting Pronouncements Not Yet Adopted	Recently Adopted Accounting Pronouncements —In A ugust 2020, the Financial Accounting Standards Board ("FASB") issued Accounting Standard Update ("ASU") 2020-06, Debt—Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging—Contracts in Entity’s Own Equity (Subtopic 815-40)—Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity. The ASU simplifies accounting for convertible instruments by removing major separation models required under current U.S. GAAP. Consequently, more convertible debt instruments will be reported as a single liability instrument with no separate accounting for embedded conversion features. The ASU removes certain settlement conditions that are required for equity contracts to qualify for the derivative scope exception, which will permit more equity contracts to qualify for the exception. The ASU also simplifies the diluted net income per share calculation in certain areas. The new guidance was adopted as of January 1, 2022 and did not have a material impact on the Company’s unaudited condensed consolidated financial statements. In October 2021, the FASB issued ASU No. 2021-08, Business Combinations (Topic 805): Accounting for Contract Assets and Contract Liabilities from Contracts with Customers. Under the new guidance (ASC 805-20-30-28), the acquirer should determine what contract assets and/or contract liabilities it would have recorded under ASC 606 (the revenue guidance) as of the acquisition date, as if the acquirer had entered into the original contract at the same date and on the same terms as the acquiree. The new guidance was adopted as of January 1, 2023 and did not have a material impact on the Company’s unaudited condensed consolidated financial statements; however it may impact the accounting for future acquisitions. The future impact of this new guidance will be primarily a function of the facts and circumstances specific to any acquisitions consummated after adoption and therefore cannot be predicted.

Revenues and Accounts Receiva_2

Revenues and Accounts Receivable (Tables)	3 Months Ended
	Mar. 31, 2023
Revenues And Accounts Receivable [Abstract]
Schedule of Contract Balances	The following table presents the Company’s contract balances: March 31, December 31, 2023 2022 Contract assets $ 53,563 $ 52,403 Contract liabilities 10,932 18,549
Schedule of Accounts Receivable, Net	Accounts Receivable, Net Accounts receivable, net consisted of the following: March 31, December 31, Accounts receivable, invoiced $ 87,261 $ 95,055 Accounts receivable, other 503 1,571 Allowance for doubtful accounts ( 2,292 ) ( 1,915 ) Accounts receivable—net $ 85,472 $ 94,711
Schedule of Allowance for Doubtful Accounts	The allowance for doubtful accounts consisted of the following: Beginning Bad Debt Charged to Other (1) Ending There months ended March 31, 2023 $ 1,915 $ 444 $ ( 67 ) $ — $ 2,292 Year ended December 31, 2022 4,581 ( 1,097 ) ( 1,696 ) 127 1,915 ____________________ (1) This amount consists of additions to the allowance due to business acquisitions.

Prepaid and Other Current Ass_2

Prepaid and Other Current Assets (Tables)	3 Months Ended
	Mar. 31, 2023
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Schedule of Prepaid and Other Current Assets	Prepaid and other current assets consisted of the following: March 31, December 31, 2023 2022 Deposits $ 1,366 $ 1,394 Prepaid expenses 9,167 5,266 Supplies 4,074 3,632 Income tax receivable 571 694 Prepaid and other current assets $ 15,178 $ 10,986

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	3 Months Ended
	Mar. 31, 2023
Property, Plant and Equipment [Abstract]
Property and Equipment, Net	Property and equipment, net, consisted of the following: Estimated March 31, December 31, Useful Life 2023 2022 Lab and test equipment 7 years $ 22,992 $ 21,171 Vehicles 5 years 5,841 5,732 Equipment 3 - 7 years 42,819 40,940 Furniture and fixtures 7 years 2,853 2,841 Leasehold improvements 7 years 8,837 8,576 Aircraft 10 years — 931 Building 39 years 6,112 2,975 89,454 83,166 Land 725 725 Construction in progress 3,092 3,150 Less accumulated depreciation ( 52,586 ) ( 50,996 ) Total property and equipment— $ 40,685 $ 36,045

Leases (Tables)

Leases (Tables)	3 Months Ended
	Mar. 31, 2023
Leases [Abstract]
Summary of Components of Lease Expense	The components of lease expense were as follows: For the Three Months Ended March 31, Statement of Operations Location 2023 2022 Operating lease cost Lease cost Selling, general and administrative expense $ 2,741 $ 2,451 Variable lease cost Selling, general and administrative expense 326 367 Total operating lease cost 3,067 2,818 Finance lease cost Amortization of right of use assets Depreciation and amortization 1,154 939 Interest on lease liabilities Interest expense—net 130 112 Total finance lease cost 1,284 1,051 Total lease cost $ 4,351 $ 3,869
Summary of Supplemental Cash Flow Information Related To Leases	Supplemental cash flows information related to leases was as follows: For the Three Months Ended March 31, 2023 2022 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows used in operating leases $ 2,557 $ 2,302 Operating cash flows used in finance leases 130 112 Financing cash flows used in finance leases 1,029 944 Lease liabilities arising from new ROU assets: Operating leases 7,999 8,815 Finance leases 2,405 512
Summary of Weighted Average Remaining Lease Terms and Weighted Average Discount Rates	Weighted average remaining lease terms and weighted average discount rates were: March 31, 2023 Operating Leases Finance Leases Weighted average remaining lease term (years) 4.62 3.43 Weighted average discount rate 3.31 % 5.57 % March 31, 2022 Operating Leases Finance Leases Weighted average remaining lease term (years) 4.86 3.03 Weighted average discount rate 2.50 % 4.98 %
Schedule of Maturities of Lease Liabilities	The following is a schedule by year of the maturities of lease liabilities with original terms in excess of one year: Operating Leases Finance Leases Remainder of 2023 $ 7,117 $ 3,657 2024 8,554 3,543 2025 6,507 2,612 2026 5,006 1,902 2027 3,385 967 2028 and thereafter 4,787 135 Total undiscounted future minimum lease payments 35,356 12,816 Less imputed interest ( 2,693 ) ( 1,179 ) Total discounted future minimum lease payments $ 32,663 $ 11,637

Business Acquisitions (Tables)

Business Acquisitions (Tables)	3 Months Ended
	Mar. 31, 2023
Business Acquisition [Line Items]
Summary of Supplemental Unaudited Pro-Forma Information	The unaudited condensed consolidated financial information summarized in the following table gives effect to the 2023 and the 2022 acquisitions discussed above assuming they occurred on January 1, 2022. These unaudited consolidated pro forma operating results do not assume any impact from revenue, cost or other operating synergies that are expected or may have been realized as a result of the acquisitions. These unaudited consolidated pro forma operating results are presented for illustrative purposes only and are not indicative of the operating results that would have been achieved had the acquisitions occurred on January 1, 2022, nor does the information purport to reflect results for any future period. For the Three Months Ended March 31, 2023 2022 As Acquisitions Consolidated As Acquisitions Consolidated Revenues $ 131,428 $ 433 $ 131,861 $ 134,680 $ 5,625 $ 140,305 Net (loss) income ( 14,719 ) ( 67 ) ( 14,786 ) ( 7,536 ) 722 ( 6,814 )
Frontier and EAI
Business Acquisition [Line Items]
Summary of Main Elements of Purchase Price of Acquisitions	The following table summarizes the elements of the purchase price of the acquisitions completed during the three months ended March 31, 2023: Cash Common Other Contingent Total Frontier $ 1,146 $ — $ — $ — $ 1,146 EAI 5,390 — ( 342 ) 25 5,073 Total $ 6,536 $ — $ ( 342 ) $ 25 $ 6,219
Summary of Purchase Price Attributable to Acquisitions	The preliminary purchase price attributable to the acquisitions was allocated as follows: Frontier EAI Total (1) Cash $ — $ 11 $ 11 Accounts receivable — 1,502 1,502 Other current assets — 121 121 Current assets — 1,634 1,634 Property and equipment 302 191 493 Customer relationships — 1,402 1,402 Trade names — 106 106 Covenants not to compete — 263 263 Goodwill 844 1,965 2,809 Total assets 1,146 5,561 6,707 Current liabilities — 488 488 Total liabilities — 488 488 Purchase price $ 1,146 $ 5,073 $ 6,219

Goodwill and Intangible Assets

Goodwill and Intangible Assets (Tables)	3 Months Ended
	Mar. 31, 2023
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Amounts Related to Goodwill	Amounts related to goodwill are as follows: Assessment, Measurement Remediation Total Balance as of December 31, 2022 $ 185,116 $ 86,205 $ 52,547 $ 323,868 Goodwill acquired during the period — 844 1,965 2,809 Acquisitions measurement period adjustments ( 169 ) ( 10 ) — ( 179 ) Balance as of March 31, 2023 $ 184,947 $ 87,039 $ 54,512 $ 326,498
Schedule of Amounts Related to Finite-Lived Intangible Assets	Amounts related to finite-lived intangible assets are as follows: March 31, 2023 Estimated Gross Accumulated Total Finite lived intangible assets Customer relationships 2 - 15 years $ 209,426 $ 100,404 $ 109,022 Covenants not to compete 4 - 5 years 33,805 29,020 4,785 Trade names 1 - 5 years 22,167 18,708 3,459 Proprietary software 3 - 5 years 23,324 16,942 6,382 Patent 16 years 17,479 3,856 13,623 Total other intangible assets $ 306,201 $ 168,930 $ 137,271 December 31, 2022 Estimated Gross Accumulated Total Finite lived intangible assets Customer relationships 2 - 15 years $ 208,024 $ 95,768 $ 112,256 Covenants not to compete 4 - 5 years 33,542 28,280 5,262 Trade names 1 - 5 years 22,061 18,256 3,805 Proprietary software 3 - 5 years 22,698 15,810 6,888 Patent 16 years 17,479 3,583 13,896 Total other intangible assets $ 303,804 $ 161,697 $ 142,107
Schedule of Future Amortization Expense	Future amortization expense is estimated to be as follows for each of the five following years and thereafter: December 31, 2023 (remaining) 20,920 2024 24,607 2025 17,727 2026 13,952 2027 13,429 Thereafter 46,636 Total $ 137,271

