Montrose Environmental (MEG) 10-Q 7 Aug 24 2024 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2024	Aug. 02, 2024
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2024
Document Quarterly Report	true
Document Transition Report	false
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q2
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		34,229,939
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	Jun. 30, 2024	Dec. 31, 2023
Current assets:
Cash, cash equivalents and restricted cash	$ 16,905	$ 23,240
Accounts receivable, net	135,669	112,360
Contract assets	73,224	51,629
Prepaid and other current assets	14,222	13,695
Total current assets	240,020	200,924
Non-current assets:
Property and equipment, net	63,627	56,825
Operating lease right-of-use asset, net	38,898	32,260
Finance lease right-of-use asset, net	14,827	13,248
Goodwill	435,483	364,449
Other intangible assets, net	142,870	140,813
Other assets	8,191	8,267
Total assets	943,916	816,786
Current liabilities:
Accounts payable and other accrued liabilities	58,223	59,920
Accrued payroll and benefits	28,339	34,660
Business acquisitions contingent consideration, current	6,351	3,592
Current portion of operating lease liabilities	11,134	9,963
Current portion of finance lease liabilities	4,005	3,956
Current portion of long-term debt	23,667	14,196
Total current liabilities	131,719	126,287
Non-current liabilities:
Business acquisitions contingent consideration, long-term	9,595	2,448
Other non-current liabilities	6,118	6,569
Deferred tax liabilities, net	8,238	6,064
Operating lease liability, net of current portion	30,003	25,048
Finance lease liability, net of current portion	8,223	8,185
Long-term debt, net of deferred financing fees	188,749	148,988
Total liabilities	402,215	342,606
Commitments and contingencies
Stockholders' equity:
Additional paid-in-capital	682,879	531,831
Accumulated deficit	(233,883)	(210,356)
Accumulated other comprehensive (loss) income	(223)	(223)
Total stockholders’ equity	448,773	321,252
Total liabilities, convertible and redeemable series A-2 preferred stock and stockholders' equity	943,916	816,786
Conversion Option
Non-current liabilities:
Conversion option	19,570	19,017
Convertible And Redeemable Series A-2 Preferred Stock
Non-current liabilities:
Redeemable series preferred stock	$ 92,928	$ 152,928

UNAUDITED CONDENSED CONSOLIDA_2

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF FINANCIAL POSITION (Parenthetical) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Common stock, par value	$ 0.000004	$ 0.000004
Common stock, shares authorized	190,000,000	190,000,000
Common stock, shares issued	34,168,713	30,190,231
Common stock, shares outstanding	34,168,713	30,190,231
Convertible And Redeemable Series A-2 Preferred Stock
Temporary equity, par value	$ 0.0001	$ 0.0001
Temporary equity, shares authorized	11,667	17,500
Temporary equity, shares issued	11,667	17,500
Temporary equity, shares outstanding	11,667	17,500
Temporary equity, aggregate liquidation preference	$ 122.2	$ 182.2

UNAUDITED CONDENSED CONSOLIDA_3

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Income Statement [Abstract]
Revenues	$ 173,325	$ 159,101	$ 328,650	$ 290,529
Cost of revenues (exclusive of depreciation and amortization shown below)	104,086	98,196	200,643	179,829
Selling, general and administrative expense	59,239	55,247	116,313	104,860
Fair value changes in business acquisition contingencies	136	353	242	(45)
Depreciation and amortization	12,515	11,398	24,168	21,953
Loss from operations	(2,651)	(6,093)	(12,716)	(16,068)
Other income (expense), net	(924)	947	(417)	(889)
Interest expense, net	(3,976)	(1,877)	(7,282)	(3,418)
Total other income (expense), net	(4,900)	(930)	(7,699)	(4,307)
Loss before expense from income taxes	(7,551)	(7,023)	(20,415)	(20,375)
Income tax expense	2,619	151	3,112	1,518
Net loss	(10,170)	(7,174)	(23,527)	(21,893)
Equity adjustment from foreign currency translation	35	(118)		(106)
Comprehensive loss	(10,135)	(7,292)	(23,527)	(21,999)
Convertible and redeemable series A-2 preferred stock dividend	(2,750)	(4,100)	(5,564)	(8,200)
Net loss attributable to common stockholders	$ (12,920)	$ (11,274)	$ (29,091)	$ (30,093)
Weighted average common shares outstanding - basic	33,318	30,047	31,850	29,952
Weighted average common shares outstanding - diluted	33,318	30,047	31,850	29,952
Net loss per share attributable to common stockholders - basic	$ (0.39)	$ (0.38)	$ (0.91)	$ (1)
Net loss per share attributable to common stockholders - diluted	$ (0.39)	$ (0.38)	$ (0.91)	$ (1)

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 (Loss)
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 stockholders	(4,100)			(4,100)
Common stock issuances pursuant to exercises and vesting of equity awards	2,690			2,690
Common stock issuances pursuant to exercises and vesting of equity awards, shares			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
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	(21,893)
Dividend payment to the Series A-2 preferred stockholders		$ (8,200)
Ending balance at Jun. 30, 2023	313,006			514,494	(201,390)	(98)
Ending balance, shares at Jun. 30, 2023		17,500
Ending balance at Jun. 30, 2023		$ 152,928
Ending balance, shares at Jun. 30, 2023			30,091,479
Beginning balance at Mar. 31, 2023	310,105			504,301	(194,216)	20
Beginning balance, shares at Mar. 31, 2023			29,961,364
Beginning balance at Mar. 31, 2023		$ 152,928
Beginning balance, shares at Mar. 31, 2023		17,500
Net loss	(7,174)				(7,174)
Stock-based compensation	11,090			11,090
Dividend payment to the Series A-2 preferred stockholders	(4,100)	$ (4,100)		(4,100)
Common stock issuances pursuant to exercises and vesting of equity awards	605			605
Common stock issuances pursuant to exercises and vesting of equity awards, shares			43,538
Issuance of common stock pursuant to follow-on offering, shares			130,115
Acquisitions consideration paid in common stock	2,598			2,598
Acquisitions consideration paid in common stock, Shares			86,577
Accumulated other comprehensive income	(118)					(118)
Ending balance at Jun. 30, 2023	313,006			514,494	(201,390)	(98)
Ending balance, shares at Jun. 30, 2023		17,500
Ending balance at Jun. 30, 2023		$ 152,928
Ending balance, shares at Jun. 30, 2023			30,091,479
Beginning balance at Dec. 31, 2023	321,252			531,831	(210,356)	(223)
Beginning balance, shares at Dec. 31, 2023			30,190,231
Beginning balance at Dec. 31, 2023		$ 152,928
Beginning balance, shares at Dec. 31, 2023		17,500
Net loss	(13,357)				(13,357)
Stock-based compensation	11,272			11,272
Redemption of Series A-2 preferred stock		$ (60,000)
Redemption of Series A-2 preferred stock, shares		(5,833)
Dividend payment to the Series A-2 preferred stockholders	(2,814)			(2,814)
Common stock issuances pursuant to exercises and vesting of equity awards	487			487
Common stock issuances pursuant to exercises and vesting of equity awards, shares			171,647
Issuance of common stock pursuant to follow-on offering, shares			427,631
Acquisitions consideration paid in common stock	6,580			6,580
Acquisitions consideration paid in common stock, Shares			220,734
Payment of earn-out liability	1,087			1,087
Payment of earn-out liability, Shares			35,250
Accumulated other comprehensive income	(35)					(35)
Ending balance at Mar. 31, 2024	324,472			548,443	(223,713)	(258)
Ending balance, shares at Mar. 31, 2024		11,667
Ending balance at Mar. 31, 2024		$ 92,928
Ending balance, shares at Mar. 31, 2024			30,617,862
Beginning balance at Dec. 31, 2023	321,252			531,831	(210,356)	(223)
Beginning balance, shares at Dec. 31, 2023			30,190,231
Beginning balance at Dec. 31, 2023		$ 152,928
Beginning balance, shares at Dec. 31, 2023		17,500
Net loss	(23,527)
Dividend payment to the Series A-2 preferred stockholders		$ (5,600)
Ending balance at Jun. 30, 2024	448,773			682,879	(233,883)	(223)
Ending balance, shares at Jun. 30, 2024		11,667
Ending balance at Jun. 30, 2024		$ 92,928
Ending balance, shares at Jun. 30, 2024			34,168,713
Beginning balance at Mar. 31, 2024	324,472			548,443	(223,713)	(258)
Beginning balance, shares at Mar. 31, 2024			30,617,862
Beginning balance at Mar. 31, 2024		$ 92,928
Beginning balance, shares at Mar. 31, 2024		11,667
Net loss	(10,170)				(10,170)
Stock-based compensation	11,831			11,831
Dividend payment to the Series A-2 preferred stockholders	(2,750)	$ (2,800)		(2,750)
Common stock issuances pursuant to exercises and vesting of equity awards	888			888
Common stock issuances pursuant to exercises and vesting of equity awards, shares			39,144
Issuance of common stock pursuant to follow-on offering	121,776			121,776
Issuance of common stock pursuant to follow-on offering, shares			3,450,000
Acquisitions consideration paid in common stock	2,691			2,691
Acquisitions consideration paid in common stock, Shares			61,707
Accumulated other comprehensive income	35					35
Ending balance at Jun. 30, 2024	$ 448,773			$ 682,879	$ (233,883)	$ (223)
Ending balance, shares at Jun. 30, 2024		11,667
Ending balance at Jun. 30, 2024		$ 92,928
Ending balance, shares at Jun. 30, 2024			34,168,713

UNAUDITED CONDENSED CONSOLIDA_5

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023
Operating activities:
Net loss	$ (23,527)	$ (21,893)
Adjustments to reconcile net loss to net cash provided by operating activities:
Depreciation and amortization	24,168	21,953
Amortization of right-of-use asset	5,429	5,041
Stock-based compensation expense	23,103	24,125
Other operating activities, net	4,121	5,439
Changes in operating assets and liabilities,net of acquisitions:
Accounts receivable and contract assets	(38,021)	2,078
Accounts payable and other accrued liabilities	(938)	(5,553)
Accrued payroll and benefits	(7,940)	411
Payment of contingent consideration		(611)
Change in operating leases	(6,306)	(4,805)
Other assets	(1,216)	(1,673)
Net cash (used in) provided by operating activities	(21,127)	24,512
Investing activities:
Proceeds from corporate owned and property insurance	120	86
Purchases of property and equipment	(17,928)	(20,951)
Proceeds from the sale of property and equipment	2,069	0
Proprietary software development and other software costs	(1,736)	(2,041)
Purchase price true ups		(1,027)
Minority investments	(210)
Cash paid for acquisitions, net of cash acquired	(70,252)	(63,050)
Net cash used in investing activities	(87,937)	(86,983)
Financing activities:
Proceeds from line of credit	202,771
Repayment of the line of credit	(199,119)
Proceeds from the aircraft loan		10,935
Repayment of aircraft loan	(526)	0
Proceeds from term loan	50,000
Repayment of term loan	(3,906)	(6,597)
Payment of contingent consideration and other purchase price true ups	(525)	(1,194)
Repayment of finance leases	(3,105)	(2,198)
Payments of deferred financing costs	(348)
Proceeds from issuance of common stock for exercised stock options	1,375	3,295
Proceeds from issuance of common stock in follow-on offering	121,776
Dividend payment to the series A-2 stockholders	(5,564)	(8,200)
Repayment to the series A-2 stockholders	(60,000)
Net cash provided by (used in) financing activities	102,829	(3,959)
Change in cash, cash equivalents and restricted cash	(6,235)	(66,430)
Foreign exchange impact on cash balance	(100)	(91)
Cash, cash equivalents and restricted cash:
Beginning of year	23,240	89,828
End of period	16,905	23,307
Supplemental disclosures of cash flows information:
Cash paid for interest	6,858	2,937
Cash paid for income tax	699	1,261
Supplemental disclosures of non-cash investing and financing activities:
Accrued purchases of property and equipment	1,217	2,304
Property and equipment purchased under finance leases	3,243	3,326
Common stock issued to acquire new businesses	9,271	2,598
Acquisitions unpaid contingent consideration	15,946	$ 6,430
Acquisitions contingent consideration paid in common stock	$ 1,087

Pay vs Performance Disclosure

Pay vs Performance Disclosure - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2024	Mar. 31, 2024	Jun. 30, 2023	Mar. 31, 2023	Jun. 30, 2024	Jun. 30, 2023
Pay vs Performance Disclosure
Net Income (Loss)	$ (10,170)	$ (13,357)	$ (7,174)	$ (14,719)	$ (23,527)	$ (21,893)