Accounts Payable and Other Ac_2

Accounts Payable and Other Accrued Liabilities (Tables)	3 Months Ended
	Mar. 31, 2023
Payables and Accruals [Abstract]
Summary of Accounts Payable and Other Accrued Liabilities	Accounts payable and other accrued liabilities consisted of the following: March 31, December 31, 2023 2022 Accounts payable $ 24,399 $ 25,353 Accrued expenses 16,311 14,754 Other business acquisitions purchase 450 1,185 Contract liabilities 10,932 18,549 Other current liabilities 3,328 3,571 Total accounts payable and $ 55,420 $ 63,412

Accrued Payroll and Benefits (T

Accrued Payroll and Benefits (Tables)	3 Months Ended
	Mar. 31, 2023
Statement of Financial Position [Abstract]
Schedule of Accrued Payroll and Benefits	Accrued payroll and benefits consisted of the following: March 31, December 31, 2023 2022 Accrued bonuses $ 3,559 $ 8,624 Accrued paid time off 1,161 1,088 Accrued payroll 9,084 8,410 Accrued other 2,548 2,406 Total accrued payroll and benefits $ 16,352 $ 20,528

Debt (Tables)

Debt (Tables)	3 Months Ended
	Mar. 31, 2023
Debt Disclosure [Abstract]
Schedule of Debt	Debt consisted of the following: March 31, December 31, 2023 2022 Term loan facility $ 164,062 $ 166,250 Revolving line of credit — — Less deferred debt issuance costs ( 1,595 ) ( 1,725 ) Total debt 162,467 164,525 Less current portion of long-term debt ( 13,125 ) ( 12,031 ) Long-term debt, less current portion $ 149,342 $ 152,494
Summary of Term Loan Amortization	The 2021 Credit Facility term loan must be repaid in quarterly installments and shall amortize at the following future quarterly rates: Date Quarterly Installment Rate June 30, 2023 1.25 % September 30, 2023 1.25 % December 31, 2023 1.88 % March 31, 2024 1.88 % June 30, 2024 1.88 % September 30, 2024 1.88 % December 31, 2024 1.88 % March 31, 2025 1.88 % June 30, 2025 1.88 % September 30, 2025 1.88 % December 31, 2025 2.50 % March 31, 2026 2.50 % April 27, 2026 Remaining balance
Summary of 2021 Credit Facility Interest Rate Subject to Leverage Ratio and LIBOR	The 2021 Credit Facility term loan and the revolver bear interest subject to the Company’s leverage ratio and LIBOR as follows: Pricing Tier Consolidated Senior Credit Facilities Senior Credit Facilities Commitment Letter of Credit Fee 1 ≥ 3.75 x to 1.0 2.50 % 1.50 % 0.25 % 2.50 % 2 < 3.75 x to 1.0 but ≥ 3.25 to 1.0 2.25 1.25 0.23 2.25 3 < 3.25 x to 1.0 but ≥ 2.50 to 1.0 2.00 1.00 0.20 2.00 4 < 2.50 x to 1.0 but ≥ 1.75 to 1.0 1.75 0.75 0.15 1.75 5 < 1.75 x to 1.0 1.50 0.50 0.15 1.50
Schedule of Aggregate Annual Maturities of Long-Term Debt	The following is a schedule of the aggregate annual maturities of long-term debt presented on the unaudited condensed consolidated statement of financial position, based on the terms of the 2021 Credit Facility: March 31, 2024 $ 13,125 2025 13,125 2026 15,312 2027 122,500 2028 — Total $ 164,062

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2023
Fair Value Disclosures [Abstract]
Summary of Financial Instruments Measured at Fair Value on Recurring Basis	The following financial instruments are measured at fair value on a recurring basis using significant unobservable inputs (Level 3): March 31, December 31, 2023 2022 Interest rate swap (1) $ 5,078 $ 6,046 Total assets $ 5,078 $ 6,046 Business acquisitions contingent consideration, $ 4,734 $ 3,801 Business acquisitions contingent consideration, 3,121 4,454 Conversion option 26,636 25,731 Total liabilities $ 34,491 $ 33,986 _____________________________ (1) Included in other assets in the unaudited condensed consolidated statement of financial position. The estimated fair value amounts shown above are not necessarily indicative of the amounts that the Company would realize upon disposition, nor do they indicate the Company’s intent or ability to dispose of the financial instrument. The following table sets forth the Company’s financial instruments that were measured at fair value on a recurring basis: Interest Total Business Business Conversion Total Balance—at January 1, 2022 $ — $ — $ 31,450 $ 4,350 $ 23,081 $ 58,881 Acquisitions — — — 1,216 — 1,216 Changes in fair value included in earnings 3,005 3,005 ( 21 ) — 556 535 Payment of contingent consideration — — ( 30,000 ) — — ( 30,000 ) Balance—at March 31, 2022 $ 3,005 $ 3,005 $ 1,429 $ 5,566 $ 23,637 $ 30,632 Balance—at January 1, 2023 $ 6,046 $ 6,046 $ 3,801 $ 4,454 $ 25,731 $ 33,986 Acquisitions — — 25 — — 25 Changes in fair value included in earnings ( 968 ) ( 968 ) ( 515 ) 117 905 507 Payment of contingent consideration — — ( 27 ) — — ( 27 ) Reclass of long term to short term — — 1,450 ( 1,450 ) — — Balance—at March 31, 2023 $ 5,078 $ 5,078 $ 4,734 $ 3,121 $ 26,636 $ 34,491

Stockholder's Equity (Tables)

Stockholder's Equity (Tables)	3 Months Ended
	Mar. 31, 2023
Summary of Issued Shares of Common Stock	The Co mpany issued the following shares of common stock: Three Months Ended March 31, 2023 2022 Shares Average Price per Share Total Shares Average Price per Share Total Exercise of options 124,455 $ 21.61 $ 2,690 30,607 $ 14.03 $ 429 Restricted shares, net (1) 90,116 36.81 — 25,289 66.58 — Total 214,571 $ 27.99 $ 2,690 55,896 $ 37.81 $ 429 (1) Represents the non-cash release of common shares due to the vesting of restricted stock.
Schedule of Share Authorized to be Issue and Available for Grant	The following number of shares were authorized to be issued and available for grant: March 31, 2023 2017 Plan 2013 Plan Total Shares authorized to be issued 6,329,913 2,037,019 8,366,932 Shares available for grant (1) 893,522 — 893,522 March 31, 2022 2017 Plan 2013 Plan Total Shares authorized to be issued 8,272,487 1,904,644 10,177,131 Shares available for grant (1) 577,139 — 577,139 (1) In January 2023 and January 2022 the Board of Directors ratified the addition of 1,189,801 and 1,185,112 shares of common stock, respectively, to the number of shares available for issuance under the 2017 Plan pursuant to the annual increase provision of such plan. Unless the Board of Directors determines otherwise, additional annual increases will be effective on each January 1, through January 1, 2027. The 2017 Plan permits the company to settle awards, if and when vested, in cash at its discretion. Pursuant to the terms of the 2017 Plan, the number of shares authorized for issuance thereunder will only be reduced with respect to shares of common stock actually issued upon exercise or settlement of an award. Shares of common stock subject to awards that have been canceled, expired, forfeited or otherwise not issued under an award and shares of common stock subject to awards settled in cash do not count as shares of common stock issued under the 2017 Plan. Shares available for grant exclude awards of stock appreciation rights approved in December 2021 that are subject to vesting based on the achievement of certain market conditions, which have not yet been, and may not be, a chieved. See footnote 1 to the table in Common Stock Reserved for Future Issuance below for additional information on stock appreciation rights.
Schedule of Stock Compensation Expense	Total stock compensation expense for the Plans was as follows: Three Months Ended March 31, 2023 2022 2017 plan 2013 2017 plan 2013 Options Restricted SARs Options Total Options Restricted SARs Options Total Cost of revenue $ 349 $ 543 $ — $ — $ 892 $ 294 $ — $ — $ — $ 294 Selling, general and 1,724 8,154 2,265 — 12,143 1,979 5,792 2,360 — 10,131 Total $ 2,073 $ 8,697 $ 2,265 $ — $ 13,035 $ 2,273 $ 5,792 $ 2,360 $ — $ 10,425
Summary of Performance Hurdles	The performance hurdles are as follows: SARs Stock Price Performance Hurdle Portion of SARs Subject to Performance Hurdle $ 133.58 1/3 $ 166.98 1/3 $ 200.37 1/3
Summary of Weighted Average Assumptions Used in Black-Sholes Option-pricing Model	The following weighted-average assumptions were used in the Black-Sholes option-pricing model calculation: March 31, March 31, 2023 2022 Common stock value (per share) $ 32.16 $ 44.11 Expected volatility 33.79 % 33.45 % Risk-free interest rate 3.72 % 1.74 % Expected life (years) 7.00 6.33 Forfeiture rate None None Dividend rate None None
Schedule of Common Stock Reserved for Future Issuance	The Company has reserved certain stock of its authorized but unissued common stock for possible future issuance in connection with the following: March 31, 2023 2022 Montrose 2013 Stock Incentive Plan 832,519 878,614 Montrose 2017 Stock Incentive Plan (1) 8,722,930 7,893,918 Total 9,555,449 8,772,532 (1) In January 2023 and 2022, the Board of Directors ratified the addition of 1,189,801 and 1,185,112 sha res of common stock, respectively, to the number of shares available for issuance under the 2017 Plan pursuant to the annual increase provision of such plan. Unless the Board of Directors determines otherwise, additional annual increases will be effective on each January 1, through January 1, 2027. The 2017 Plan permits the company to settle awards, if and when vested, in cash at its discretion. Pursuant to the terms of the 2017 Plan, the number of shares authorized for issuance thereunder will only be reduced with respect to shares of common stock actually issued upon exercise or settlement of an award. Shares of common stock subject to awards that have been canceled, expired, forfeited or otherwise not issued under an award and shares of common stock subject to awards settled in cash do not count as shares of common stock issued under the 2017 Plan. The Company expects to have sufficient shares available under the 2017 Plan to satisfy the future settlement of outstanding awards. Shares reserved for future issuance include 3,000,000 shares underlying the 3,000,000 performance SARs granted in December 2021 that are subject to vesting based on the achievement of certain market conditions. Assuming achievement at the highest price performance hurdle, approximately 2,000,000 shares of common stock would be issued upon vesting of these performance SARs. To date, none of the market conditions have been achieved.
Montrose Amended & Restated 2017 Stock Incentive Plan
Schedule of Restricted Stock Activity	RSAs and RSUs activity was as follows: Three Months Ended March 31, 2023 2022 Shares Average Price per Share Fair Value Shares Average Price per Share Fair Value Awards granted 464,186 $ 32.62 $ 15,140 106,324 $ 46.82 $ 4,978
Summary of Stock Option Activity	The following summarizes the options activity of the 2017 Plan: Options to Weighted- Weighted Weighted Aggregate Outstanding as of January 1, 2022 2,036,729 $ 26 $ 14 8.30 $ 91,030 Granted 547,884 44 16 — — Forfeited/ cancelled ( 23,082 ) 36 — — — Exercised ( 11,547 ) 27 — — 313 Outstanding as of March 31, 2022 2,549,984 30 14 8.46 59,955 Outstanding as of January 1, 2023 2,579,566 $ 31 $ 15 7.76 $ 37,292 Granted 233,955 32 14 — — Forfeited/ cancelled ( 34,619 ) 35 — — — Exercised ( 101,279 ) 25 — — 2,467 Outstanding as of March 31, 2023 2,677,623 $ 31 $ 15 7.78 $ 21,127 Exercisable at March 31, 2023 1,305,511 29 — 7.19 11,880
Montrose Amended and Restated 2013 Stock Option Plan
Summary of Stock Option Activity	The following summarizes the activity of the 2013 Plan: Options to Weighted- Weighted Weighted Aggregate Outstanding as of January 1, 2022 897,674 $ 6 $ 2 4.37 $ 57,529 Exercised ( 19,060 ) 6 — — 821 Outstanding as of March 31, 2022 878,614 6 2 4.13 40,860 Outstanding as of January 1, 2023 855,695 $ 6 $ 2 3.31 $ 32,478 Exercised ( 23,176 ) 9 — — 963 Outstanding as of March 31, 2023 832,519 $ 6 $ 2 3.03 $ 24,393 Exercisable at March 31, 2023 832,519 6 — 3.03 24,393

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	3 Months Ended
	Mar. 31, 2023
Earnings Per Share [Abstract]
Computation of Basic and Diluted Net Loss Per Share Attributable to Common Stockholders	The following table summarizes the computation of basic and diluted net loss per share attributable to common stockholders of the Company: Three Months Ended March 31, (In thousands, except for net loss per share) 2023 2022 Net loss $ ( 14,719 ) $ ( 7,536 ) Convertible and redeemable series A-2 preferred ( 4,100 ) ( 4,100 ) Net loss attributable to common stockholders ( 18,819 ) ( 11,636 ) Weighted-average common shares outstanding – 29,857 29,662 Net loss per share attributable to common $ ( 0.63 ) $ ( 0.39 )
Common Stock Equivalents Excluded from Calculation of Diluted Loss Per Share Attributable to Common Stockholders	The following common stock equivalents were excluded from the calculation of diluted net loss per share attributable to common stockholders because their effect would have been anti-dilutive: March 31, 2023 (1) 2022 (1) Stock options 3,510,142 2,034,041 Restricted stock 2,151,785 1,777,958 Series A-2 4,735,220 4,329,640 SARs 3,000,000 3,000,000 _____________________________ (1) Includes 7,362,459 and 5,008,269 common stock equivalents that are out of the money as of March 31, 2023 and March 31, 2022 , respectively.

Segment Information (Tables)

Segment Information (Tables)	3 Months Ended
	Mar. 31, 2023
Segment Reporting [Abstract]
Components of Segment Revenues and Adjusted EBITDA	Segment revenues and Adjusted EBITDA consisted of the following: Three Months Ended March 31, 2023 2022 Segment Segment Segment Adjusted Segment Adjusted Revenues EBITDA Revenues EBITDA (3) Assessment, Permitting and Response $ 52,214 $ 14,266 $ 45,600 $ 9,623 Measurement and Analysis 42,527 (1) 6,387 39,761 (1) 6,322 (2) Remediation and Reuse 36,687 5,278 49,319 7,993 Total Operating Segments 131,428 25,931 134,680 23,938 Corporate and Other — ( 9,328 ) — ( 7,487 ) Total $ 131,428 $ 16,603 $ 134,680 $ 16,451 _____________________________________ (1) Includes revenue of $ 1.4 million and $ 5.6 million from the Discontinuing Specialty Lab, for the three months ended March 31, 2023 and March 31, 2022, respectively. Includes Adjusted EBITDA of $ 1.3 million from the Discontinuing Specialty Lab. (3) Includes the add back of start-up losses and investment in new services of $ 0.8 million.
Reconciliation of Segment Measure to Net Loss	Presented below is a reconciliation of the Company’s segment measure to net loss: For the Three Months 2023 2022 Total $ 16,603 $ 16,451 Interest expense, net ( 1,541 ) ( 1,092 ) Income tax expense ( 1,367 ) ( 1,269 ) Depreciation and amortization ( 10,555 ) ( 12,144 ) Stock-based compensation ( 13,035 ) ( 10,425 ) Start-up losses and investment in new services — ( 786 ) Acquisition costs ( 775 ) ( 467 ) Fair value changes in financial instruments ( 1,873 ) 2,449 Fair value changes in business acquisition 398 21 Expenses related to financing transactions ( 4 ) ( 7 ) Discontinuing Specialty Lab ( 2,436 ) (1) — Other losses or expenses ( 134 ) ( 267 ) Net loss $ ( 14,719 ) $ ( 7,536 ) __________________________ (1) Amounts consist of operating losses before depreciation related to the Discontinuing Specialty Lab .

Subsequent Events (Tables)

Subsequent Events (Tables)	3 Months Ended
	Mar. 31, 2023
Matrix
Subsequent Event [Line Items]
Summary of Main Elements of Purchase Price of Acquisitions	The following table summarizes the main elements of the purchase price of these acquisitions: Total Cash Common Stock Purchase Price GreenPath $ 16,580 (1) 3,520 $ 20,100 Matrix 65,191 (2) — 65,191 _________________________________________ The cash portion of this acquisition's purchase price was funded through cash on hand. (2) Upon closing, the cash portion of this acquisition's purchase price will funded through a combination of cash on hand and proceeds received from our revolving credit facility.

Description of the Business a_3

Description of the Business and Basis of Presentation - Additional Information (Details)	3 Months Ended
	Mar. 31, 2023 Employee Office Segment
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Entity formation, month and year	2013-11
Number of offices in which entity operates | Office	80
Entity number of employees | Employee	3,000
Number of operating segments | Segment	3

Summary of New Accounting Pro_2

Summary of New Accounting Pronouncements - Additional Information (Details)	Mar. 31, 2023
Accounting Standards Update 2020-06
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Change in accounting principle, accounting standards update, adopted	true
Change in accounting principle, accounting standards update, adoption date	Jan. 01, 2022
Change in accounting principle, accounting standards update, immaterial effect	true
Accounting Standards Update 2021-08
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Change in accounting principle, accounting standards update, adopted	true
Change in accounting principle, accounting standards update, adoption date	Jan. 01, 2023
Change in accounting principle, accounting standards update, immaterial effect	true

Revenues and Accounts Receiva_3

Revenues and Accounts Receivable - Schedule of Contract Balances (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Revenues And Accounts Receivable [Abstract]
Contract assets	$ 53,563	$ 52,403
Contract liabilities	$ 10,932	$ 18,549

Revenues and Accounts Receiva_4

Revenues and Accounts Receivable - Additional Information (Details)	3 Months Ended		12 Months Ended
	Mar. 31, 2023 USD ($) Customer	Mar. 31, 2022 Customer	Dec. 31, 2022 USD ($) Customer
Accounts Notes And Loans Receivable [Line Items]
Contracts assets acquired through business acquisitions	$ 200,000		$ 1,700,000
Contract liabilities acquired through business acquisitions	0		0
Contract with customer liabilities, revenue recognized	12,800,000
Revenue remaining performance obligations	$ 98,200,000		$ 100,400,000
Customer Concentration Risk | Accounts Receivable | Significant Customer
Accounts Notes And Loans Receivable [Line Items]
Concentration risk percentage	10%		10%
Number of customers | Customer	0		0
Customer Concentration Risk | Revenue | Significant Customer
Accounts Notes And Loans Receivable [Line Items]
Concentration risk percentage	10%	17.30%
Number of customers | Customer	0	1

Revenues and Accounts Receiva_5

Revenues and Accounts Receivable - Additional Information (Details1) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue remaining performance obligations	$ 98.2	$ 100.4
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2023-04-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue remaining performance obligations	$ 79.1
Revenue remaining performance obligations, satisfaction period	9 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2024-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue remaining performance obligations	$ 19.1
Revenue remaining performance obligations, satisfaction period

Revenues and Accounts Receiva_6

Revenues and Accounts Receivable - Schedule of Accounts Receivable, Net (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Revenues And Accounts Receivable [Abstract]
Accounts receivable, invoiced	$ 87,261	$ 95,055
Accounts receivable, other	503	1,571
Allowance for doubtful accounts	(2,292)	(1,915)	$ (4,581)
Accounts receivable—net	$ 85,472	$ 94,711

Revenues and Accounts Receiva_7

Revenues and Accounts Receivable - Schedule of Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands		3 Months Ended		12 Months Ended
		Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Revenues And Accounts Receivable [Abstract]
Beginning Balance		$ 1,915	$ 4,581	$ 4,581
Bad Debt Expense (Recovery)		444	$ (528)	(1,097)
Charged to Allowance		(67)		(1,696)
Other	[1]	0		127
Ending Balance		$ 2,292		$ 1,915
[1] This amount consists of additions to the allowance due to business acquisitions.