Insider Trading Arrangements

Insider Trading Arrangements	6 Months Ended
	Jun. 30, 2024 shares
Trading Arrangements, by Individual
Material Terms of Trading Arrangement	On May 14, 2024 , Allan Dicks , Chief Financial Officer , adopted a trading plan intended to satisfy Rule 10b5-1(c) to (a) sell up to 2,000 shares of Company common stock between November 11, 2024 and November 13, 2025, subject to certain conditions, (b) sell up to 16,310 shares of Company common stock between August 14, 2024 and November 13, 2025, subject to certain conditions, and (c) purchase up to 98,260 shares of Company common stock in connection with the exercise of stock options, and sell up to 98,260 of such shares between August 14, 2024 and November 13, 2025, subject to certain conditions. On May 15, 2024 , Nasym Afsari , General Counsel and Secretary , adopted a trading plan intended to satisfy Rule 10b5-1(c) to (a) sell up to 16,750 shares of Company common stock between August 14, 2024 and February 25, 2025, subject to certain conditions and (b) purchase up to 23,277 shares of Company common stock in connection with the exercise of stock options, and sell up to 23,277 of such shares between August 14, 2024 and February 25, 2025, subject to certain conditions. On June 14, 2024 , James K. Price , Director , adopted a trading plan intended to satisfy Rule 10b5-1(c) to sell 280,000 shares of Company Common Stock between September 12, 2024 and June 13, 2025, subject to certain conditions.
Allan Dicks
Trading Arrangements, by Individual
Name	Allan Dicks
Title	Chief Financial Officer
Rule 10b5-1 Arrangement Adopted	true
Adoption Date	May 14, 2024
Nasym Afsari
Trading Arrangements, by Individual
Name	Nasym Afsari
Title	General Counsel and Secretary
Rule 10b5-1 Arrangement Adopted	true
Adoption Date	May 15, 2024
James K. Price
Trading Arrangements, by Individual
Name	James K. Price
Title	Director
Rule 10b5-1 Arrangement Adopted	true
Adoption Date	June 14, 2024
Rule 10b5-1 Trading Plan Sale of Common Stock between November 11, 2024 and November 13, 2025 | Allan Dicks
Trading Arrangements, by Individual
Aggregate Available	2,000
Rule 10b5-1 Trading Plan Sale of Common Stock between August 14, 2024 and November 13, 2025 | Allan Dicks
Trading Arrangements, by Individual
Aggregate Available	16,310
Rule 10b5-1 Trading Plan Purchase of Common Stock with Exercise of Stock Options between August 14, 2024 and November 13, 2025 | Allan Dicks
Trading Arrangements, by Individual
Aggregate Available	98,260
Rule 10b5-1 Trading Plan Sale of Common Stock between August 14, 2024 and November 13, 2025 | Allan Dicks
Trading Arrangements, by Individual
Aggregate Available	98,260
Rule 10b5-1 Trading Plan Purchase of Common Stock with Exercise of Stock Options between August 14, 2024 and February 25, 2025 | Nasym Afsari
Trading Arrangements, by Individual
Aggregate Available	23,277
Rule 10b5-1 Trading Plan Sale of Common Stock between August 14, 2024 and February 25, 2025 | Nasym Afsari
Trading Arrangements, by Individual
Aggregate Available	16,750
Rule 10b5-1 Trading Plan Sale of Common Stock between August 14, 2024 and February 25, 2025 | Nasym Afsari
Trading Arrangements, by Individual
Aggregate Available	23,277
Rule 10b5-1 Trading Plan Sale of Common Stock between September 12, 2024 and June 13, 2025 | James K. Price
Trading Arrangements, by Individual
Aggregate Available	280,000

Description of the Business and

Description of the Business and Basis of Presentation	6 Months Ended
	Jun. 30, 2024
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 110 offices across the United States, Canada, Australia and Europe and approximately 3,380 employees as of June 30, 2024. 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 segment provides scientific advisory and consulting services to support environmental assessments, environmental emergency response and recovery, toxicology consulting and environmental audits and permits for current operations, facility upgrades, new projects, decommissioning projects and development projects. The Company works closely with clients to navigate the regulatory process at the local, state, provincial and federal levels, identify the potential environmental and political impacts of their decisions and develop practical mitigation approaches, as needed. In addition to environmental toxicology, and given the Company's expertise in helping businesses plan for and respond to disruptions, the Company's scientists and response teams have helped clients navigate their preparation for and response to emergency response situations. Measurement and Analysis segment is one of the largest providers of environmental testing and laboratory services in North America. The Company's highly credentialed 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. The Company's offerings include source and ambient air testing and monitoring, leak detection, and advanced multi-media laboratory services, including air, soil, stormwater, wastewater and drinking water analysis. Remediation and Reuse segment provides clients with engineering, design, and implementation services, primarily to treat contaminated water, remove contaminants from soil or create biogas from waste. The Company's team, including engineers, scientists and consultants, provides these services to assist clients in designing solutions, managing products and mitigating environmental risks and liabilities at their locations. The Company does not own the properties or facilities at which it implements these projects or the underlying liabilities, nor does the Company own material amounts of the equipment used in projects. 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, 2023. 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. Within the unaudited condensed consolidated financial statements certain amounts in the prior period have been reclassified to conform with current period presentation. The Company reclassified $ 1.8 million of provision for bad debt, $ 0.9 million of fair value changes, $ 1.5 million of deferred income taxes, and $ 1.1 million of other activities to other operating activities, net, in the condensed consolidated statements of cash flows for the six months ended June 30, 2023. The Company disaggregated 130,115 shares or $ 3.2 million of common stock issued for quarter ended June 30, 2023, and 427,631 shares or $ 8.2 million of common stock issued for quarter ended March 31, 2024 to separate line items on the condensed consolidated statements of convertible and redeemable series A-2 preferred stock and stockholders’ equity. These changes had no effect on the Company's results of operations or financial position.

Summary of New Accounting Prono

Summary of New Accounting Pronouncements	6 Months Ended
	Jun. 30, 2024
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 November 2023, the Financial Accounting Standards Board ("FASB") issued Accounting Standard Update ("ASU") 2023-07, Improvements to Reportable Segment Disclosures. The amendments improve reportable segment disclosure requirements, primarily through enhanced disclosures about significant segment expenses. In addition, the amendments enhance interim disclosure requirements, clarify circumstances in which an entity can disclose multiple segment measures of profit or loss, provide new segment disclosure requirements for entities with a single reportable segment, and contain other disclosure requirements. The purpose of the amendments is to enable investors to better understand an entity’s overall performance and assess potential future cash flows. ASU 2023-07 is effective for the Company's fiscal year beginning January 1, 2024 and requires the use of a retrospective approach to all prior periods presented. The Company adopted the standard on January 1, 2024 , and plans to adopt the standard for interim periods beginning January 1, 2025. The Company is evaluating the potential impact of its adoption of ASU 2023-07 on the Company's audited Consolidated Financial Statements but does not anticipate that such an adoption will have a material impact. Recently Issued Accounting Pronouncements Not Yet Adopted In August 2023, the FASB issued ASU 2023-05, under which an entity that qualifies as either a joint venture or a corporate joint venture is required to apply a new basis of accounting upon the formation of the joint venture. Specifically, the ASU provides that a joint venture or a corporate joint venture must initially measure its assets and liabilities at fair value on the formation date. The amendments in ASU 2023-05 are effective for all joint ventures within the ASU’s scope that are formed on or after January 1, 2025. Early adoption is permitted. The Company is currently evaluating the impact of the adoption of the standard on its consolidated financial statements. In December 2023, the FASB issued ASU 2023-09, Improvements to Income Tax Disclosures, which improves the transparency of income tax disclosures by requiring consistent categories and greater disaggregation of information in the rate reconciliation and income taxes paid disaggregated by jurisdiction. It also includes certain other amendments to improve the effectiveness of income tax disclosures. ASU 2023-09 is effective for the Company beginning January 1, 2025 and allows the use of a prospective or retrospective approach. The Company is currently evaluating the impact of the adoption of the standard on its consolidated financial statements.

Revenues and Accounts Receivabl

Revenues and Accounts Receivable	6 Months Ended
	Jun. 30, 2024
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 19. 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: June 30, December 31, 2024 2023 Contract assets $ 73,224 $ 51,629 Contract liabilities 13,284 8,132 Contract assets acquired through business acquisitions amounted to $ 2.4 million and $ 2.2 million as of June 30, 2024 and December 31, 2023 , respectively. No material contract liabilities were acquired through business acquisitions as of June 30, 2024 and December 31, 2023. Revenue recognized during the three and six months ended June 30, 2024, included in the contract liabilities balance at the beginning of the year was $ 4.8 million and $ 9.3 million, respectively. The revenue recognized from the contract liabilities consisted of the Company satisfying performance obligations during the normal course of business. Remaining Unsatisfied Performance Obligations —Remaining unsatisfied performance obligations represent the total dollar value of work to be performed on fixed fee contracts awarded primarily within our soil remediation, water treatment, and renewable business lines. 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 June 30, 2024 and December 31, 2023, the estimated revenue expected to be recognized in the future related to performance obligations that are unsatisfied was approximately $ 80.5 million and $ 81.9 million, respectively. As of June 30, 2024, the Company expected to recognize approximately $ 60.5 million of this amount as revenue within a year and $ 20.0 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: June 30, 2024 December 31, 2023 Accounts receivable, invoiced $ 136,972 $ 115,064 Accounts receivable, other 1,481 20 Allowance for doubtful accounts ( 2,784 ) ( 2,724 ) Accounts receivable, net $ 135,669 $ 112,360 The Company had one and zero customer that exceeded 10.0 % of its gross receivables as of June 30, 2024 and December 31, 2023, respectively. For the three and six months ended June 30, 2024, the Company had no customer who accounted for more than 10 % of revenue. During the three and six months ended June 30, 2023 , the Company had one customer who accounted for 12.3 % and 10.4 % of revenue, respectively. 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 Six months ended June 30, 2024 $ 2,724 $ ( 659 ) $ ( 11 ) $ 730 $ 2,784 Year ended December 31, 2023 1,915 3,142 ( 2,333 ) — 2,724 ____________________ (1) This amount consists of additions to the allowance due to business acquisitions.

Prepaid and Other Current Asset

Prepaid and Other Current Assets	6 Months Ended
	Jun. 30, 2024
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: June 30, 2024 December 31, 2023 Deposits $ 1,412 $ 1,764 Prepaid expenses 9,831 8,112 Supplies 2,979 3,819 Prepaid and other current assets $ 14,222 $ 13,695

Property and Equipment, Net

Property and Equipment, Net	6 Months Ended
	Jun. 30, 2024
Property, Plant and Equipment [Abstract]
Property and Equipment, Net	5. PROPERTY AND EQUIPMENT, NET Property and equipment, net, consisted of the following: June 30, 2024 December 31, 2023 Lab and test equipment $ 20,989 $ 20,341 Vehicles 6,096 6,033 Equipment 54,782 50,387 Furniture and fixtures 3,001 2,963 Leasehold improvements 12,444 10,808 Aircraft 12,386 12,312 Building 5,748 5,748 115,446 108,592 Land 1,089 1,089 Construction in progress 10,497 3,956 Less: Accumulated depreciation ( 63,405 ) ( 56,812 ) Total property and equipment—net $ 63,627 $ 56,825 Total depreciation expense included in the unaudited condensed consolidated statements of operations was $ 4.1 million and $ 7.0 million for the three and six months ended June 30, 2024, respectively, and $ 2.6 million and $ 4.8 million for the three and six months ended June 30, 2023 , respectively.

Leases

Leases	6 Months Ended
	Jun. 30, 2024
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, and 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 ("ROU") 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 ROU 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. When a lease is terminated before the expiration of the lease term, irrespective of whether the lease is classified as a finance lease or an operating lease, the lessee would derecognize the ROU asset and corresponding lease liability. Any difference would be recognized as a gain or loss related to the termination of the lease. Similarly, if a lessee is required to make any payments or receives any consideration when terminating the lease, it would include such amounts in the determination of the gain or loss upon termination. The components of lease expense were as follows: For the Three Months Ended June 30, Statement of Operations Location 2024 2023 Operating lease cost Lease cost Selling, general and administrative expense $ 2,956 $ 2,804 Variable lease cost Selling, general and administrative expense 580 299 Total operating lease cost $ 3,536 $ 3,103 Finance lease cost Amortization of right of use assets Depreciation and amortization $ 1,293 $ 1,429 Interest on lease liabilities Interest expense, net 204 171 Total finance lease cost $ 1,497 $ 1,600 Total lease cost $ 5,033 $ 4,703 For the Six Months Ended June 30, Statement of Operations Location 2024 2023 Operating lease cost Lease cost Selling, general and administrative expense $ 5,950 $ 5,545 Variable lease cost Selling, general and administrative expense 1,036 625 Total operating lease cost $ 6,986 $ 6,170 Finance lease cost Amortization of right of use assets Depreciation and amortization $ 2,571 $ 2,583 Interest on lease liabilities Interest expense, net 399 301 Total finance lease cost $ 2,970 $ 2,884 Total lease cost $ 9,956 $ 9,054 Supplemental cash flows information related to leases was as follows: For the Six Months Ended June 30, 2024 2023 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows used in operating leases $ 6,170 $ 5,306 Operating cash flows used in finance leases 399 301 Financing cash flows used in finance leases 3,103 2,198 Lease liabilities arising from new ROU assets: Operating leases 9,694 23,831 Finance leases 2,666 3,326 Weighted average remaining lease terms and weighted average discount rates were: June 30, 2024 Operating Leases Finance Leases Weighted average remaining lease term (years) 4.4 3.4 Weighted average discount rate 4.4 % 6.5 % June 30, 2023 Operating Leases Finance Leases Weighted average remaining lease term (years) 5.5 3.3 Weighted average discount rate 2.8 % 5.8 % 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 2024 $ 6,623 $ 2,547 2025 11,643 4,072 2026 9,342 3,409 2027 6,484 2,408 2028 5,029 1,244 2029 and thereafter 6,362 — Total undiscounted future minimum lease payments $ 45,483 $ 13,680 Less imputed interest ( 4,347 ) ( 1,452 ) Total discounted future minimum lease payments $ 41,136 $ 12,228