Prepaid and Other Current Ass_3

Prepaid and Other Current Assets - Schedule of Prepaid and Other Current Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Deposits	$ 1,366	$ 1,394
Prepaid expenses	9,167	5,266
Supplies	4,074	3,632
Income tax receivable	571	694
Prepaid and other current assets	$ 15,178	$ 10,986

Property and Equipment, Net - P

Property and Equipment, Net - Property and Equipment, Net (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Dec. 31, 2022
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 89,454	$ 83,166
Less accumulated depreciation	(52,586)	(50,996)
Total property and equipment— net	$ 40,685	36,045
Lab and test equipment
Property Plant And Equipment [Line Items]
Estimated Useful Life	7 years
Property and equipment, gross	$ 22,992	21,171
Vehicles
Property Plant And Equipment [Line Items]
Estimated Useful Life	5 years
Property and equipment, gross	$ 5,841	5,732
Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 42,819	40,940
Equipment | Minimum
Property Plant And Equipment [Line Items]
Estimated Useful Life	3 years
Equipment | Maximum
Property Plant And Equipment [Line Items]
Estimated Useful Life	7 years
Furniture and fixtures
Property Plant And Equipment [Line Items]
Estimated Useful Life	7 years
Property and equipment, gross	$ 2,853	2,841
Leasehold improvements
Property Plant And Equipment [Line Items]
Estimated Useful Life	7 years
Property and equipment, gross	$ 8,837	8,576
Aircraft
Property Plant And Equipment [Line Items]
Estimated Useful Life	10 years
Property and equipment, gross		931
Building
Property Plant And Equipment [Line Items]
Estimated Useful Life	39 years
Property and equipment, gross	$ 6,112	2,975
Land
Property Plant And Equipment [Line Items]
Property and equipment, gross	725	725
Construction in Progress
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 3,092	$ 3,150

Property and Equipment, Net - A

Property and Equipment, Net - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Property Plant And Equipment [Line Items]
Depreciation expense	$ 2.2	$ 1.8

Leases - Additional Information

Leases - Additional Information (Details)	3 Months Ended
	Mar. 31, 2023
Minimum
Lessee Lease Description [Line Items]
Lessee operating and finance lease term	1 year
Maximum
Lessee Lease Description [Line Items]
Lessee operating and finance lease term	15 years

Leases - Summary of Components

Leases - Summary of Components of Lease Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Lessee Lease Description [Line Items]
Total operating lease cost	$ 3,067	$ 2,818
Total finance lease cost	1,284	1,051
Total lease cost	4,351	3,869
Selling, General and Administrative Expenses
Lessee Lease Description [Line Items]
Lease cost	2,741	2,451
Variable lease cost	326	367
Depreciation and Amortization
Lessee Lease Description [Line Items]
Amortization of right of use assets	1,154	939
Interest Expense, Net
Lessee Lease Description [Line Items]
Interest on lease liabilities	$ 130	$ 112

Leases - Summary of Supplementa

Leases - Summary of Supplemental Cash Flow Information Related To Leases (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Leases [Abstract]
Operating cash flows used in operating leases	$ 2,557	$ 2,302
Operating cash flows used in finance leases	130	112
Financing cash flows used in finance leases	1,029	944
Operating leases	7,999	8,815
Finance leases	$ 2,405	$ 512

Leases - Summary of Weighted Av

Leases - Summary of Weighted Average Remaining Lease Terms and Weighted Average Discount Rates (Details)	Mar. 31, 2023	Mar. 31, 2022
Leases [Abstract]
Weighted average remaining lease term, Operating Leases	4 years 7 months 13 days	4 years 10 months 9 days
Weighted average remaining lease term, Finance Leases	3 years 5 months 4 days	3 years 10 days
Weighted average discount rate, Operating Leases	3.31%	2.50%
Weighted average discount rate, Finance Leases	5.57%	4.98%

Leases - Summary of Maturities

Leases - Summary of Maturities of Lease Liabilities (Details) $ in Thousands	Mar. 31, 2023 USD ($)
Leases [Abstract]
Operating Leases, Remainder of 2023	$ 7,117
Operating Leases, 2024	8,554
Operating Leases, 2025	6,507
Operating Leases, 2026	5,006
Operating Leases, 2027	3,385
Operating Leases, 2028 and thereafter	4,787
Operating Leases, Total undiscounted future minimum lease payments	35,356
Operating Leases, Less imputed interest	(2,693)
Operating Leases, Total discounted future minimum lease payments	32,663
Finance Leases, Remainder of 2023	3,657
Finance Leases, 2024	3,543
Finance Leases, 2025	2,612
Finance Leases, 2026	1,902
Finance Leases, 2027	967
Finance Leases, 2028 and thereafter	135
Finance Leases, Total undiscounted future minimum lease payments	12,816
Finance Leases, Less imputed interest	(1,179)
Finance Leases, Total discounted future minimum lease payments	$ 11,637

Business Acquisitions - Additio

Business Acquisitions - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Feb. 28, 2023	Nov. 30, 2022	Sep. 30, 2022	Aug. 31, 2022	Jan. 31, 2022
Business Acquisition [Line Items]
Transaction costs related to business combinations	$ 775	$ 467
Business combination, paid in cash	6,536
Acquisitions measurement period adjustments	(179)
EnvStd
Business Acquisition [Line Items]
Percentage of interests acquired							100%
EAI
Business Acquisition [Line Items]
Percentage of interests acquired			100%
Business combination, paid in cash	$ 5,390
EAI | Customer Relationships
Business Acquisition [Line Items]
Weighted average useful lives for acquired intangible assets	7 years
EAI | Trade Names
Business Acquisition [Line Items]
Weighted average useful lives for acquired intangible assets	2 years
EAI | Covenants Not to Compete
Business Acquisition [Line Items]
Weighted average useful lives for acquired intangible assets	5 years
Frontier and EAI
Business Acquisition [Line Items]
Revenue	$ 1,000
Pre-tax income (loss)	100
TriAD
Business Acquisition [Line Items]
Percentage of interests acquired						100%
AirKinetics
Business Acquisition [Line Items]
Percentage of interests acquired					100%
Huco
Business Acquisition [Line Items]
Percentage of interests acquired				100%
EnvStd and IAG | 2026 Earn Out
Business Acquisition [Line Items]
Payment through cash or common stock	1,500
Common Stock	5,500
Business combination, earn-out payment, maximum	9,500
Business combination, paid in cash	$ 2,600
EnvStd, IAG, TriAD, AirKinetics and Huco
Business Acquisition [Line Items]
Revenue		3,300
Pre-tax income (loss)		$ 800

Business Acquisitions - Summary

Business Acquisitions - Summary of Elements of Purchase Price of Acquisitions (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2023 USD ($)
Business Acquisition [Line Items]
Cash	$ 6,536
Other Purchase Price Components	(342)
Contingent Consideration	25
Total Purchase Price	6,219
Frontier
Business Acquisition [Line Items]
Cash	1,146
Total Purchase Price	1,146
EAI
Business Acquisition [Line Items]
Cash	5,390
Other Purchase Price Components	(342)
Contingent Consideration	25
Total Purchase Price	$ 5,073

Business Acquisitions - Summa_2

Business Acquisitions - Summary of Purchase Price Attributable to Acquisitions (Details) $ in Thousands	Mar. 31, 2023 USD ($)
Business Acquisition [Line Items]
Cash	$ 11	[1]
Accounts receivable	1,502	[1]
Other current assets	121	[1]
Current assets	1,634	[1]
Property and equipment	493	[1]
Goodwill	2,809	[1]
Total assets	6,707	[1]
Current liabilities	488	[1]
Total liabilities	488	[1]
Purchase price	6,219	[1]
Frontier
Business Acquisition [Line Items]
Property and equipment	302
Goodwill	844
Total assets	1,146
Purchase price	1,146
EAI
Business Acquisition [Line Items]
Cash	11
Accounts receivable	1,502
Other current assets	121
Current assets	1,634
Property and equipment	191
Goodwill	1,965
Total assets	5,561
Current liabilities	488
Total liabilities	488
Purchase price	5,073
Customer Relationships
Business Acquisition [Line Items]
Intangible assets	1,402	[1]
Customer Relationships | EAI
Business Acquisition [Line Items]
Intangible assets	1,402
Trade Names
Business Acquisition [Line Items]
Intangible assets	106	[1]
Trade Names | EAI
Business Acquisition [Line Items]
Intangible assets	106
Covenants Not to Compete
Business Acquisition [Line Items]
Intangible assets	263	[1]
Covenants Not to Compete | EAI
Business Acquisition [Line Items]
Intangible assets	$ 263
[1] The Company is continuing to obtain information to complete the valuation of certain of these acquisitions' assets and liabilities.