Business Acquisitions

Business Acquisitions	6 Months Ended
	Jun. 30, 2024
Business Combinations [Abstract]
Business Acquisitions	7. BUSINESS ACQUISITIONS In line with the Company’s strategic growth initiatives, the Company acquired certain businesses during the six months ended June 30, 2024 and during the year ended December 31, 2023. The results of each of those acquired businesses are included in the unaudited condensed consolidated financial statements beginning on the respective acquisition date. Each transaction qualified as an acquisition of a business and was accounted for as a business combination. The Company may be required to make up to $ 40.4 million in aggregate earn-out payments between the years 2024 and 2026 in connection with certain of its business acquisitions, of which up to $ 14.2 million may be paid only in cash, up to $ 13.1 million may be paid only in common stock and up to $ 13.1 million may be paid, at the Company’s option, in cash or common stock. Transaction costs related to business combinations totaled $ 1.1 million and $ 3.6 million for the three and six months ended June 30, 2024, respectively, and $ 2.7 million and $ 3.5 million for the three and six months ended June 30, 2023, respectively. These costs are expensed within selling, general and administrative expense in the accompanying unaudited condensed consolidated statements of operations. Acquisitions Completed During the Six Months Ended June 30, 2024 Epic Environmental Pty LTD (“EPIC”) —In January 2024, the Company completed the acquisition of EPIC by acquiring 100 % of its common stock. EPIC is an environmental science and engineering consultancy, based in Brisbane, Australia, and serving clients across Australia. Two Dot Consulting, LLC (“2DOT”) —In February 2024, the Company completed the acquisition of 2DOT by acquiring 100 % of its ownership interest. 2DOT is a leading environmental consultancy specializing in regulatory services to the oil and gas, and renewable sectors in the Rocky Mountain and adjacent regions, and is based in Denver, Colorado. Engineering & Technical Associates, Inc. ("ETA") —In April, 2024, the Company acquired substantially all of the assets of ETA. ETA is a niche consulting firm focusing on providing process safety management, process hazardous analysis, and other safety-focus services to industrial clients throughout the United States and Alaska. Paragon Soil and Environmental Consulting Inc. (“Paragon”) —In May 2024, the Company completed the acquisition of Paragon by acquiring 100 % of its ownership and interest. Paragon is a consulting firm that provides services for clients in the oil sands, pipeline, mining, and power sectors across western Canada. The following table summarizes the elements of the preliminary purchase price of the acquisitions completed during the six months ended June 30, 2024: Cash Common Stock Other Purchase Price Components Contingent Consideration Total Purchase Price EPIC $ 19,914 $ 4,748 $ 587 $ 11,113 $ 36,362 2DOT 39,393 1,832 ( 1,179 ) — 40,046 ETA 1,600 — 400 — 2,000 Paragon 10,982 2,691 ( 240 ) — 13,433 Total $ 71,889 $ 9,271 $ ( 432 ) $ 11,113 $ 91,841 The upfront cash payment made to acquire the acquisitions completed during the six months ended June 30, 2024 was funded through cash on hand and borrowings under our revolving credit facility. The other purchase price components mainly consist of deferred purchase price liabilities and surplus or deficit working capital amounts. The preliminary purchase price attributable to the acquisitions was allocated as follows: EPIC 2DOT ETA Paragon Total (1) Cash $ 1,045 $ 143 $ — $ 451 $ 1,639 Accounts receivable and contract assets 1,772 740 — 3,212 5,724 Other current assets 78 59 — 85 222 Current assets $ 2,895 $ 942 $ — $ 3,748 $ 7,585 Property and equipment 43 — — 330 373 Operating lease right-of-use asset 1 301 — 1,798 2,100 Customer relationships 12,327 — — — 12,327 Trade names 652 — — — 652 Covenants not to compete 1,365 — — — 1,365 Goodwill 20,842 39,388 2,000 10,563 72,793 Total assets $ 38,125 $ 40,631 $ 2,000 $ 16,439 $ 97,195 Current liabilities 1,763 392 — 1,471 3,626 Operating lease liability—net of current portion — 193 — 1,513 1,706 Other non-current liabilities — — — 22 22 Total liabilities $ 1,763 $ 585 $ — $ 3,006 $ 5,354 Purchase price $ 36,362 $ 40,046 $ 2,000 $ 13,433 $ 91,841 ___________________________________ (1) The Company is continuing to obtain information to complete the valuation of certain of these acquisitions' assets and liabilities. For the acquisitions completed during the six months ended June 30, 2024, 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 and six months ended June 30, 2024 includes revenue of $ 7.7 million and $ 11.6 million, respectively, and pre-tax income of $ 1.1 million and $ 2.4 million, respectively, related to these acquisitions. For the acquisitions completed during the six months ended June 30, 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 and six months ended June 30, 2023 includes revenue of $ 10.6 million and $ 11.6 million, respectively, and pre-tax income of $ 0.8 million and $ 1.0 million, respectively, related to these acquisitions. During the six months ended June 30, 2024, measurement period adjustments of $ 40.9 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 2024 acquisitions discussed above and all acquisitions completed in 2023 assuming they occurred on January 1, 2023. 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, 2023 nor does the information purport to reflect results for any future period. For the Three Months Ended June 30, 2024 2023 As reported Acquisitions Pro-Forma (Unaudited) Consolidated Pro-Forma (Unaudited) As reported Acquisitions Pro-Forma (Unaudited) Consolidated Pro-Forma (Unaudited) Revenues $ 173,325 $ 2,536 $ 175,861 $ 159,101 $ 18,177 $ 177,278 Net (loss) income $ ( 10,170 ) $ 436 $ ( 9,734 ) $ ( 7,174 ) $ 1,960 $ ( 5,214 ) For the Six Months Ended June 30, 2024 2023 As reported Acquisitions Pro-Forma (Unaudited) Consolidated Pro-Forma (Unaudited) As reported Acquisitions Pro-Forma (Unaudited) Consolidated Pro-Forma (Unaudited) Revenues $ 328,650 $ 7,396 $ 336,046 $ 290,529 $ 43,808 $ 334,337 Net (loss) income $ ( 23,527 ) $ 1,362 $ ( 22,165 ) $ ( 21,893 ) $ 3,703 $ ( 18,190 )

Goodwill and Intangible Assets

Goodwill and Intangible Assets	6 Months Ended
	Jun. 30, 2024
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets	8. GOODWILL AND INTANGIBLE ASSETS Amounts related to goodwill are as follows: Assessment, Permitting and Response Measurement and Analysis Remediation and Reuse Total Balance as of December 31, 2023 $ 184,946 $ 93,890 $ 85,613 $ 364,449 Goodwill acquired during the period 2,000 — 109,813 111,813 Acquisitions measurement period adjustments — — ( 39,020 ) ( 39,020 ) Prior year acquisitions measurement period adjustments — ( 844 ) ( 1,013 ) ( 1,857 ) Foreign currency translation impact — — 98 98 Balance as of June 30, 2024 $ 186,946 $ 93,046 $ 155,491 $ 435,483 Amounts related to finite-lived intangible assets are as follows: June 30, 2024 Gross Balance Accumulated Amortization Total Intangible Assets—Net Customer relationships $ 241,298 $ 127,105 $ 114,193 Covenants not to compete 37,809 32,177 5,632 Trade names 25,106 22,030 3,076 Proprietary software 27,568 20,117 7,451 Patent 17,479 4,961 12,518 Total other intangible assets, net $ 349,260 $ 206,390 $ 142,870 December 31, 2023 Gross Balance Accumulated Amortization Total Intangible Assets—Net Customer relationships $ 227,986 $ 116,226 $ 111,760 Covenants not to compete 36,250 30,889 5,361 Trade names 24,434 20,720 3,714 Proprietary software 26,486 19,309 7,177 Patent 17,479 4,678 12,801 Total other intangible assets, net $ 332,635 $ 191,822 $ 140,813 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 $ 7.1 million and $ 14.6 million for the three and six months ended June 30, 2024 , respectively, and $ 7.4 million and $ 14.6 million for the three and six months ended June 30, 2023, respectively. Future amortization expense is estimated to be as follows for each of the five following years and thereafter: December 31, 2024 (remaining) $ 15,430 2025 $ 23,024 2026 $ 18,038 2027 $ 17,201 2028 $ 14,349 Thereafter $ 54,828 Total $ 142,870

Accounts Payable and Other Accr

Accounts Payable and Other Accrued Liabilities	6 Months Ended
	Jun. 30, 2024
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: June 30, 2024 December 31, 2023 Accounts payable $ 24,294 $ 31,053 Accrued expenses 14,018 16,059 Other business acquisitions purchase price obligations 2,663 1,022 Contract liabilities 13,284 8,132 Other current liabilities 3,964 3,654 Total accounts payable and other accrued liabilities $ 58,223 $ 59,920

Accrued Payroll and Benefits

Accrued Payroll and Benefits	6 Months Ended
	Jun. 30, 2024
Statement of Financial Position [Abstract]
Accrued Payroll and Benefits	10. ACCRUED PAYROLL AND BENEFITS Accrued payroll and benefits consisted of the following: June 30, 2024 December 31, 2023 Accrued bonuses $ 7,496 $ 18,453 Accrued paid time off 5,092 1,316 Accrued payroll 11,908 11,814 Accrued other 3,843 3,077 Total accrued payroll and benefits $ 28,339 $ 34,660

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2024
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 ( 45.3 )% and ( 16.8 )% for the three and six months ended June 30, 2024, respectively, and ( 2.2 )% and ( 7.5 )% for the three and six months ended June 30, 2023, respectively. Income tax expense recorded by the Company during the three and six months ended June 30, 2024 was $ 2.6 million and $ 3.1 million, respectively. Income tax expense recorded by the Company during the three and six months ended June 30, 2023 was $ 0.2 million and $ 1.5 million, respectively. The difference between the ETR and federal statutory rate of 21.0 % is primarily attributable to items recorded for U.S. G AAP 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 June 30, 2024, 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 June 30, 2024 . The Company classifies interest and penalties recognized on uncertain tax positions as a component of income tax expense.

Debt

Debt	6 Months Ended
	Jun. 30, 2024
Debt Disclosure [Abstract]
Debt	12. DEBT Debt consisted of the following: June 30, 2024 December 31, 2023 Term loan facility $ 200,314 $ 154,219 Revolving line of credit 3,651 — Aircraft loan 9,819 10,344 Less deferred debt issuance costs ( 1,368 ) ( 1,379 ) Total debt $ 212,416 $ 163,184 Less current portion of long-term debt ( 23,667 ) ( 14,196 ) Long-term debt, less current portion $ 188,749 $ 148,988 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 2 021 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. In January 2024, the Company partially exercised its option to request an increase in the aggregate commitments to provide an additional $ 100.0 million credit availability under the 2021 Credit Facility, comprised of an additional $ 50.0 million term loan ("Additional Term Loan") and an additional $ 50.0 million in availability under the revolving line of credit. The 2021 Credit Facility term loan must be repaid in quarterly installments and shall amortize at the following future quarterly rates: Quarterly Installment Rate Date 2021 Credit Facility Term Loan Additional Term Loan June 30, 2024 1.88 % 1.25 % September 30, 2024 1.88 % 1.25 % December 31, 2024 1.88 % 1.25 % March 31, 2025 1.88 % 1.25 % June 30, 2025 1.88 % 1.25 % September 30, 2025 1.88 % 1.25 % December 31, 2025 2.50 % 1.25 % March 31, 2026 2.50 % 1.88 % April 27, 2026 Remaining balance Remaining balance Quarterly installment repayments for the three and six months ended June 30, 2024 were $ 0.6 million and $ 3.9 million, respectively. Repayment in the amount of $ 3.3 million for the second quarter was accrued as of June 30, 2024. Exclusive of the repayment made related to quarter ended March 31, 2023, quarterly installment repayments for the three and six months ended June 30, 2023 were $ 2.2 million and $ 4.4 million, respectively. On May 31, 2023, the Company amended its 2021 Credit Facility agreement to transition the reference rate from LIBOR to SOFR. The transition to SOFR did not materially impact the interest rate paid by the Company or change any material terms of the 2021 Credit Facility. The 2021 Credit Facility term loan and the revolving line of credit bear interest subject to the applicable spread based on Company’s leverage ratio and SOFR plus 0.10 % 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 On May 30, 2023, the Company amended the interest rate swap transaction it entered into on January 27, 2022 (the "2022 Interest Rate Swap"), to convert the floating component of the interest rate on $ 100.0 million of borrowings to 1-Month Term SOFR and a new coupon of 1.319 % until January 27, 2025 . Prior to the amendment, the floating component of the interest rate was subject to LIBOR and a coupon of 1.39 %. The transition to SOFR did not materially impact the interest rate paid by the Company or change any material terms of the 2022 Interest Rate Swap. On May 30, 2023, the Company entered into a second interest rate swap transaction, fixing the floating component of the interest rate on an additional $ 70.0 million of borrowings to 1-Month Term SOFR and a coupon of 3.88 % until April 27, 2026 . On June 5, 2024, the Company transitioned the 2022 Interest Rate Swap agreement of $ 100.0 million to a three-year term on $ 80.0 million of borrowings, with a fixed SOFR rate of 3.27 %. 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. In January, 2024, the Company exercised its credit facility covenant holiday, increasing its leverage capacity from 3.75 times to 4.25 times for four quarters beginning with the first quarter of 2024 . As of June 30, 2024 and December 31, 2023, the Company’s consolidated total leverage ratio (as defined in the 2021 Credit Facility) was 2.4 times and 1.9 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 six months ended June 30, 2024 and June 30, 2023 , before giving effect to the impact of the interest rate swaps, was 7.4 % and 6.3 % , respectively, and after giving effect to the impact of the interest rate swaps, was 3.4 % , and 2.1 % , 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. Loan and Aircraft Security Agreement —On May 18, 2023, the Company entered into a Loan and Aircraft Security Agreement to finance $ 10.9 million of the purchase a new aircraft (the "Aircraft Loan"). The Aircraft Loan must be repaid in 60 monthly consecutive installments and all outstanding amounts will become due on May 18, 2028. The Aircraft Loan bears interest subject to 1-Month Term SOFR and a coupon of 1.86 %. The entire principal balance may be prepaid in full subject to a 3.0 %, 2.0 % and 1.0 % prepayment fee if paid prior to the first, second and third anniversary of the loan, respectively. The aircraft serves as collateral security for the Aircraft Loan. Equipment Line of Credit —In May 2024, the Company entered into a $ 15.0 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 will expire on April 15, 2025 . Interest on leases financed under this facility is based on the SOFR swap rate on or closest to the closing date. 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. The following is a schedule of the aggregate annual maturities of long-term debt presented on the unaudited condensed consolidated statement of financial position, gross of deferred debt issuance cost of $ 1.4 million, based on the terms of the 2021 Credit Facility and the Aircraft Loan: 2021 Credit Facility June 30, Term Loan Revolver Aircraft Loan Total 2025 $ 18,907 $ 3,651 $ 1,109 $ 23,667 2026 181,407 — 1,188 182,595 2027 — — 1,273 1,273 2028 — — 6,249 6,249 Total $ 200,314 $ 3,651 $ 9,819 $ 213,784

Fair Value of Financial Instrum

Fair Value of Financial Instruments	6 Months Ended
	Jun. 30, 2024
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): June 30, 2024 December 31, 2023 Interest rate swap (1) $ 3,108 $ 3,461 Total Assets $ 3,108 $ 3,461 Business acquisitions contingent consideration, current $ 6,351 $ 3,592 Business acquisitions contingent consideration, long-term 9,595 2,448 Conversion option 19,570 19,017 Total Liabilities $ 35,516 $ 25,057 _____________________________ (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 Rate Swap Total Assets Business Acquisitions Contingent Consideration, Current Business Acquisitions Contingent Consideration, Long-term Conversion Option Total Liabilities Balance as of December 31, 2022 $ 6,046 $ 6,046 $ 3,801 $ 4,454 $ 25,731 $ 33,986 Acquisitions — — 25 — — 25 Changes in fair value included in earnings 416 416 ( 162 ) 117 1,424 1,379 Payment of contingent consideration payable — — ( 1,805 ) — — ( 1,805 ) Reclass of long term to short term contingent liabilities — — 2,260 ( 2,260 ) — — Balance as of June 30, 2023 $ 6,462 $ 6,462 $ 4,119 $ 2,311 $ 27,155 $ 33,585 Balance as of December 31, 2023 $ 3,461 $ 3,461 $ 3,592 $ 2,448 $ 19,017 $ 25,057 Acquisitions — — 4,976 6,137 11,113 Changes in fair value included in earnings ( 353 ) ( 353 ) 59 184 553 796 Payment of contingent consideration payable — — ( 1,450 ) — ( 1,450 ) Reclass of long term to short term contingent liabilities — — ( 826 ) 826 — Balance as of June 30, 2024 $ 3,108 $ 3,108 $ 6,351 $ 9,595 $ 19,570 $ 35,516

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 30, 2024
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 2029 (Note 6 and 12). Other Commitments —The Company has commitments under the 2021 Credit Facility, its Aircraft Loan, 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	6 Months Ended
	Jun. 30, 2024
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 and 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 $ 2.8 million and $ 4.1 million during the three months ended June 30, 2024 and June 30, 2023, and $ 5.6 million and $ 8.2 million during the six months ended June 30, 2024 and June 30, 2023, respectively. 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 in April 2024 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. In January 2024, the Company redeemed $ 60 million of the outstanding Convertible and Redeemable Series A-2 Preferred Stock with cash. As of June 30, 2024, the aggregate amount of the Convertible and Redeemable Series A-2 Preferred Stock issued and outstanding was $ 122.2 million, or 11,667 shares. 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 June 30, 2024, the Company has determined that a change of control is not probable. Additionally, as of June 30, 2024, 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 June 30, 2024, 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 Redeemable 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 June 30, 2024 and December 31, 2023, this conversion embedded feature had a net fair value of $ 19.6 million and $ 19.0 million, respectively. The change in net fair value of $ 0.5 million and $ 0.6 million for the three and six months ended June 30, 2024 , respectively, and $ 0.5 million and $ 1.4 million for the three and six months ended June 30, 2023 , respectively, was recorded to other expense.

Stockholder's Equity

Stockholder's Equity	6 Months Ended
	Jun. 30, 2024
Equity [Abstract]
Stockholders' Equity	16. STOCKHOLDERS’ EQUITY On April 22, 2024, the Company issued an aggregate of 3,450,000 shares of common stock in an underwritten public offering, inclusive of the shares of common stock issued in connection with the underwriters exercise in full of their option to purchase additional shares of common stock. The Company sold the shares to the underwriters at the public offering price of $ 37.15 per share, less underwriting discounts and commissions of $ 1.67175 per share, resulting in net proceeds to the Company after deducting underwriting discounts and commissions and estimated offering expenses payable by the Company of $ 121.8 million .

Net Loss Per Share

Net Loss Per Share	6 Months Ended
	Jun. 30, 2024
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 awards of restricted stock ("RSAs"), restricted stock units ("RSUs"), stock appreciation rights ("SARs") and shares of common stock underlying stock options outstanding under the Company's stock incentive plans. During the three and six months ended June 30, 2024 and June 30, 2023, 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 June 30, Six Months Ended June 30, 2024 2023 2024 2023 Net loss $ ( 10,170 ) $ ( 7,174 ) $ ( 23,527 ) $ ( 21,893 ) Convertible and redeemable series A-2 preferred stock dividend ( 2,750 ) ( 4,100 ) ( 5,564 ) ( 8,200 ) Net loss attributable to common stockholders – basic and diluted ( 12,920 ) ( 11,274 ) ( 29,091 ) ( 30,093 ) Weighted-average number of shares of common stock outstanding – basic and diluted 33,318 30,047 31,850 29,952 Net loss per share attributable to common stockholders – basic and diluted $ ( 0.39 ) $ ( 0.38 ) $ ( 0.91 ) $ ( 1.00 ) The following common stock equivalents were excluded from the calculation of dilute d net loss per share attributable to common stockholders because their effect would have been anti-dilutive: June 30, 2024 (1) 2023 (1) Stock options 3,179,129 3,436,263 Restricted stock 2,579,982 2,325,322 Series A-2 preferred stock 3,317,141 5,350,017 SARs 3,000,000 3,000,000 _____________________________ (1) Includes 6,782,913 and 7,578,724 common stock equivalents that are out of the money as of June 30, 2024 and June 30, 2023 , respectively.

Stock-Based Plans and Compensat

Stock-Based Plans and Compensation	6 Months Ended
	Jun. 30, 2024
Share-Based Payment Arrangement [Abstract]
Stock-Based Plans and Compensation	18. STOCK-BASED PLANS AND COMPENSATION 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”). The following number of shares were authorized to be issued and available for grant: June 30, 2024 2017 Plan 2013 Plan Total Shares authorized to be issued 7,538,276 2,036,219 9,574,495 Shares available for grant (1) 1,677,508 — 1,677,508 June 30, 2023 2017 Plan 2013 Plan Total Shares authorized to be issued 6,330,588 2,036,344 8,366,932 Shares available for grant (1) 750,326 — 750,326 (1) In January 2024 and January 2023 the Board of Directors ratified the addition of 1,207,563 and 1,189,801 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. There were no stock-based compensation expenses related to the 2013 Plan in the three and six months ended June 30, 2024 and 2023. Total stock-based compensation expense related to the 2017 Plan was as follows: Three Months Ended June 30, 2024 2023 Options RSUs SARs Total Options RSUs SARs Total Cost of revenue $ 355 $ 845 $ — $ 1,200 $ 466 $ 243 $ — $ 709 Selling, general and administrative expense 787 7,554 2,290 10,631 1,070 7,021 2,290 10,381 Total $ 1,142 $ 8,399 $ 2,290 $ 11,831 $ 1,536 $ 7,264 $ 2,290 $ 11,090 Six Months Ended June 30, 2024 2023 Options RSUs SARs Total Options RSUs SARs Total Cost of revenue $ 629 $ 1,482 $ — $ 2,111 $ 815 $ 786 $ — $ 1,601 Selling, general and administrative expense 1,576 14,836 4,580 20,992 2,794 15,175 4,555 22,524 Total $ 2,205 $ 16,318 $ 4,580 $ 23,103 $ 3,609 $ 15,961 $ 4,555 $ 24,125 As of June 30, 2024 and June 30, 2023, there was $ 109.6 million and $ 141.5 million, respectively, of total unrecognized stock-based compensation expense related to unvested options, restricted stock and SARs granted under the Plans. Such unrecognized expense is expected to be recognized over a weighted-average 2.5 year period. Montrose Amended & Restated 2017 Stock Incentive Plan Restricted Stock Awards and Restricted Stock Units RSAs and RSUs activity was as follows: Six Months Ended June 30, 2024 2023 Shares Weighted-Average Grant Date Fair Value Shares Weighted-Average Grant Date Fair Value Beginning outstanding shares 2,468,722 1,777,715 Granted 289,155 $ 40.58 641,282 $ 37.27 Forfeited/ cancelled ( 27,953 ) $ 37.62 ( 3,559 ) $ 32.16 Vested ( 149,942 ) $ 37.49 ( 90,116 ) $ 36.81 Ending outstanding shares 2,579,982 2,325,322 Stock Appreciation Rights As of June 30, 2024, there were 3,000,000 units of 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 June 30, 2024. 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 June 30, 2024 was 7.46 years. Options The following summarizes the options activity of the 2017 Plan: Options to Purchase Common Stock Weighted-Average Exercise Price per Share Weighted Average Grant Date Fair Value per Share Weighted Average Remaining Contract Life (in Years) Aggregate Intrinsic Value of In-The-Money Options Outstanding as of December 31, 2022 2,579,566 $ 31.00 $ 15.00 7.8 $ 37,292 Granted 233,955 32.16 13.90 — — Forfeited/ cancelled ( 63,085 ) 37.41 — — — Expired ( 1,200 ) 25.05 — — — Exercised ( 125,229 ) 23.76 — — 2,794 Outstanding as of June 30, 2023 2,624,007 $ 30.88 $ 15.62 7.5 $ 32,414 Outstanding as of December 31, 2023 2,516,272 $ 30.92 $ 15.95 7.0 $ 13,825 Forfeited/ cancelled ( 48,765 ) 38.87 — — — Expired ( 19,720 ) 45.55 — — — Exercised ( 47,948 ) 27.05 — — 663 Outstanding as of June 30, 2024 2,399,839 $ 30.72 $ 16.27 7.0 $ 14,488 Exercisable as of June 30, 2024 1,484,676 $ 31.13 6.2 $ 20,723 The following weighted-average assumptions were used in the Black-Scholes option-pricing model calculation: June 30, 2023 Common stock value (per share) $ 32.16 Expected volatility 33.79 % Risk-free interest rate 3.72 % Expected life (years) 7.00 Forfeiture rate None Dividend rate None Montrose Amended & Restated 2013 Stock Option Plan The following summarizes the activity of the 2013 Plan: Options to Purchase Common Stock Weighted-Average Exercise Price per Share Weighted Average Grant Date Fair Value per Share Weighted Average Remaining Contract Life (in Years) Aggregate Intrinsic Value of In-The-Money Options Outstanding as of December 31, 2022 855,695 $ 6.00 $ 2.00 3.3 $ 32,478 Expired ( 675 ) 6.03 — — — Exercised ( 42,764 ) 7.47 — — 1,514 Outstanding as of June 30, 2023 812,256 $ 6.38 $ 2.11 2.8 $ 29,030 Outstanding as of December 31, 2023 792,191 $ 6.40 $ 2.16 2.4 $ 20,380 Exercised ( 12,901 ) 6.08 Outstanding as of June 30, 2024 779,290 $ 6.41 $ 2.20 1.9 $ 29,730 Exercisable as of June 30, 2024 779,290 $ 6.41 1.9 $ 29,730 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: June 30, 2024 2023 Montrose 2013 Stock Incentive Plan 779,290 812,256 Montrose 2017 Stock Incentive Plan (1) 9,657,329 8,699,655 10,436,619 9,511,911 (1) In January 2024 and 2023, the Board of Directors ratified the addition of 1,207,563 and 1,189,801 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. 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.