Business Acquisitions - Summa_3

Business Acquisitions - Summary of Supplemental Unaudited Pro-Forma Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Business Acquisition [Line Items]
Revenues	$ 131,428	$ 134,680
Net (loss) income	(14,719)	(7,536)
Acquisition Proforma
Business Acquisition [Line Items]
Revenues	433	5,625
Net (loss) income	(67)	722
Consolidated Proforma
Business Acquisition [Line Items]
Revenues	131,861	140,305
Net (loss) income	$ (14,786)	$ (6,814)

Goodwill and Intangible Asset_2

Goodwill and Intangible Assets - Schedule of Amounts Related to Goodwill (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2023 USD ($)
Goodwill [Line Items]
Beginning balance	$ 323,868
Goodwill acquired during the period	2,809
Acquisitions measurement period adjustments	(179)
Ending balance	326,498
Assessment, Permitting and Response
Goodwill [Line Items]
Beginning balance	185,116
Acquisitions measurement period adjustments	(169)
Ending balance	184,947
Measurement and Analysis
Goodwill [Line Items]
Beginning balance	86,205
Goodwill acquired during the period	844
Acquisitions measurement period adjustments	(10)
Ending balance	87,039
Remediation and Reuse Segment
Goodwill [Line Items]
Beginning balance	52,547
Goodwill acquired during the period	1,965
Ending balance	$ 54,512

Goodwill and Intangible Asset_3

Goodwill and Intangible Assets - Schedule of Amounts Related to Finite-Lived Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2023	Dec. 31, 2022
Finite-Lived Intangible Assets [Line Items]
Gross Balance	$ 306,201	$ 303,804
Accumulated Amortization	168,930	161,697
Total Intangible Assets—Net	137,271	142,107
Customer Relationships
Finite-Lived Intangible Assets [Line Items]
Gross Balance	209,426	208,024
Accumulated Amortization	100,404	95,768
Total Intangible Assets—Net	$ 109,022	$ 112,256
Customer Relationships | Minimum
Finite-Lived Intangible Assets [Line Items]
Estimated Useful Life	2 years	2 years
Customer Relationships | Maximum
Finite-Lived Intangible Assets [Line Items]
Estimated Useful Life	15 years	15 years
Covenants Not to Compete
Finite-Lived Intangible Assets [Line Items]
Gross Balance	$ 33,805	$ 33,542
Accumulated Amortization	29,020	28,280
Total Intangible Assets—Net	$ 4,785	$ 5,262
Covenants Not to Compete | Minimum
Finite-Lived Intangible Assets [Line Items]
Estimated Useful Life	4 years	4 years
Covenants Not to Compete | Maximum
Finite-Lived Intangible Assets [Line Items]
Estimated Useful Life	5 years	5 years
Trade Names
Finite-Lived Intangible Assets [Line Items]
Gross Balance	$ 22,167	$ 22,061
Accumulated Amortization	18,708	18,256
Total Intangible Assets—Net	$ 3,459	$ 3,805
Trade Names | Minimum
Finite-Lived Intangible Assets [Line Items]
Estimated Useful Life	1 year	1 year
Trade Names | Maximum
Finite-Lived Intangible Assets [Line Items]
Estimated Useful Life	5 years	5 years
Proprietary Software
Finite-Lived Intangible Assets [Line Items]
Gross Balance	$ 23,324	$ 22,698
Accumulated Amortization	16,942	15,810
Total Intangible Assets—Net	$ 6,382	$ 6,888
Proprietary Software | Minimum
Finite-Lived Intangible Assets [Line Items]
Estimated Useful Life	3 years	3 years
Proprietary Software | Maximum
Finite-Lived Intangible Assets [Line Items]
Estimated Useful Life	5 years	5 years
Patent
Finite-Lived Intangible Assets [Line Items]
Estimated Useful Life	16 years	16 years
Gross Balance	$ 17,479	$ 17,479
Accumulated Amortization	3,856	3,583
Total Intangible Assets—Net	$ 13,623	$ 13,896

Goodwill and Intangible Asset_4

Goodwill and Intangible Assets - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization expense	$ 7.2	$ 9.4

Goodwill and Intangible Asset_5

Goodwill and Intangible Assets - Schedule of Future Amortization Expense (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Goodwill and Intangible Assets Disclosure [Abstract]
2023 (remaining)	$ 20,920
2024	24,607
2025	17,727
2026	13,952
2027	13,429
Thereafter	46,636
Total Intangible Assets—Net	$ 137,271	$ 142,107

Accounts Payable and Other Ac_3

Accounts Payable and Other Accrued Liabilities - Summary of Accounts Payable and Other Accrued Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Payables and Accruals [Abstract]
Accounts payable	$ 24,399	$ 25,353
Accrued expenses	16,311	14,754
Other business acquisitions purchase price obligations	450	1,185
Contract liabilities	10,932	18,549
Other current liabilities	3,328	3,571
Total accounts payable and other accrued liabilities	$ 55,420	$ 63,412

Accrued Payroll and Benefits -

Accrued Payroll and Benefits - Schedule of Accrued Payroll and Benefits (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Statement of Financial Position [Abstract]
Accrued bonuses	$ 3,559	$ 8,624
Accrued paid time off	1,161	1,088
Accrued payroll	9,084	8,410
Accrued other	2,548	2,406
Total accrued payroll and benefits	$ 16,352	$ 20,528

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Income Tax Disclosure [Abstract]
Annual effective tax rate ("ETR") from continuing operations	10.20%	(20.20%)
Income tax (benefit) expense	$ 1,367,000	$ 1,269,000
Federal statutory rate	21%
Uncertain tax positions	$ 0

Debt - Schedule of Debt (Detail

Debt - Schedule of Debt (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Line Of Credit Facility [Line Items]
Less deferred debt issuance costs	$ (1,595)	$ (1,725)
Total debt	162,467	164,525
Less current portion of long-term debt	(13,125)	(12,031)
Long-term debt, less current portion	149,342	152,494
Term Loan Facility
Line Of Credit Facility [Line Items]
Total debt	$ 164,062	$ 166,250

Debt - Additional Information (

Debt - Additional Information (Details) - USD ($)				1 Months Ended		3 Months Ended		7 Months Ended	12 Months Ended
	Jan. 27, 2022	Jan. 26, 2022	Apr. 27, 2021	Apr. 30, 2023	Jan. 31, 2023	Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2023	Dec. 31, 2022
Floating Component | Interest Rate Swap
Line Of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	$ 100,000,000
Credit facility maturity date	Jan. 27, 2025
Interest rate	1.39%
2021 Credit Facility
Line Of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity			$ 300,000,000
Credit facility maturity date			Apr. 27, 2026
Percentage of interest rate reduction								0.05%
Maximum net leverage ratio			425%
Maximum net leverage ratio year two			400%
Maximum net leverage ratio year three			375%
Minimum fixed charge coverage ratio			125%
Consolidated total leverage ratio						140%			130%
Percentage of proceeds of debt, subject to customary exceptions						100%
Percentage of proceeds of certain dispositions, subject to customary reinvestment rights						100%
Percentage of proceeds of insurance or condemnation, subject to customary reinvestment rights						100%
Weighted average interest rate						6.10%	1.80%	6.10%
Incremental Term Loans
Line Of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity			$ 150,000,000
Equipment Line Of Credit
Line Of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity									$ 10,000,000
Credit facility maturity date						Mar. 31, 2023
Term Loan Facility | 2021 Credit Facility
Line Of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity			175,000,000
Installment repayment amount		$ 2,200,000		$ 2,200,000	$ 2,200,000		$ 2,200,000
Revolving Line of Credit | 2021 Credit Facility
Line Of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity			125,000,000
Revolving Line of Credit | Letter of Credit | 2021 Credit Facility
Line Of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity			$ 20,000,000

Debt - Summary of Term Loan Amo

Debt - Summary of Term Loan Amortization (Details) - 2021 Credit Facility - Term Loan Facility	3 Months Ended
	Mar. 31, 2023
Subsequent Event [Line Items]
Debt instrument, quarterly installment rate, June 30, 2023	1.25%
Debt instrument, quarterly installment rate, September 30, 2023	1.25%
Debt instrument, quarterly installment rate, December 31, 2023	1.88%
Debt instrument, quarterly installment rate, March 31, 2024	1.88%
Debt instrument, quarterly installment rate, June 30, 2024	1.88%
Debt instrument, quarterly installment rate, September 30, 2024	1.88%
Debt instrument, quarterly installment rate, December 31, 2024	1.88%
Debt instrument, quarterly installment rate, March 31, 2025	1.88%
Debt instrument, quarterly installment rate, June 30, 2025	1.88%
Debt instrument, quarterly installment rate, September 30, 2025	1.88%
Debt instrument, quarterly installment rate, December 31, 2025	2.50%
Debt instrument, quarterly installment rate, March 31, 2026	2.50%
Debt instrument, quarterly installment rate, April 27, 2026	Remaining balance

Debt - Summary of 2021 Credit F

Debt - Summary of 2021 Credit Facility Interest Rate Subject to Leverage Ratio and LIBOR (Details) - 2021 Credit Facility	Apr. 27, 2021
Pricing Tier1
Subsequent Event [Line Items]
Commitment Fee	0.25%
Letter of Credit Fee	2.50%
Pricing Tier1 | Minimum
Subsequent Event [Line Items]
Net Leverage Ratio	375%
Pricing Tier1 | LIBOR Plus
Subsequent Event [Line Items]
Interest rate	2.50%
Pricing Tier1 | Base Rate Plus
Subsequent Event [Line Items]
Interest rate	1.50%
Pricing Tier2
Subsequent Event [Line Items]
Commitment Fee	0.23%
Letter of Credit Fee	2.25%
Pricing Tier2 | Maximum
Subsequent Event [Line Items]
Net Leverage Ratio	375%
Pricing Tier2 | Minimum
Subsequent Event [Line Items]
Net Leverage Ratio	325%
Pricing Tier2 | LIBOR Plus
Subsequent Event [Line Items]
Interest rate	2.25%
Pricing Tier2 | Base Rate Plus
Subsequent Event [Line Items]
Interest rate	1.25%
Pricing Tier3
Subsequent Event [Line Items]
Commitment Fee	0.20%
Letter of Credit Fee	2%
Pricing Tier3 | Maximum
Subsequent Event [Line Items]
Net Leverage Ratio	325%
Pricing Tier3 | Minimum
Subsequent Event [Line Items]
Net Leverage Ratio	250%
Pricing Tier3 | LIBOR Plus
Subsequent Event [Line Items]
Interest rate	2%
Pricing Tier3 | Base Rate Plus
Subsequent Event [Line Items]
Interest rate	1%
Pricing Tier4
Subsequent Event [Line Items]
Commitment Fee	0.15%
Letter of Credit Fee	1.75%
Pricing Tier4 | Maximum
Subsequent Event [Line Items]
Net Leverage Ratio	250%
Pricing Tier4 | Minimum
Subsequent Event [Line Items]
Net Leverage Ratio	175%
Pricing Tier4 | LIBOR Plus
Subsequent Event [Line Items]
Interest rate	1.75%
Pricing Tier4 | Base Rate Plus
Subsequent Event [Line Items]
Interest rate	0.75%
Pricing Tier5
Subsequent Event [Line Items]
Commitment Fee	0.15%
Letter of Credit Fee	1.50%
Pricing Tier5 | Maximum
Subsequent Event [Line Items]
Net Leverage Ratio	175%
Pricing Tier5 | LIBOR Plus
Subsequent Event [Line Items]
Interest rate	1.50%
Pricing Tier5 | Base Rate Plus
Subsequent Event [Line Items]
Interest rate	0.50%