Segment Information

Segment Information	6 Months Ended
	Jun. 30, 2024
Segment Reporting [Abstract]
Segment Information	19. 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, types of customers, methods used to distribute the products and the nature of the regulatory environment. Our Chief Executive Officer, who serves as the Chief Operating Decision Maker ("CODM"), reviews Segment Adjusted EBITDA as 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 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 discontinue one of its non-core specialty service lines within the lab testing business (the "Discontinued Specialty Lab"). On December 29, 2023, the Company sold the assets of the Discontinued Specialty Lab for a total sales price of $ 4.8 million, of which $ 0.5 million was received in cash and $ 4.3 million was issued as a promissory note receivable. The promissory note receivable is subject to an annual 9.0 % interest rate and will be repaid in 60 monthly installments with the remaining balance payable in full on December 29, 2028. The promissory note receivable balance, net of expected loss and payment, was $ 2.1 million as of June 30, 2024 and December 31, 2023, respectively. The discontinuation of this specialty service line, which was part of the Company's Measurement and Analysis segment, did not represent a strategic shift that had 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 June 30, 2024 2023 Segment Revenues Segment Adjusted EBITDA Segment Revenues Segment Adjusted EBITDA Assessment, Permitting and Response $ 53,444 $ 12,621 $ 61,411 $ 13,833 Measurement and Analysis 54,812 12,359 50,055 10,789 Remediation and Reuse 65,069 8,929 47,635 6,043 Total Operating Segments $ 173,325 $ 33,909 $ 159,101 $ 30,665 Corporate and Other — ( 10,593 ) — ( 9,474 ) Total $ 173,325 $ 23,316 $ 159,101 $ 21,191 Six Months Ended June 30, 2024 2023 Segment Revenues Segment Adjusted EBITDA Segment Revenues Segment Adjusted EBITDA Assessment, Permitting and Response $ 112,024 $ 28,901 $ 113,625 $ 28,099 Measurement and Analysis 100,306 18,863 92,582 17,176 Remediation and Reuse 116,320 13,940 84,322 11,321 Total Operating Segments $ 328,650 $ 61,704 $ 290,529 $ 56,596 Corporate and Other — ( 21,466 ) — ( 18,802 ) Total $ 328,650 $ 40,238 $ 290,529 $ 37,794 Presented below is a reconciliation of the Company’s segment measure to net loss: For the Three Months Ended June 30, For the Six Months Ended June 30, 2024 2023 2024 2023 Adjusted EBITDA $ 23,316 $ 21,191 $ 40,238 $ 37,794 Interest expense, net ( 3,976 ) ( 1,877 ) ( 7,282 ) ( 3,418 ) Income tax expense ( 2,619 ) ( 151 ) ( 3,112 ) ( 1,518 ) Depreciation and amortization ( 12,515 ) ( 11,398 ) ( 24,168 ) ( 21,953 ) Stock-based compensation ( 11,831 ) ( 11,090 ) ( 23,103 ) ( 24,125 ) Acquisition costs ( 1,082 ) ( 2,696 ) ( 3,607 ) ( 3,471 ) Fair value changes in financial instruments ( 1,202 ) 865 ( 905 ) ( 1,008 ) Fair value changes in business acquisition contingencies ( 136 ) ( 353 ) ( 242 ) 45 Expenses related to financing transactions ( 95 ) — ( 239 ) ( 4 ) Discontinued Specialty Lab — ( 1,583 ) (1) ( 596 ) (1) ( 4,019 ) (1) Other losses or expenses ( 30 ) ( 82 ) ( 511 ) (2) ( 216 ) Net loss $ ( 10,170 ) $ ( 7,174 ) $ ( 23,527 ) $ ( 21,893 ) __________________________ (1) Amounts consist of operating losses before depreciation related to the Discontinued Specialty Lab. (2) Amount consists of costs associated with a lease abandonment. The following table presents revenues by geograph ic location: For the Three Months Ended June 30, For the Six Months Ended June 30, 2024 2023 2024 2023 United States $ 137,012 $ 145,162 $ 265,854 $ 271,944 Canada 28,597 11,407 49,878 13,283 Other international 7,716 2,532 12,918 5,302 Total revenue $ 173,325 $ 159,101 $ 328,650 $ 290,529

Related-Party Transactions

Related-Party Transactions	6 Months Ended
	Jun. 30, 2024
Related Party Transactions [Abstract]
Related-Party Transactions	20. RELATED-PARTY TRANSACTIONS The Company d id no t ha ve any related party transactions during the three and six months ended June 30, 2024 and June 30, 2023 .

Defined Contribution Plan

Defined Contribution Plan	6 Months Ended
	Jun. 30, 2024
Retirement Benefits [Abstract]
Defined Contribution Plan	21. 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 June 30, 2024, and December 31, 2023 , 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 were $ 8.9 million and $ 11.6 million for the three and six months ended June 30, 2024 , respectively, and $ 1.8 million and $ 3.9 million for the three and six months ended June 30, 2023 , respectively, and are included within selling, general, and administrative expense on the unaudited condensed consolidated statements of operations.

Subsequent Events

Subsequent Events	6 Months Ended
	Jun. 30, 2024
Subsequent Events [Abstract]
Subsequent Events	22. SUBSEQUENT EVENTS Spirit Acquisition On July 1, 2024 , the Company acquired substantially all of the assets of Spirit Environmental, LLC ("Spirit"), a highly reputable provider of air permitting, compliance, and environmental services. The purchase price was $ 17.5 million, of which $ 16.0 million was funded with cash on hand, and the remaining $ 1.5 million was paid in the Company's common stock.

Description of the Business a_2

Description of the Business and Basis of Presentation (Policies)	6 Months Ended
	Jun. 30, 2024
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, 2023. 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. Within the unaudited condensed consolidated financial statements certain amounts in the prior period have been reclassified to conform with current period presentation. The Company reclassified $ 1.8 million of provision for bad debt, $ 0.9 million of fair value changes, $ 1.5 million of deferred income taxes, and $ 1.1 million of other activities to other operating activities, net, in the condensed consolidated statements of cash flows for the six months ended June 30, 2023. The Company disaggregated 130,115 shares or $ 3.2 million of common stock issued for quarter ended June 30, 2023, and 427,631 shares or $ 8.2 million of common stock issued for quarter ended March 31, 2024 to separate line items on the condensed consolidated statements of convertible and redeemable series A-2 preferred stock and stockholders’ equity. These changes had no effect on the Company's results of operations or financial position.
Recently Adopted Accounting Pronouncements /Recently Issued Accounting Pronouncements Not Yet Adopted	Recently Adopted Accounting Pronouncements In November 2023, the Financial Accounting Standards Board ("FASB") issued Accounting Standard Update ("ASU") 2023-07, Improvements to Reportable Segment Disclosures. The amendments improve reportable segment disclosure requirements, primarily through enhanced disclosures about significant segment expenses. In addition, the amendments enhance interim disclosure requirements, clarify circumstances in which an entity can disclose multiple segment measures of profit or loss, provide new segment disclosure requirements for entities with a single reportable segment, and contain other disclosure requirements. The purpose of the amendments is to enable investors to better understand an entity’s overall performance and assess potential future cash flows. ASU 2023-07 is effective for the Company's fiscal year beginning January 1, 2024 and requires the use of a retrospective approach to all prior periods presented. The Company adopted the standard on January 1, 2024 , and plans to adopt the standard for interim periods beginning January 1, 2025. The Company is evaluating the potential impact of its adoption of ASU 2023-07 on the Company's audited Consolidated Financial Statements but does not anticipate that such an adoption will have a material impact. Recently Issued Accounting Pronouncements Not Yet Adopted In August 2023, the FASB issued ASU 2023-05, under which an entity that qualifies as either a joint venture or a corporate joint venture is required to apply a new basis of accounting upon the formation of the joint venture. Specifically, the ASU provides that a joint venture or a corporate joint venture must initially measure its assets and liabilities at fair value on the formation date. The amendments in ASU 2023-05 are effective for all joint ventures within the ASU’s scope that are formed on or after January 1, 2025. Early adoption is permitted. The Company is currently evaluating the impact of the adoption of the standard on its consolidated financial statements. In December 2023, the FASB issued ASU 2023-09, Improvements to Income Tax Disclosures, which improves the transparency of income tax disclosures by requiring consistent categories and greater disaggregation of information in the rate reconciliation and income taxes paid disaggregated by jurisdiction. It also includes certain other amendments to improve the effectiveness of income tax disclosures. ASU 2023-09 is effective for the Company beginning January 1, 2025 and allows the use of a prospective or retrospective approach. The Company is currently evaluating the impact of the adoption of the standard on its consolidated financial statements.

Revenues and Accounts Receiva_2

Revenues and Accounts Receivable (Tables)	6 Months Ended
	Jun. 30, 2024
Revenues And Accounts Receivable [Abstract]
Schedule of Contract Balances	The following table presents the Company’s contract balances: June 30, December 31, 2024 2023 Contract assets $ 73,224 $ 51,629 Contract liabilities 13,284 8,132
Schedule of Accounts Receivable, Net	Accounts Receivable, Net Accounts receivable, net consisted of the following: June 30, 2024 December 31, 2023 Accounts receivable, invoiced $ 136,972 $ 115,064 Accounts receivable, other 1,481 20 Allowance for doubtful accounts ( 2,784 ) ( 2,724 ) Accounts receivable, net $ 135,669 $ 112,360
Schedule of Allowance for Doubtful Accounts	The allowance for doubtful accounts consisted of the following: Beginning Bad Debt Charged to Other (1) Ending Six months ended June 30, 2024 $ 2,724 $ ( 659 ) $ ( 11 ) $ 730 $ 2,784 Year ended December 31, 2023 1,915 3,142 ( 2,333 ) — 2,724 ____________________ (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)	6 Months Ended
	Jun. 30, 2024
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: June 30, 2024 December 31, 2023 Deposits $ 1,412 $ 1,764 Prepaid expenses 9,831 8,112 Supplies 2,979 3,819 Prepaid and other current assets $ 14,222 $ 13,695

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	6 Months Ended
	Jun. 30, 2024
Property, Plant and Equipment [Abstract]
Property and Equipment, Net	Property and equipment, net, consisted of the following: June 30, 2024 December 31, 2023 Lab and test equipment $ 20,989 $ 20,341 Vehicles 6,096 6,033 Equipment 54,782 50,387 Furniture and fixtures 3,001 2,963 Leasehold improvements 12,444 10,808 Aircraft 12,386 12,312 Building 5,748 5,748 115,446 108,592 Land 1,089 1,089 Construction in progress 10,497 3,956 Less: Accumulated depreciation ( 63,405 ) ( 56,812 ) Total property and equipment—net $ 63,627 $ 56,825

Leases (Tables)

Leases (Tables)	6 Months Ended
	Jun. 30, 2024
Leases [Abstract]
Summary of Components of Lease Expense	The components of lease expense were as follows: For the Three Months Ended June 30, Statement of Operations Location 2024 2023 Operating lease cost Lease cost Selling, general and administrative expense $ 2,956 $ 2,804 Variable lease cost Selling, general and administrative expense 580 299 Total operating lease cost $ 3,536 $ 3,103 Finance lease cost Amortization of right of use assets Depreciation and amortization $ 1,293 $ 1,429 Interest on lease liabilities Interest expense, net 204 171 Total finance lease cost $ 1,497 $ 1,600 Total lease cost $ 5,033 $ 4,703 For the Six Months Ended June 30, Statement of Operations Location 2024 2023 Operating lease cost Lease cost Selling, general and administrative expense $ 5,950 $ 5,545 Variable lease cost Selling, general and administrative expense 1,036 625 Total operating lease cost $ 6,986 $ 6,170 Finance lease cost Amortization of right of use assets Depreciation and amortization $ 2,571 $ 2,583 Interest on lease liabilities Interest expense, net 399 301 Total finance lease cost $ 2,970 $ 2,884 Total lease cost $ 9,956 $ 9,054
Summary of Supplemental Cash Flow Information Related To Leases	Supplemental cash flows information related to leases was as follows: For the Six Months Ended June 30, 2024 2023 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows used in operating leases $ 6,170 $ 5,306 Operating cash flows used in finance leases 399 301 Financing cash flows used in finance leases 3,103 2,198 Lease liabilities arising from new ROU assets: Operating leases 9,694 23,831 Finance leases 2,666 3,326
Summary of Weighted Average Remaining Lease Terms and Weighted Average Discount Rates	Weighted average remaining lease terms and weighted average discount rates were: June 30, 2024 Operating Leases Finance Leases Weighted average remaining lease term (years) 4.4 3.4 Weighted average discount rate 4.4 % 6.5 % June 30, 2023 Operating Leases Finance Leases Weighted average remaining lease term (years) 5.5 3.3 Weighted average discount rate 2.8 % 5.8 %
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 2024 $ 6,623 $ 2,547 2025 11,643 4,072 2026 9,342 3,409 2027 6,484 2,408 2028 5,029 1,244 2029 and thereafter 6,362 — Total undiscounted future minimum lease payments $ 45,483 $ 13,680 Less imputed interest ( 4,347 ) ( 1,452 ) Total discounted future minimum lease payments $ 41,136 $ 12,228

Business Acquisitions (Tables)

Business Acquisitions (Tables)	6 Months Ended
	Jun. 30, 2024
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 2024 acquisitions discussed above and all acquisitions completed in 2023 assuming they occurred on January 1, 2023. 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, 2023 nor does the information purport to reflect results for any future period. For the Three Months Ended June 30, 2024 2023 As reported Acquisitions Pro-Forma (Unaudited) Consolidated Pro-Forma (Unaudited) As reported Acquisitions Pro-Forma (Unaudited) Consolidated Pro-Forma (Unaudited) Revenues $ 173,325 $ 2,536 $ 175,861 $ 159,101 $ 18,177 $ 177,278 Net (loss) income $ ( 10,170 ) $ 436 $ ( 9,734 ) $ ( 7,174 ) $ 1,960 $ ( 5,214 ) For the Six Months Ended June 30, 2024 2023 As reported Acquisitions Pro-Forma (Unaudited) Consolidated Pro-Forma (Unaudited) As reported Acquisitions Pro-Forma (Unaudited) Consolidated Pro-Forma (Unaudited) Revenues $ 328,650 $ 7,396 $ 336,046 $ 290,529 $ 43,808 $ 334,337 Net (loss) income $ ( 23,527 ) $ 1,362 $ ( 22,165 ) $ ( 21,893 ) $ 3,703 $ ( 18,190 )
EPIC, Two Dot
Business Acquisition [Line Items]
Summary of Main Elements of Preliminary Purchase Price of Acquisitions	The following table summarizes the elements of the preliminary purchase price of the acquisitions completed during the six months ended June 30, 2024: Cash Common Stock Other Purchase Price Components Contingent Consideration Total Purchase Price EPIC $ 19,914 $ 4,748 $ 587 $ 11,113 $ 36,362 2DOT 39,393 1,832 ( 1,179 ) — 40,046 ETA 1,600 — 400 — 2,000 Paragon 10,982 2,691 ( 240 ) — 13,433 Total $ 71,889 $ 9,271 $ ( 432 ) $ 11,113 $ 91,841
Summary of Purchase Price Attributable to Acquisitions	The preliminary purchase price attributable to the acquisitions was allocated as follows: EPIC 2DOT ETA Paragon Total (1) Cash $ 1,045 $ 143 $ — $ 451 $ 1,639 Accounts receivable and contract assets 1,772 740 — 3,212 5,724 Other current assets 78 59 — 85 222 Current assets $ 2,895 $ 942 $ — $ 3,748 $ 7,585 Property and equipment 43 — — 330 373 Operating lease right-of-use asset 1 301 — 1,798 2,100 Customer relationships 12,327 — — — 12,327 Trade names 652 — — — 652 Covenants not to compete 1,365 — — — 1,365 Goodwill 20,842 39,388 2,000 10,563 72,793 Total assets $ 38,125 $ 40,631 $ 2,000 $ 16,439 $ 97,195 Current liabilities 1,763 392 — 1,471 3,626 Operating lease liability—net of current portion — 193 — 1,513 1,706 Other non-current liabilities — — — 22 22 Total liabilities $ 1,763 $ 585 $ — $ 3,006 $ 5,354 Purchase price $ 36,362 $ 40,046 $ 2,000 $ 13,433 $ 91,841 ___________________________________ (1) The Company is continuing to obtain information to complete the valuation of certain of these acquisitions' assets and liabilities.

Goodwill and Intangible Assets

Goodwill and Intangible Assets (Tables)	6 Months Ended
	Jun. 30, 2024
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Amounts Related to Goodwill	Amounts related to goodwill are as follows: Assessment, Permitting and Response Measurement and Analysis Remediation and Reuse Total Balance as of December 31, 2023 $ 184,946 $ 93,890 $ 85,613 $ 364,449 Goodwill acquired during the period 2,000 — 109,813 111,813 Acquisitions measurement period adjustments — — ( 39,020 ) ( 39,020 ) Prior year acquisitions measurement period adjustments — ( 844 ) ( 1,013 ) ( 1,857 ) Foreign currency translation impact — — 98 98 Balance as of June 30, 2024 $ 186,946 $ 93,046 $ 155,491 $ 435,483
Schedule of Amounts Related to Finite-Lived Intangible Assets	Amounts related to finite-lived intangible assets are as follows: June 30, 2024 Gross Balance Accumulated Amortization Total Intangible Assets—Net Customer relationships $ 241,298 $ 127,105 $ 114,193 Covenants not to compete 37,809 32,177 5,632 Trade names 25,106 22,030 3,076 Proprietary software 27,568 20,117 7,451 Patent 17,479 4,961 12,518 Total other intangible assets, net $ 349,260 $ 206,390 $ 142,870 December 31, 2023 Gross Balance Accumulated Amortization Total Intangible Assets—Net Customer relationships $ 227,986 $ 116,226 $ 111,760 Covenants not to compete 36,250 30,889 5,361 Trade names 24,434 20,720 3,714 Proprietary software 26,486 19,309 7,177 Patent 17,479 4,678 12,801 Total other intangible assets, net $ 332,635 $ 191,822 $ 140,813
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, 2024 (remaining) $ 15,430 2025 $ 23,024 2026 $ 18,038 2027 $ 17,201 2028 $ 14,349 Thereafter $ 54,828 Total $ 142,870

Accounts Payable and Other Ac_2

Accounts Payable and Other Accrued Liabilities (Tables)	6 Months Ended
	Jun. 30, 2024
Payables and Accruals [Abstract]
Summary of Accounts Payable and Other Accrued Liabilities	Accounts payable and other accrued liabilities consisted of the following: June 30, 2024 December 31, 2023 Accounts payable $ 24,294 $ 31,053 Accrued expenses 14,018 16,059 Other business acquisitions purchase price obligations 2,663 1,022 Contract liabilities 13,284 8,132 Other current liabilities 3,964 3,654 Total accounts payable and other accrued liabilities $ 58,223 $ 59,920

Accrued Payroll and Benefits (T

Accrued Payroll and Benefits (Tables)	6 Months Ended
	Jun. 30, 2024
Statement of Financial Position [Abstract]
Schedule of Accrued Payroll and Benefits	Accrued payroll and benefits consisted of the following: June 30, 2024 December 31, 2023 Accrued bonuses $ 7,496 $ 18,453 Accrued paid time off 5,092 1,316 Accrued payroll 11,908 11,814 Accrued other 3,843 3,077 Total accrued payroll and benefits $ 28,339 $ 34,660

Debt (Tables)

Debt (Tables)	6 Months Ended
	Jun. 30, 2024
Debt Disclosure [Abstract]
Schedule of Debt	Debt consisted of the following: June 30, 2024 December 31, 2023 Term loan facility $ 200,314 $ 154,219 Revolving line of credit 3,651 — Aircraft loan 9,819 10,344 Less deferred debt issuance costs ( 1,368 ) ( 1,379 ) Total debt $ 212,416 $ 163,184 Less current portion of long-term debt ( 23,667 ) ( 14,196 ) Long-term debt, less current portion $ 188,749 $ 148,988
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: Quarterly Installment Rate Date 2021 Credit Facility Term Loan Additional Term Loan June 30, 2024 1.88 % 1.25 % September 30, 2024 1.88 % 1.25 % December 31, 2024 1.88 % 1.25 % March 31, 2025 1.88 % 1.25 % June 30, 2025 1.88 % 1.25 % September 30, 2025 1.88 % 1.25 % December 31, 2025 2.50 % 1.25 % March 31, 2026 2.50 % 1.88 % April 27, 2026 Remaining balance Remaining balance
Summary of 2021 Credit Facility Interest Rate Subject to Leverage Ratio and SOFR	The 2021 Credit Facility term loan and the revolving line of credit bear interest subject to the applicable spread based on Company’s leverage ratio and SOFR plus 0.10 % 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, gross of deferred debt issuance cost of $ 1.4 million, based on the terms of the 2021 Credit Facility and the Aircraft Loan: 2021 Credit Facility June 30, Term Loan Revolver Aircraft Loan Total 2025 $ 18,907 $ 3,651 $ 1,109 $ 23,667 2026 181,407 — 1,188 182,595 2027 — — 1,273 1,273 2028 — — 6,249 6,249 Total $ 200,314 $ 3,651 $ 9,819 $ 213,784

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	6 Months Ended
	Jun. 30, 2024
Fair Value Disclosures [Abstract]
Summary of Financial Instruments Measured at Fair Value on Recurring Basis using Significant Unobservable Inputs (Level 3)	The following financial instruments are measured at fair value on a recurring basis using significant unobservable inputs (Level 3): June 30, 2024 December 31, 2023 Interest rate swap (1) $ 3,108 $ 3,461 Total Assets $ 3,108 $ 3,461 Business acquisitions contingent consideration, current $ 6,351 $ 3,592 Business acquisitions contingent consideration, long-term 9,595 2,448 Conversion option 19,570 19,017 Total Liabilities $ 35,516 $ 25,057 _____________________________ (1) Included in other assets in the unaudited condensed consolidated statement of financial position.
Summary of Financial Instruments Measured at Fair Value on Recurring Basis	The following table sets forth the Company’s financial instruments that were measured at fair value on a recurring basis: Interest Rate Swap Total Assets Business Acquisitions Contingent Consideration, Current Business Acquisitions Contingent Consideration, Long-term Conversion Option Total Liabilities Balance as of December 31, 2022 $ 6,046 $ 6,046 $ 3,801 $ 4,454 $ 25,731 $ 33,986 Acquisitions — — 25 — — 25 Changes in fair value included in earnings 416 416 ( 162 ) 117 1,424 1,379 Payment of contingent consideration payable — — ( 1,805 ) — — ( 1,805 ) Reclass of long term to short term contingent liabilities — — 2,260 ( 2,260 ) — — Balance as of June 30, 2023 $ 6,462 $ 6,462 $ 4,119 $ 2,311 $ 27,155 $ 33,585 Balance as of December 31, 2023 $ 3,461 $ 3,461 $ 3,592 $ 2,448 $ 19,017 $ 25,057 Acquisitions — — 4,976 6,137 11,113 Changes in fair value included in earnings ( 353 ) ( 353 ) 59 184 553 796 Payment of contingent consideration payable — — ( 1,450 ) — ( 1,450 ) Reclass of long term to short term contingent liabilities — — ( 826 ) 826 — Balance as of June 30, 2024 $ 3,108 $ 3,108 $ 6,351 $ 9,595 $ 19,570 $ 35,516

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	6 Months Ended
	Jun. 30, 2024
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 June 30, Six Months Ended June 30, 2024 2023 2024 2023 Net loss $ ( 10,170 ) $ ( 7,174 ) $ ( 23,527 ) $ ( 21,893 ) Convertible and redeemable series A-2 preferred stock dividend ( 2,750 ) ( 4,100 ) ( 5,564 ) ( 8,200 ) Net loss attributable to common stockholders – basic and diluted ( 12,920 ) ( 11,274 ) ( 29,091 ) ( 30,093 ) Weighted-average number of shares of common stock outstanding – basic and diluted 33,318 30,047 31,850 29,952 Net loss per share attributable to common stockholders – basic and diluted $ ( 0.39 ) $ ( 0.38 ) $ ( 0.91 ) $ ( 1.00 )
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 dilute d net loss per share attributable to common stockholders because their effect would have been anti-dilutive: June 30, 2024 (1) 2023 (1) Stock options 3,179,129 3,436,263 Restricted stock 2,579,982 2,325,322 Series A-2 preferred stock 3,317,141 5,350,017 SARs 3,000,000 3,000,000 _____________________________ (1) Includes 6,782,913 and 7,578,724 common stock equivalents that are out of the money as of June 30, 2024 and June 30, 2023 , respectively.