Debt - Schedule of Aggregate An

Debt - Schedule of Aggregate Annual Maturities of Long-Term Debt (Details) $ in Thousands	Mar. 31, 2023 USD ($)
Debt Disclosure [Abstract]
2024	$ 13,125
2025	13,125
2026	15,312
2027	122,500
Total	$ 164,062

Fair Value of Financial Instr_3

Fair Value of Financial Instruments - Summary of Financial Instruments Measured at Fair Value on Recurring Basis Using Significant Unobservable Inputs (Level 3) (Details) - Fair Value, Recurring - Level 3 - USD ($) $ in Thousands	Mar. 31, 2023		Dec. 31, 2022		Mar. 31, 2022	Dec. 31, 2021
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Level 3 Liabilities	$ 34,491		$ 33,986		$ 30,632	$ 58,881
Level 3 Assets	5,078		6,046		3,005
Business Acquisitions Contingent Consideration, Current
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Level 3 Liabilities	4,734		3,801		1,429	31,450
Business Acquisitions Contingent Consideration, Long-Term
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Level 3 Liabilities	3,121		4,454		5,566	4,350
Conversion Option
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Level 3 Liabilities	26,636		25,731		23,637	$ 23,081
Interest Rate Swap
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Level 3 Assets	$ 5,078	[1]	$ 6,046	[1]	$ 3,005
[1] Included in other assets in the unaudited condensed consolidated statement of financial position.

Fair Value of Financial Instr_4

Fair Value of Financial Instruments - Summary of Financial Instruments Measured at Fair Value on Recurring Basis (Details) - Fair Value, Recurring - Level 3 - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2023		Mar. 31, 2022
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Beginning balance		$ 33,986		$ 58,881
Total Assets, Beginning balance		6,046
Acquisitions		25		1,216
Changes in fair value included in earnings		507		535
Asset value, Changes in fair value included in earnings		(968)		3,005
Payment of contingent consideration payable		(27)		(30,000)
Ending balance		34,491		30,632
Total Assets, Ending balance		5,078		3,005
Business Acquisitions Contingent Consideration, Current
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Beginning balance		3,801		31,450
Acquisitions		25
Changes in fair value included in earnings		(515)		(21)
Payment of contingent consideration payable		(27)		(30,000)
Reclass of long term to short term contingent liabilities		1,450
Ending balance		4,734		1,429
Business Acquisitions Contingent Consideration, Long-Term
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Beginning balance		4,454		4,350
Acquisitions				1,216
Changes in fair value included in earnings		117
Reclass of long term to short term contingent liabilities		(1,450)
Ending balance		3,121		5,566
Conversion Option
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Beginning balance		25,731		23,081
Changes in fair value included in earnings		905		556
Ending balance		26,636		23,637
Interest Rate Swap
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Assets, Beginning balance	[1]	6,046
Asset value, Changes in fair value included in earnings		(968)		3,005
Total Assets, Ending balance		$ 5,078	[1]	$ 3,005
[1] Included in other assets in the unaudited condensed consolidated statement of financial position.

Convertible and Redeemable Se_2

Convertible and Redeemable Series A-2 Preferred Stock - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended
	Apr. 13, 2020	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Temporary Equity [Line Items]
Period between issuance and expiration of outstanding warrant	10 years
Proceeds from the Series A-2 and Warrant	$ 175,000
Preferred stock, dividends paid		$ 4,100	$ 4,100
Number of debt incurrence test ratio		4.5
Compound embedded derivative, change in net fair value		$ (1,873)	2,449
Convertible And Redeemable Series A-2 Preferred Stock
Temporary Equity [Line Items]
Number of shares issued	17,500	17,500		17,500
Par value per share	$ 0.0001	$ 0.0001		$ 0.0001
Debt issuance costs, net	$ 1,300
Preferred stock, dividends paid		$ 4,100	4,100
Percentage of discount on common stock market price		15%
Percentage of dividend rate steps downs per year		9%
Percentage of dividend rate increase per annum in the event of noncompliance		12%
Number of days dividend increase rate applicable noncompliance event occurred		90 days
Percentage of dividend rate increase per annum upon noncompliance occurred and thereafter		14%
Minimum repayment amount		$ 25,000
Temporary equity description		The Company may, at its option on any one or more dates, redeem all or a minimum portion (the lesser of (i) $25.0 million in aggregate stated value of the Convertible and Redeemable Series A-2 Preferred Stock and (ii) all of the Convertible and Redeemable Series A-2 Preferred Stock then outstanding) of the outstanding Convertible and Redeemable Series A-2 Preferred Stock in cash.With respect to any redemption of any share of the Convertible and Redeemable Series A-2 Preferred Stock prior to the third-year anniversary, the Company is subject to a make whole penalty in which the holders of the Convertible and Redeemable Series A-2 Preferred Stock are guaranteed a minimum repayment equal to outstanding redeemed stated value plus three years of dividends accrued or accruable thereon.
Aggregate stated value of stock redeemed		$ 25,000
Compound embedded derivative, fair value net		26,600		$ 25,700
Convertible And Redeemable Series A-2 Preferred Stock | Other Expense
Temporary Equity [Line Items]
Compound embedded derivative, change in net fair value		900	$ 600
Convertible And Redeemable Series A-2 Preferred Stock | 60-Day Period Prior to Seventh Anniversary
Temporary Equity [Line Items]
Temporary equity convertible into common stock		60,000
Convertible And Redeemable Series A-2 Preferred Stock | Year 5
Temporary Equity [Line Items]
Temporary equity convertible into common stock		60,000
Convertible And Redeemable Series A-2 Preferred Stock | Year 6
Temporary Equity [Line Items]
Temporary equity convertible into common stock		$ 120,000

Stockholder's Equity - Addition

Stockholder's Equity - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended		12 Months Ended
		Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2021	Dec. 31, 2022
Class Of Stock [Line Items]
Common stock, shares authorized		190,000,000			190,000,000
Common stock, par value		$ 0.000004			$ 0.000004
Total unrecognized stock compensation expense related to unvested options, restricted stock and stock appreciation rights granted under the Plans		$ 146.6	$ 173.1
Unrecognized expense expected to be recognized period		4 years
Restricted shares became fully vested and released as common stock		90,116	25,289
Shares, granted	[1]	90,116	25,289
Restricted shares outstanding		2,528,383	2,064,197
Montrose 2017 Stock Incentive Plan
Class Of Stock [Line Items]
Shares, granted		200,423
Restricted shares forfeited		0	0
Montrose 2017 Stock Incentive Plan | Restricted Stock
Class Of Stock [Line Items]
Shares RSAs granted		17,346	10,920
Montrose 2017 Stock Incentive Plan | Stock Options | Board of Directors
Class Of Stock [Line Items]
Shares of vested over period		4 years
Montrose 2017 Stock Incentive Plan | Stock Options | Executive Officers
Class Of Stock [Line Items]
Shares of vested over period		3 years
Vesting frequency of period		1 year
Montrose 2017 Stock Incentive Plan | Stock Options | On the two-year anniversary of the grant | Board of Directors
Class Of Stock [Line Items]
Shares, vesting rights, percentage		50%
Montrose 2017 Stock Incentive Plan | Stock Options | Fourth Anniversary | Board of Directors
Class Of Stock [Line Items]
Shares, vesting rights, percentage		50%
Montrose Amended and Restated 2013 Stock Option Plan
Class Of Stock [Line Items]
Shares outstanding from exercised options		1,434,885	1,239,697
Two Thousand Seventeen Plan | Stock Appreciation Rights (SARs)
Class Of Stock [Line Items]
Shares, granted		3,000,000
Exercise price				$ 66.79
Shares of vested over period				5 years
Remaining contractual terms		10 years
Fair value vested in period		$ 46
Weighted average remaining contract life		8 years 8 months 15 days
Supplemental Incentive Plans
Class Of Stock [Line Items]
Shares, granted		246,417	95,404
Supplemental Incentive Plans | RSUs
Class Of Stock [Line Items]
Shares of vested over period		4 years
Supplemental Incentive Plans | RSUs | First Quater
Class Of Stock [Line Items]
Shares, vesting rights, percentage		33.33%
Supplemental Incentive Plans | RSUs | First Anniversary
Class Of Stock [Line Items]
Shares, vesting rights, percentage		33.33%
Supplemental Incentive Plans | RSUs | Second Anniversary
Class Of Stock [Line Items]
Shares, vesting rights, percentage		33.33%
[1] Represents the non-cash release of common shares due to the vesting of restricted stock.

Stockholder's Equity - Summary

Stockholder's Equity - Summary of Issued Shares of Common Stock (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended
		Mar. 31, 2023	Mar. 31, 2022
Equity [Abstract]
Exercise of options, Shares		124,455	30,607
Restricted shares, net	[1]	90,116	25,289
Total, Shares		214,571	55,896
Exercise of options, Average Price per Share		$ 21.61	$ 14.03
Restricted shares, net, Average Price per Share	[1]	36.81	66.58
Total, Average Price per Share		$ 27.99	$ 37.81
Exercise of options, Total		$ 2,690	$ 429
Total		$ 2,690	$ 429
[1] Represents the non-cash release of common shares due to the vesting of restricted stock.