Stock-Based Plans and Compens_2

Stock-Based Plans and Compensation (Tables)	6 Months Ended
	Jun. 30, 2024
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: June 30, 2024 2017 Plan 2013 Plan Total Shares authorized to be issued 7,538,276 2,036,219 9,574,495 Shares available for grant (1) 1,677,508 — 1,677,508 June 30, 2023 2017 Plan 2013 Plan Total Shares authorized to be issued 6,330,588 2,036,344 8,366,932 Shares available for grant (1) 750,326 — 750,326 (1) In January 2024 and January 2023 the Board of Directors ratified the addition of 1,207,563 and 1,189,801 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-based Compensation Expense	There were no stock-based compensation expenses related to the 2013 Plan in the three and six months ended June 30, 2024 and 2023. Total stock-based compensation expense related to the 2017 Plan was as follows: Three Months Ended June 30, 2024 2023 Options RSUs SARs Total Options RSUs SARs Total Cost of revenue $ 355 $ 845 $ — $ 1,200 $ 466 $ 243 $ — $ 709 Selling, general and administrative expense 787 7,554 2,290 10,631 1,070 7,021 2,290 10,381 Total $ 1,142 $ 8,399 $ 2,290 $ 11,831 $ 1,536 $ 7,264 $ 2,290 $ 11,090 Six Months Ended June 30, 2024 2023 Options RSUs SARs Total Options RSUs SARs Total Cost of revenue $ 629 $ 1,482 $ — $ 2,111 $ 815 $ 786 $ — $ 1,601 Selling, general and administrative expense 1,576 14,836 4,580 20,992 2,794 15,175 4,555 22,524 Total $ 2,205 $ 16,318 $ 4,580 $ 23,103 $ 3,609 $ 15,961 $ 4,555 $ 24,125
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-Scholes option-pricing model calculation: June 30, 2023 Common stock value (per share) $ 32.16 Expected volatility 33.79 % Risk-free interest rate 3.72 % Expected life (years) 7.00 Forfeiture rate None Dividend rate 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: June 30, 2024 2023 Montrose 2013 Stock Incentive Plan 779,290 812,256 Montrose 2017 Stock Incentive Plan (1) 9,657,329 8,699,655 10,436,619 9,511,911 (1) In January 2024 and 2023, the Board of Directors ratified the addition of 1,207,563 and 1,189,801 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. 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: Six Months Ended June 30, 2024 2023 Shares Weighted-Average Grant Date Fair Value Shares Weighted-Average Grant Date Fair Value Beginning outstanding shares 2,468,722 1,777,715 Granted 289,155 $ 40.58 641,282 $ 37.27 Forfeited/ cancelled ( 27,953 ) $ 37.62 ( 3,559 ) $ 32.16 Vested ( 149,942 ) $ 37.49 ( 90,116 ) $ 36.81 Ending outstanding shares 2,579,982 2,325,322
Summary of Stock Option Activity	The following summarizes the options activity of the 2017 Plan: Options to Purchase Common Stock Weighted-Average Exercise Price per Share Weighted Average Grant Date Fair Value per Share Weighted Average Remaining Contract Life (in Years) Aggregate Intrinsic Value of In-The-Money Options Outstanding as of December 31, 2022 2,579,566 $ 31.00 $ 15.00 7.8 $ 37,292 Granted 233,955 32.16 13.90 — — Forfeited/ cancelled ( 63,085 ) 37.41 — — — Expired ( 1,200 ) 25.05 — — — Exercised ( 125,229 ) 23.76 — — 2,794 Outstanding as of June 30, 2023 2,624,007 $ 30.88 $ 15.62 7.5 $ 32,414 Outstanding as of December 31, 2023 2,516,272 $ 30.92 $ 15.95 7.0 $ 13,825 Forfeited/ cancelled ( 48,765 ) 38.87 — — — Expired ( 19,720 ) 45.55 — — — Exercised ( 47,948 ) 27.05 — — 663 Outstanding as of June 30, 2024 2,399,839 $ 30.72 $ 16.27 7.0 $ 14,488 Exercisable as of June 30, 2024 1,484,676 $ 31.13 6.2 $ 20,723
Montrose Amended and Restated 2013 Stock Option Plan
Summary of Stock Option Activity	The following summarizes the activity of the 2013 Plan: Options to Purchase Common Stock Weighted-Average Exercise Price per Share Weighted Average Grant Date Fair Value per Share Weighted Average Remaining Contract Life (in Years) Aggregate Intrinsic Value of In-The-Money Options Outstanding as of December 31, 2022 855,695 $ 6.00 $ 2.00 3.3 $ 32,478 Expired ( 675 ) 6.03 — — — Exercised ( 42,764 ) 7.47 — — 1,514 Outstanding as of June 30, 2023 812,256 $ 6.38 $ 2.11 2.8 $ 29,030 Outstanding as of December 31, 2023 792,191 $ 6.40 $ 2.16 2.4 $ 20,380 Exercised ( 12,901 ) 6.08 Outstanding as of June 30, 2024 779,290 $ 6.41 $ 2.20 1.9 $ 29,730 Exercisable as of June 30, 2024 779,290 $ 6.41 1.9 $ 29,730

Segment Information (Tables)

Segment Information (Tables)	6 Months Ended
	Jun. 30, 2024
Segment Reporting [Abstract]
Components of Segment Revenues and Adjusted EBITDA	Segment revenues and Adjusted EBITDA consisted of the following: Three Months Ended June 30, 2024 2023 Segment Revenues Segment Adjusted EBITDA Segment Revenues Segment Adjusted EBITDA Assessment, Permitting and Response $ 53,444 $ 12,621 $ 61,411 $ 13,833 Measurement and Analysis 54,812 12,359 50,055 10,789 Remediation and Reuse 65,069 8,929 47,635 6,043 Total Operating Segments $ 173,325 $ 33,909 $ 159,101 $ 30,665 Corporate and Other — ( 10,593 ) — ( 9,474 ) Total $ 173,325 $ 23,316 $ 159,101 $ 21,191 Six Months Ended June 30, 2024 2023 Segment Revenues Segment Adjusted EBITDA Segment Revenues Segment Adjusted EBITDA Assessment, Permitting and Response $ 112,024 $ 28,901 $ 113,625 $ 28,099 Measurement and Analysis 100,306 18,863 92,582 17,176 Remediation and Reuse 116,320 13,940 84,322 11,321 Total Operating Segments $ 328,650 $ 61,704 $ 290,529 $ 56,596 Corporate and Other — ( 21,466 ) — ( 18,802 ) Total $ 328,650 $ 40,238 $ 290,529 $ 37,794
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 Ended June 30, For the Six Months Ended June 30, 2024 2023 2024 2023 Adjusted EBITDA $ 23,316 $ 21,191 $ 40,238 $ 37,794 Interest expense, net ( 3,976 ) ( 1,877 ) ( 7,282 ) ( 3,418 ) Income tax expense ( 2,619 ) ( 151 ) ( 3,112 ) ( 1,518 ) Depreciation and amortization ( 12,515 ) ( 11,398 ) ( 24,168 ) ( 21,953 ) Stock-based compensation ( 11,831 ) ( 11,090 ) ( 23,103 ) ( 24,125 ) Acquisition costs ( 1,082 ) ( 2,696 ) ( 3,607 ) ( 3,471 ) Fair value changes in financial instruments ( 1,202 ) 865 ( 905 ) ( 1,008 ) Fair value changes in business acquisition contingencies ( 136 ) ( 353 ) ( 242 ) 45 Expenses related to financing transactions ( 95 ) — ( 239 ) ( 4 ) Discontinued Specialty Lab — ( 1,583 ) (1) ( 596 ) (1) ( 4,019 ) (1) Other losses or expenses ( 30 ) ( 82 ) ( 511 ) (2) ( 216 ) Net loss $ ( 10,170 ) $ ( 7,174 ) $ ( 23,527 ) $ ( 21,893 ) __________________________ (1) Amounts consist of operating losses before depreciation related to the Discontinued Specialty Lab. (2) Amount consists of costs associated with a lease abandonment.
Schedule of Revenues by Geographic Location	The following table presents revenues by geograph ic location: For the Three Months Ended June 30, For the Six Months Ended June 30, 2024 2023 2024 2023 United States $ 137,012 $ 145,162 $ 265,854 $ 271,944 Canada 28,597 11,407 49,878 13,283 Other international 7,716 2,532 12,918 5,302 Total revenue $ 173,325 $ 159,101 $ 328,650 $ 290,529

Description of the Business a_3

Description of the Business and Basis of Presentation - Additional Information (Details) $ in Thousands	3 Months Ended			6 Months Ended		12 Months Ended
	Jun. 30, 2024 USD ($) Employee shares	Mar. 31, 2024 USD ($) shares	Jun. 30, 2023 USD ($) shares	Jun. 30, 2024 USD ($) Employee Office Segment	Jun. 30, 2023 USD ($)	Dec. 31, 2023 USD ($)
Description Of Business And Basis Of Presentation [Line Items]
Entity formation, month and year				2013-11
Number of offices in which entity operates | Office				110
Entity number of employees | Employee	3,380			3,380
Number of operating segments | Segment				3
Provision for bad debt				$ (659)		$ 3,142
Changes in fair value	$ (1,202)		$ 865	(905)	$ (1,008)
Other operating activities, net				4,121	$ 5,439
Common Stock
Description Of Business And Basis Of Presentation [Line Items]
Common stock issued, shares | shares	3,450,000	427,631	130,115
Common stock issued		$ 8,200	$ 3,200
Reclassification Adjustment
Description Of Business And Basis Of Presentation [Line Items]
Provision for bad debt				1,800
Changes in fair value				900
Deferred income taxes				1,500
Other operating activities, net				$ 1,100

Summary of New Accounting Pro_2

Summary of New Accounting Pronouncements - Additional Information (Details) - Accounting Standards Update 2023-07	Jun. 30, 2024
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, 2024
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	Jun. 30, 2024	Dec. 31, 2023
Revenues And Accounts Receivable [Abstract]
Contract assets	$ 73,224	$ 51,629
Contract liabilities	$ 13,284	$ 8,132

Revenues and Accounts Receiva_4

Revenues and Accounts Receivable - Additional Information (Details)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2024 USD ($) Customer	Jun. 30, 2023 Customer	Jun. 30, 2024 USD ($) Customer	Jun. 30, 2023 Customer	Dec. 31, 2023 USD ($) Customer
Accounts Notes And Loans Receivable [Line Items]
Contracts assets acquired through business acquisitions			$ 2,400,000		$ 2,200,000
Contract liabilities acquired through business acquisitions			0		0
Revenue remaining performance obligations	$ 80,500,000		80,500,000		$ 81,900,000
Contract Liabilities
Accounts Notes And Loans Receivable [Line Items]
Contract with customer liabilities, revenue recognized	$ 4,800,000		$ 9,300,000
Customer Concentration Risk | Accounts Receivable | Significant Customer
Accounts Notes And Loans Receivable [Line Items]
Concentration risk percentage			10%		10%
Number of customers | Customer			1		0
Customer Concentration Risk | Revenue | Significant Customer
Accounts Notes And Loans Receivable [Line Items]
Concentration risk percentage	10%	12.30%	10%	10.40%
Number of customers | Customer	0	1	0	1

Revenues and Accounts Receiva_5

Revenues and Accounts Receivable - Additional Information (Details1) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue remaining performance obligations	$ 80.5	$ 81.9
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2024-07-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue remaining performance obligations	$ 60.5
Revenue remaining performance obligations, satisfaction period	6 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2025-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue remaining performance obligations	$ 20
Revenue remaining performance obligations, satisfaction period	1 year

Revenues and Accounts Receiva_6

Revenues and Accounts Receivable - Schedule of Accounts Receivable, Net (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023	Dec. 31, 2022
Revenues And Accounts Receivable [Abstract]
Accounts receivable, invoiced	$ 136,972	$ 115,064
Accounts receivable, other	1,481	20
Allowance for doubtful accounts	(2,784)	(2,724)	$ (1,915)
Accounts receivable, net	$ 135,669	$ 112,360

Revenues and Accounts Receiva_7

Revenues and Accounts Receivable - Schedule of Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands		6 Months Ended	12 Months Ended
		Jun. 30, 2024	Dec. 31, 2023
Revenues And Accounts Receivable [Abstract]
Beginning Balance		$ 2,724	$ 1,915
Bad Debt Expense (Recovery)		(659)	3,142
Charged to Allowance		(11)	(2,333)
Other	[1]	730
Ending Balance		$ 2,784	$ 2,724
[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	Jun. 30, 2024	Dec. 31, 2023
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Deposits	$ 1,412	$ 1,764
Prepaid expenses	9,831	8,112
Supplies	2,979	3,819
Prepaid and other current assets	$ 14,222	$ 13,695

Property and Equipment, Net - P

Property and Equipment, Net - Property and Equipment, Net (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 115,446	$ 108,592
Less: Accumulated depreciation	(63,405)	(56,812)
Total property and equipment— net	63,627	56,825
Lab and test equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	20,989	20,341
Vehicles
Property Plant And Equipment [Line Items]
Property and equipment, gross	6,096	6,033
Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	54,782	50,387
Furniture and fixtures
Property Plant And Equipment [Line Items]
Property and equipment, gross	3,001	2,963
Leasehold improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	12,444	10,808
Aircraft
Property Plant And Equipment [Line Items]
Property and equipment, gross	12,386	12,312
Building
Property Plant And Equipment [Line Items]
Property and equipment, gross	5,748	5,748
Land
Property Plant And Equipment [Line Items]
Property and equipment, gross	1,089	1,089
Construction in Progress
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 10,497	$ 3,956

Property and Equipment, Net - A

Property and Equipment, Net - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Property Plant And Equipment [Line Items]
Depreciation expense	$ 4.1	$ 2.6	$ 7	$ 4.8

Leases - Additional Information

Leases - Additional Information (Details)	6 Months Ended
	Jun. 30, 2024
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		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Lessee Lease Description [Line Items]
Total operating lease cost	$ 3,536	$ 3,103	$ 6,986	$ 6,170
Total finance lease cost	1,497	1,600	2,970	2,884
Total lease cost	5,033	4,703	9,956	9,054
Selling, General and Administrative Expenses
Lessee Lease Description [Line Items]
Lease cost	2,956	2,804	5,950	5,545
Variable lease cost	580	299	1,036	625
Depreciation and Amortization
Lessee Lease Description [Line Items]
Amortization of right of use assets	1,293	1,429	2,571	2,583
Interest Expense, Net
Lessee Lease Description [Line Items]
Interest on lease liabilities	$ 204	$ 171	$ 399	$ 301