Stockholder's Equity - Summar_2

Stockholder's Equity - Summary of Number of Shares Authorized to be Issued and Available for Grant (Details) - shares		Mar. 31, 2023		Jan. 31, 2023	Mar. 31, 2022		Jan. 31, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares authorized to be issued		8,366,932			10,177,131
Shares available for grant	[1]	893,522			577,139
2017 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares authorized to be issued		6,329,913			8,272,487
Shares available for grant		893,522	[1]	1,189,801	577,139	[1]	1,185,112
2013 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares authorized to be issued		2,037,019			1,904,644
[1] In January 2023 and January 2022 the Board of Directors ratified the addition of 1,189,801 and 1,185,112 shares of common stock, respectively, to the number of shares available for issuance under the 2017 Plan pursuant to the annual increase provision of such plan. Unless the Board of Directors determines otherwise, additional annual increases will be effective on each January 1, through January 1, 2027. The 2017 Plan permits the company to settle awards, if and when vested, in cash at its discretion. Pursuant to the terms of the 2017 Plan, the number of shares authorized for issuance thereunder will only be reduced with respect to shares of common stock actually issued upon exercise or settlement of an award. Shares of common stock subject to awards that have been canceled, expired, forfeited or otherwise not issued under an award and shares of common stock subject to awards settled in cash do not count as shares of common stock issued under the 2017 Plan. Shares available for grant exclude awards of stock appreciation rights approved in December 2021 that are subject to vesting based on the achievement of certain market conditions, which have not yet been, and may not be, a chieved. See footnote 1 to the table in Common Stock Reserved for Future Issuance below for additional information on stock appreciation rights.

Stockholders' Equity - Summary

Stockholders' Equity - Summary of Number of Shares Authorized to be Issued and Available for Grant (Parenthetical) (Details) - shares		Mar. 31, 2023		Jan. 31, 2023	Mar. 31, 2022		Jan. 31, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares available for grant	[1]	893,522			577,139
2017 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares available for grant		893,522	[1]	1,189,801	577,139	[1]	1,185,112
[1] In January 2023 and January 2022 the Board of Directors ratified the addition of 1,189,801 and 1,185,112 shares of common stock, respectively, to the number of shares available for issuance under the 2017 Plan pursuant to the annual increase provision of such plan. Unless the Board of Directors determines otherwise, additional annual increases will be effective on each January 1, through January 1, 2027. The 2017 Plan permits the company to settle awards, if and when vested, in cash at its discretion. Pursuant to the terms of the 2017 Plan, the number of shares authorized for issuance thereunder will only be reduced with respect to shares of common stock actually issued upon exercise or settlement of an award. Shares of common stock subject to awards that have been canceled, expired, forfeited or otherwise not issued under an award and shares of common stock subject to awards settled in cash do not count as shares of common stock issued under the 2017 Plan. Shares available for grant exclude awards of stock appreciation rights approved in December 2021 that are subject to vesting based on the achievement of certain market conditions, which have not yet been, and may not be, a chieved. See footnote 1 to the table in Common Stock Reserved for Future Issuance below for additional information on stock appreciation rights.

Stockholder's Equity - Schedule

Stockholder's Equity - Schedule of Stock Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock compensation expense	$ 13,035	$ 10,425
2017 Plan | Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock compensation expense	2,073	2,273
2017 Plan | Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock compensation expense	8,697	5,792
2017 Plan | Stock Appreciation Rights (SARs)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock compensation expense	2,265	2,360
Cost of Revenue
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock compensation expense	892	294
Cost of Revenue | 2017 Plan | Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock compensation expense	349	294
Cost of Revenue | 2017 Plan | Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock compensation expense	543
Selling, General and Administrative Expenses
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock compensation expense	12,143	10,131
Selling, General and Administrative Expenses | 2017 Plan | Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock compensation expense	1,724	1,979
Selling, General and Administrative Expenses | 2017 Plan | Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock compensation expense	8,154	5,792
Selling, General and Administrative Expenses | 2017 Plan | Stock Appreciation Rights (SARs)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock compensation expense	$ 2,265	$ 2,360

Stockholder's Equity - Schedu_2

Stockholder's Equity - Schedule of Restricted Stock Activity (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended
		Mar. 31, 2023	Mar. 31, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Average Price per Share	[1]	$ 36.81	$ 66.58
Montrose 2017 Stock Incentive Plan | Restricted stock units awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares		464,186	106,324
Average Price per Share		$ 32.62	$ 46.82
Fair Value		$ 15,140	$ 4,978
[1] Represents the non-cash release of common shares due to the vesting of restricted stock.

Stockholders' Equity - Summar_2

Stockholders' Equity - Summary of Performance Hurdles (Details)	3 Months Ended
	Mar. 31, 2023 $ / shares
SAR Stock Price Performance Hurdle One
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
SARs Stock Price Performance Hurdle	$ 133.58
Portion of SARs Subject to Performance Hurdle	0.33%
SAR Stock Price Performance Hurdle Two
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
SARs Stock Price Performance Hurdle	$ 166.98
Portion of SARs Subject to Performance Hurdle	0.33%
SAR Stock Price Performance Hurdle Three
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
SARs Stock Price Performance Hurdle	$ 200.37
Portion of SARs Subject to Performance Hurdle	0.33%

Stockholder's Equity - Summar_3

Stockholder's Equity - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022	Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options to Purchase Common Stock Exercised	(124,455)	(30,607)
Montrose 2017 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options to Purchase Common Stock Outstanding Beginning Balance	2,579,566	2,036,729	2,036,729
Options to Purchase Common Stock Granted	233,955	547,884
Options to Purchase Common Stock Forfeited/cancelled	(34,619)	(23,082)
Options to Purchase Common Stock Exercised	(101,279)	(11,547)
Options to Purchase Common Stock Outstanding Ending Balance	2,677,623	2,549,984	2,579,566	2,036,729
Options to Purchase Common Stock Exercisable	1,305,511
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted-Average Exercise Price per Share Outstanding Beginning Balance	$ 31	$ 26	$ 26
Weighted-Average Exercise Price per Share Granted	32	44
Weighted-Average Exercise Price per Share Forfeited/cancelled	35	36
Weighted-Average Exercise Price per Share Exercised	25	27
Weighted-Average Exercise Price per Share Outstanding Ending Balance	31	30	31	$ 26
Weighted-Average Exercise Price per Share Exercisable	29
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted Average Grant Date Fair Value per Share Outstanding Beginning Balance	15	14	14
Weighted Average Grant Date Fair Value per Share Granted	14	16
Weighted Average Grant Date Fair Value per Share Ending Balance	$ 15	$ 14	$ 15	$ 14
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted Average Remaining Contract Life (in Years) Outstanding	7 years 9 months 10 days	8 years 5 months 15 days	7 years 9 months 3 days	8 years 3 months 18 days
Weighted Average Remaining Contract Life (in Years) Exercisable	7 years 2 months 8 days
Aggregate Intrinsic Value of In-The-Money Options Outstanding	$ 21,127	$ 59,955	$ 37,292	$ 91,030
Aggregate Intrinsic Value of In-The-Money Options Exercised	2,467	$ 313
Aggregate Intrinsic Value of In-The-Money Options Exercisable	$ 11,880
Montrose Amended and Restated 2013 Stock Option Plan
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options to Purchase Common Stock Outstanding Beginning Balance	855,695	897,674	897,674
Options to Purchase Common Stock Exercised	(23,176)	(19,060)
Options to Purchase Common Stock Outstanding Ending Balance	832,519	878,614	855,695	897,674
Options to Purchase Common Stock Exercisable	832,519
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted-Average Exercise Price per Share Outstanding Beginning Balance	$ 6	$ 6	$ 6
Weighted-Average Exercise Price per Share Exercised	9	6
Weighted-Average Exercise Price per Share Outstanding Ending Balance	6	6	6	$ 6
Weighted-Average Exercise Price per Share Exercisable	6
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted Average Grant Date Fair Value per Share Outstanding Beginning Balance	2	2	2
Weighted Average Grant Date Fair Value per Share Ending Balance	$ 2	$ 2	$ 2	$ 2
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted Average Remaining Contract Life (in Years) Outstanding	3 years 10 days	4 years 1 month 17 days	3 years 3 months 21 days	4 years 4 months 13 days
Weighted Average Remaining Contract Life (in Years) Exercisable	3 years 10 days
Aggregate Intrinsic Value of In-The-Money Options Outstanding	$ 24,393	$ 40,860	$ 32,478	$ 57,529
Aggregate Intrinsic Value of In-The-Money Options Exercised	963	$ 821
Aggregate Intrinsic Value of In-The-Money Options Exercisable	$ 24,393

Stockholder's Equity - Summar_4

Stockholder's Equity - Summary of Weighted Average Assumptions Used in Black-Sholes Option-pricing Model (Details) - $ / shares	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock value (per share)	$ 32.16	$ 44.11
Expected volatility	33.79%	33.45%
Risk-free interest rate	3.72%	1.74%
Expected life (years)	7 years	6 years 3 months 29 days
Forfeiture rate	0%	0%
Dividend rate	0%	0%

Stockholder's Equity - Schedu_3

Stockholder's Equity - Schedule of Common Stock Reserved for Future Issuance (Details) - shares	Mar. 31, 2023		Jan. 31, 2023	Mar. 31, 2022		Jan. 31, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	9,555,449			8,772,532
Montrose 2013 Stock Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	832,519			878,614
Montrose 2017 Stock Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	8,722,930	[1]	1,189,801	7,893,918	[1]	1,185,112
[1] In January 2023 and 2022, the Board of Directors ratified the addition of 1,189,801 and 1,185,112 sha res of common stock, respectively, to the number of shares available for issuance under the 2017 Plan pursuant to the annual increase provision of such plan. Unless the Board of Directors determines otherwise, additional annual increases will be effective on each January 1, through January 1, 2027. The 2017 Plan permits the company to settle awards, if and when vested, in cash at its discretion. Pursuant to the terms of the 2017 Plan, the number of shares authorized for issuance thereunder will only be reduced with respect to shares of common stock actually issued upon exercise or settlement of an award. Shares of common stock subject to awards that have been canceled, expired, forfeited or otherwise not issued under an award and shares of common stock subject to awards settled in cash do not count as shares of common stock issued under the 2017 Plan. The Company expects to have sufficient shares available under the 2017 Plan to satisfy the future settlement of outstanding awards. Shares reserved for future issuance include 3,000,000 shares underlying the 3,000,000 performance SARs granted in December 2021 that are subject to vesting based on the achievement of certain market conditions. Assuming achievement at the highest price performance hurdle, approximately 2,000,000 shares of common stock would be issued upon vesting of these performance SARs. To date, none of the market conditions have been achieved.

Stockholders' Equity - Schedule

Stockholders' Equity - Schedule of Common Stock Reserved for Future Issuance (Parenthetical) (Details) - shares	1 Months Ended
	Jan. 31, 2021	Mar. 31, 2023		Jan. 31, 2023	Mar. 31, 2022		Jan. 31, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance		9,555,449			8,772,532
Montrose 2017 Stock Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance		8,722,930	[1]	1,189,801	7,893,918	[1]	1,185,112
Stock Appreciation Rights Units Grant
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance							3,000,000
Common stock issued upon vesting of performance SARs	2,000,000
[1] In January 2023 and 2022, the Board of Directors ratified the addition of 1,189,801 and 1,185,112 sha res of common stock, respectively, to the number of shares available for issuance under the 2017 Plan pursuant to the annual increase provision of such plan. Unless the Board of Directors determines otherwise, additional annual increases will be effective on each January 1, through January 1, 2027. The 2017 Plan permits the company to settle awards, if and when vested, in cash at its discretion. Pursuant to the terms of the 2017 Plan, the number of shares authorized for issuance thereunder will only be reduced with respect to shares of common stock actually issued upon exercise or settlement of an award. Shares of common stock subject to awards that have been canceled, expired, forfeited or otherwise not issued under an award and shares of common stock subject to awards settled in cash do not count as shares of common stock issued under the 2017 Plan. The Company expects to have sufficient shares available under the 2017 Plan to satisfy the future settlement of outstanding awards. Shares reserved for future issuance include 3,000,000 shares underlying the 3,000,000 performance SARs granted in December 2021 that are subject to vesting based on the achievement of certain market conditions. Assuming achievement at the highest price performance hurdle, approximately 2,000,000 shares of common stock would be issued upon vesting of these performance SARs. To date, none of the market conditions have been achieved.

Net Loss Per Share - Computatio

Net Loss Per Share - Computation of Basic and Diluted Net Loss Per Share Attributable to Common Stockholders (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Earnings Per Share [Abstract]
Net loss	$ (14,719)	$ (7,536)
Convertible and redeemable series A-2 preferred stock dividend	(4,100)	(4,100)
Net loss attributable to common stockholders -basic and diluted	$ (18,819)	$ (11,636)
Weighted-average common shares outstanding - basic	29,857	29,662
Weighted-average common shares outstanding - diluted	29,857	29,662
Net loss per share attributable to common stockholders - basic	$ (0.63)	$ (0.39)
Net loss per share attributable to common stockholders - diluted	$ (0.63)	$ (0.39)

Net Loss Per Share - Common Sto

Net Loss Per Share - Common Stock Equivalents Excluded from Calculation of Diluted Loss Per Share Attributable to Common Stockholders (Details) - shares		3 Months Ended
		Mar. 31, 2023	Mar. 31, 2022
Stock Options
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of loss per share amount	[1]	3,510,142	2,034,041
Restricted Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of loss per share amount	[1]	2,151,785	1,777,958
Series A-2
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of loss per share amount	[1]	4,735,220	4,329,640
Stock Appreciation Rights (SARs)
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of loss per share amount	[1]	3,000,000	3,000,000
[1] Includes 7,362,459 and 5,008,269 common stock equivalents that are out of the money as of March 31, 2023 and March 31, 2022 , respectively.

Net Loss Per Share - Common S_2

Net Loss Per Share - Common Stock Equivalents Excluded from Calculation of Diluted Net Loss per Share Attributable to Common Stockholders (Parenthetical) (Details) - shares	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Earnings Per Share [Abstract]
Number of shares out of money	7,362,459	5,008,269

Segment Information - Additiona

Segment Information - Additional Information (Details)	3 Months Ended
	Mar. 31, 2023 Segment
Segment Reporting [Abstract]
Number of operating segments	3
Number of reportable segments	3

Segment Information - Component

Segment Information - Components of Segment Revenues and Adjusted EBITDA (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2023	Mar. 31, 2022
Segment Reporting Information [Line Items]
Segment Revenues		$ 131,428	$ 134,680
Segment Adjusted EBITDA		16,603	16,451	[1]
Operating Segments
Segment Reporting Information [Line Items]
Segment Revenues		131,428	134,680
Segment Adjusted EBITDA		25,931	23,938	[1]
Assessment, Permitting and Response | Operating Segments
Segment Reporting Information [Line Items]
Segment Revenues		52,214	45,600
Segment Adjusted EBITDA		14,266	9,623	[1]
Measurement and Analysis | Operating Segments
Segment Reporting Information [Line Items]
Segment Revenues	[2]	42,527	39,761
Segment Adjusted EBITDA		6,387	6,322	[1],[3]
Remediation and Reuse | Operating Segments
Segment Reporting Information [Line Items]
Segment Revenues		36,687	49,319
Segment Adjusted EBITDA		5,278	7,993	[1]
Corporate and Other
Segment Reporting Information [Line Items]
Segment Adjusted EBITDA		$ (9,328)	$ (7,487)	[1]
[1] Includes the add back of start-up losses and investment in new services of $ 0.8 million. Includes revenue of $ 1.4 million and $ 5.6 million from the Discontinuing Specialty Lab, for the three months ended March 31, 2023 and March 31, 2022, respectively. Includes Adjusted EBITDA of $ 1.3 million from the Discontinuing Specialty Lab.

Segment Information - Compone_2

Segment Information - Components of Segment Revenues and Adjusted EBITDA (Parenthetical) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Segment Reporting Information [Line Items]
Segment Revenues	$ 131,428	$ 134,680
Segment Adjusted EBITDA	16,603	16,451	[1]
Discontinuing Specialty Lab
Segment Reporting Information [Line Items]
Segment Revenues	$ 1,400	5,600
Segment Adjusted EBITDA		1,300
Start-up Losses and Investment in New Services
Segment Reporting Information [Line Items]
Segment Adjusted EBITDA		$ 800
[1] Includes the add back of start-up losses and investment in new services of $ 0.8 million.

Segment Information - Reconcili

Segment Information - Reconciliation of Segment Measure to Net Loss (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2023	Mar. 31, 2022
Segment Reporting Information [Line Items]
Total		$ 16,603	$ 16,451	[1]
Interest expense, net		(1,541)	(1,092)
Income tax expense		(1,367)	(1,269)
Depreciation and amortization		(10,555)	(12,144)
Stock-based compensation		(13,035)	(10,425)
Start-up losses and investment in new services			(786)
Acquisition costs		(775)	(467)
Fair value changes in financial instruments		(1,873)	2,449
Fair value changes in business acquisition contingencies		398	21
Expenses related to financing transactions		(4)	(7)
Other losses or expenses		(134)	(267)
Net loss		(14,719)	(7,536)
Discontinuing Specialty Lab
Segment Reporting Information [Line Items]
Total			$ 1,300
Other losses or expenses	[2]	$ 2,436
[1] Includes the add back of start-up losses and investment in new services of $ 0.8 million. Amounts consist of operating losses before depreciation related to the Discontinuing Specialty Lab .

Related-Party Transactions - Ad

Related-Party Transactions - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Related Party Transactions [Abstract]
Related party transaction amount	$ 0	$ 0

Defined Contribution Plan - Add

Defined Contribution Plan - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan, description	401(k) Savings Plan
Defined contribution plan, maximum annual contributions per employee, percent	85%		85%
Defined contribution plan, employer matching contribution, percent of match	100%
Defined contribution plan participant's compensation percent	3%
Defined contribution plan percentage of participant's elective deferrals	50%
Selling, General and Administrative Expenses
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan, employer discretionary contribution amount	$ 2.1	$ 1.7
Minimum
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan participant's compensation percent	3%
Maximum
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan participant's compensation percent	5%

Subsequent Events - Additional

Subsequent Events - Additional Information (Details) - Subsequent Event	May 01, 2023	Apr. 28, 2023
GreenPath
Subsequent Event [Line Items]
Percentage of interests acquired	100%
Matrix
Subsequent Event [Line Items]
Percentage of interests acquired		100%

Subsequent Events - Schedule of

Subsequent Events - Schedule of Main Elements of Purchase Price of Acquisitions (Details) $ in Thousands, $ in Thousands				3 Months Ended
		May 01, 2023 CAD ($)	Apr. 28, 2023 CAD ($)	Mar. 31, 2023 USD ($)
Subsequent Event [Line Items]
Cash				$ 6,536
Total Purchase Price				$ 6,219
Subsequent Event | GreenPath
Subsequent Event [Line Items]
Cash	[1]	$ 16,580
Common Stock		3,520
Total Purchase Price		$ 20,100
Subsequent Event | Matrix
Subsequent Event [Line Items]
Cash	[2]		$ 65,191
Total Purchase Price			$ 65,191
[1] The cash portion of this acquisition's purchase price was funded through cash on hand. Upon closing, the cash portion of this acquisition's purchase price will funded through a combination of cash on hand and proceeds received from our revolving credit facility.