Leases - Summary of Supplementa

Leases - Summary of Supplemental Cash Flow Information Related To Leases (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023
Leases [Abstract]
Operating cash flows used in operating leases	$ 6,170	$ 5,306
Operating cash flows used in finance leases	399	301
Financing cash flows used in finance leases	3,103	2,198
Operating leases	9,694	23,831
Finance leases	$ 2,666	$ 3,326

Leases - Summary of Weighted Av

Leases - Summary of Weighted Average Remaining Lease Terms and Weighted Average Discount Rates (Details)	Jun. 30, 2024	Jun. 30, 2023
Leases [Abstract]
Weighted average remaining lease term, Operating Leases	5 years 6 months	4 years 4 months 24 days
Weighted average remaining lease term, Finance Leases	3 years 3 months 18 days	3 years 4 months 24 days
Weighted average discount rate, Operating Leases	2.80%	4.40%
Weighted average discount rate, Finance Leases	5.80%	6.50%

Leases - Summary of Maturities

Leases - Summary of Maturities of Lease Liabilities (Details) $ in Thousands	Jun. 30, 2024 USD ($)
Leases [Abstract]
Operating Leases, Remainder of 2024	$ 6,623
Operating Leases, 2025	11,643
Operating Leases, 2026	9,342
Operating Leases, 2027	6,484
Operating Leases, 2028	5,029
Operating Leases, 2029 and thereafter	6,362
Operating Leases, Total undiscounted future minimum lease payments	45,483
Operating Leases, Less imputed interest	(4,347)
Operating Leases, Total discounted future minimum lease payments	41,136
Finance Leases, Remainder of 2024	2,547
Finance Leases, 2025	4,072
Finance Leases, 2026	3,409
Finance Leases, 2027	2,408
Finance Leases, 2028	1,244
Finance Leases, 2029 and thereafter	0
Finance Leases, Total undiscounted future minimum lease payments	13,680
Finance Leases, Less imputed interest	(1,452)
Finance Leases, Total discounted future minimum lease payments	$ 12,228

Business Acquisitions - Additio

Business Acquisitions - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	May 31, 2024	Feb. 28, 2024	Jan. 31, 2024
Business Acquisition [Line Items]
Transaction costs related to business combinations	$ 1,082	$ 2,696	$ 3,607	$ 3,471
Common Stock			9,271
Business combination, paid in cash			71,889
Acquisitions measurement period adjustments			40,900
EPIC
Business Acquisition [Line Items]
Percentage of interests acquired							100%
Common Stock			4,748
Business combination, paid in cash			19,914
2DOT
Business Acquisition [Line Items]
Percentage of interests acquired						100%
Common Stock			1,832
Business combination, paid in cash			39,393
Paragon
Business Acquisition [Line Items]
Percentage of interests acquired					100%
Common Stock			2,691
Business combination, paid in cash			10,982
EPIC, Two Dot
Business Acquisition [Line Items]
Revenue	7,700	10,600	11,600	11,600
Pre-tax income (loss)	1,100	$ 800	2,400	$ 1,000
EnvStd and IAG | 2026 Earn Out
Business Acquisition [Line Items]
Payment through cash or common stock			13,100
Common Stock			13,100
Business combination, earn-out payment, maximum	$ 40,400		40,400
Business combination, paid in cash			$ 14,200

Business Acquisitions - Summary

Business Acquisitions - Summary of Elements of Preliminary Purchase Price of Acquisitions (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2024 USD ($)
Business Acquisition [Line Items]
Cash	$ 71,889
Common Stock	9,271
Other Purchase Price Components	(432)
Contingent Consideration	11,113
Total Purchase Price	91,841
EPIC
Business Acquisition [Line Items]
Cash	19,914
Common Stock	4,748
Other Purchase Price Components	587
Contingent Consideration	11,113
Total Purchase Price	36,362
2DOT
Business Acquisition [Line Items]
Cash	39,393
Common Stock	1,832
Other Purchase Price Components	(1,179)
Contingent Consideration	0
Total Purchase Price	40,046
ETA
Business Acquisition [Line Items]
Cash	1,600
Other Purchase Price Components	400
Total Purchase Price	2,000
Paragon
Business Acquisition [Line Items]
Cash	10,982
Common Stock	2,691
Other Purchase Price Components	(240)
Total Purchase Price	$ 13,433

Business Acquisitions - Summa_2

Business Acquisitions - Summary of Purchase Price Attributable to Acquisitions (Details) $ in Thousands	Jun. 30, 2024 USD ($)	[1]
Business Acquisition [Line Items]
Cash	$ 1,639
Accounts receivable and contract assets	5,724
Other current assets	222
Current assets	7,585
Property and equipment	373
Operating lease right-of-use-asset	2,100
Goodwill	72,793
Total assets	97,195
Current liabilities	3,626
Operating lease liability - net of current portion	1,706
Other non-current liabilities	22
Total liabilities	5,354
Purchase price	91,841
EPIC
Business Acquisition [Line Items]
Cash	1,045
Accounts receivable and contract assets	1,772
Other current assets	78
Current assets	2,895
Property and equipment	43
Operating lease right-of-use-asset	1
Goodwill	20,842
Total assets	38,125
Current liabilities	1,763
Total liabilities	1,763
Purchase price	36,362
2DOT
Business Acquisition [Line Items]
Cash	143
Accounts receivable and contract assets	740
Other current assets	59
Current assets	942
Operating lease right-of-use-asset	301
Goodwill	39,388
Total assets	40,631
Current liabilities	392
Operating lease liability - net of current portion	193
Total liabilities	585
Purchase price	40,046
ETA
Business Acquisition [Line Items]
Goodwill	2,000
Total assets	2,000
Purchase price	2,000
Paragon
Business Acquisition [Line Items]
Cash	451
Accounts receivable and contract assets	3,212
Other current assets	85
Current assets	3,748
Property and equipment	330
Operating lease right-of-use-asset	1,798
Goodwill	10,563
Total assets	16,439
Current liabilities	1,471
Operating lease liability - net of current portion	1,513
Other non-current liabilities	22
Total liabilities	3,006
Purchase price	13,433
Customer Relationships
Business Acquisition [Line Items]
Intangible assets	12,327
Customer Relationships | EPIC
Business Acquisition [Line Items]
Intangible assets	12,327
Trade Names
Business Acquisition [Line Items]
Intangible assets	652
Trade Names | EPIC
Business Acquisition [Line Items]
Intangible assets	652
Covenants Not to Compete
Business Acquisition [Line Items]
Intangible assets	1,365
Covenants Not to Compete | EPIC
Business Acquisition [Line Items]
Intangible assets	$ 1,365
[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		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Business Acquisition [Line Items]
Revenues	$ 173,325	$ 159,101	$ 328,650	$ 290,529
Net (loss) income	(10,170)	(7,174)	(23,527)	(21,893)
Acquisition Proforma
Business Acquisition [Line Items]
Revenues	2,536	18,177	7,396	43,808
Net (loss) income	436	1,960	1,362	3,703
Consolidated Proforma
Business Acquisition [Line Items]
Revenues	175,861	177,278	336,046	334,337
Net (loss) income	$ (9,734)	$ (5,214)	$ (22,165)	$ (18,190)

Goodwill and Intangible Asset_2

Goodwill and Intangible Assets - Schedule of Amounts Related to Goodwill (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2024 USD ($)
Goodwill [Line Items]
Beginning balance	$ 364,449
Goodwill acquired during the period	111,813
Acquisitions measurement period adjustments	(39,020)
Prior year acquisitions measurement period adjustments	(1,857)
Foreign currency translation impact	98
Ending balance	435,483
Assessment, Permitting and Response
Goodwill [Line Items]
Beginning balance	184,946
Goodwill acquired during the period	2,000
Ending balance	186,946
Measurement and Analysis
Goodwill [Line Items]
Beginning balance	93,890
Prior year acquisitions measurement period adjustments	(844)
Ending balance	93,046
Remediation and Reuse Segment
Goodwill [Line Items]
Beginning balance	85,613
Goodwill acquired during the period	109,813
Acquisitions measurement period adjustments	(39,020)
Prior year acquisitions measurement period adjustments	(1,013)
Foreign currency translation impact	98
Ending balance	$ 155,491

Goodwill and Intangible Asset_3

Goodwill and Intangible Assets - Schedule of Amounts Related to Finite-Lived Intangible Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Finite-Lived Intangible Assets [Line Items]
Gross Balance	$ 349,260	$ 332,635
Accumulated Amortization	206,390	191,822
Total Intangible Assets—Net	142,870	140,813
Customer Relationships
Finite-Lived Intangible Assets [Line Items]
Gross Balance	241,298	227,986
Accumulated Amortization	127,105	116,226
Total Intangible Assets—Net	114,193	111,760
Covenants Not to Compete
Finite-Lived Intangible Assets [Line Items]
Gross Balance	37,809	36,250
Accumulated Amortization	32,177	30,889
Total Intangible Assets—Net	5,632	5,361
Trade Names
Finite-Lived Intangible Assets [Line Items]
Gross Balance	25,106	24,434
Accumulated Amortization	22,030	20,720
Total Intangible Assets—Net	3,076	3,714
Proprietary Software
Finite-Lived Intangible Assets [Line Items]
Gross Balance	27,568	26,486
Accumulated Amortization	20,117	19,309
Total Intangible Assets—Net	7,451	7,177
Patent
Finite-Lived Intangible Assets [Line Items]
Gross Balance	17,479	17,479
Accumulated Amortization	4,961	4,678
Total Intangible Assets—Net	$ 12,518	$ 12,801

Goodwill and Intangible Asset_4

Goodwill and Intangible Assets - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization expense	$ 7.1	$ 7.4	$ 14.6	$ 14.6

Goodwill and Intangible Asset_5

Goodwill and Intangible Assets - Schedule of Future Amortization Expense (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Goodwill and Intangible Assets Disclosure [Abstract]
2024 (remaining)	$ 15,430
2025	23,024
2026	18,038
2027	17,201
2028	14,349
Thereafter	54,828
Total Intangible Assets—Net	$ 142,870	$ 140,813

Accounts Payable and Other Ac_3

Accounts Payable and Other Accrued Liabilities - Summary of Accounts Payable and Other Accrued Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Payables and Accruals [Abstract]
Accounts payable	$ 24,294	$ 31,053
Accrued expenses	14,018	16,059
Other business acquisitions purchase price obligations	2,663	1,022
Contract liabilities	13,284	8,132
Other current liabilities	3,964	3,654
Total accounts payable and other accrued liabilities	$ 58,223	$ 59,920

Accrued Payroll and Benefits -

Accrued Payroll and Benefits - Schedule of Accrued Payroll and Benefits (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Statement of Financial Position [Abstract]
Accrued bonuses	$ 7,496	$ 18,453
Accrued paid time off	5,092	1,316
Accrued payroll	11,908	11,814
Accrued other	3,843	3,077
Total accrued payroll and benefits	$ 28,339	$ 34,660

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Income Tax Disclosure [Abstract]
Annual effective tax rate ("ETR") from continuing operations	(45.30%)	(2.20%)	(16.80%)	(7.50%)
Income tax (benefit) expense	$ 2,619,000	$ 151,000	$ 3,112,000	$ 1,518,000
Federal statutory rate			21%
Uncertain tax positions	$ 0		$ 0

Debt - Schedule of Debt (Detail

Debt - Schedule of Debt (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Line Of Credit Facility [Line Items]
Less deferred debt issuance costs	$ (1,368)	$ (1,379)
Total debt	212,416	163,184
Less current portion of long-term debt	(23,667)	(14,196)
Long-term debt, less current portion	188,749	148,988
Term Loan Facility
Line Of Credit Facility [Line Items]
Total debt	200,314	154,219
Revolving Line of Credit
Line Of Credit Facility [Line Items]
Total debt	3,651
Aircraft Loan
Line Of Credit Facility [Line Items]
Total debt	$ 9,819	$ 10,344

Debt - Additional Information (

Debt - Additional Information (Details) - USD ($)					3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 05, 2024	May 30, 2023	May 18, 2023	Apr. 27, 2021	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023	May 31, 2024	Jan. 31, 2024
Line Of Credit Facility [Line Items]
Gross of deferred debt issuance cost					$ 1,368,000		$ 1,368,000		$ 1,379,000
Interest Rate Swap
Line Of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	$ 100,000,000
Second Interest Rate Swap
Line Of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	$ 80,000,000
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		1.319%
Floating Component | Second Interest Rate Swap
Line Of Credit Facility [Line Items]
Credit facility maturity date		Apr. 27, 2026
Line of credit facility, additional borrowings		$ 70,000,000
Interest rate		3.88%
LIBOR | Interest Rate Swap
Line Of Credit Facility [Line Items]
Interest rate		1.39%
SOFR
Line Of Credit Facility [Line Items]
Interest rate	3.27%
2021 Credit Facility Term Loan
Line Of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity				$ 300,000,000							$ 100,000,000
Credit facility maturity date				Apr. 27, 2026
Leverage Capacity, Description							increasing its leverage capacity from 3.75 times to 4.25 times for four quarters beginning with the first quarter of 2024
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							240%		190%
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					7.40%	6.30%	7.40%	6.30%
2021 Credit Facility Term Loan | Interest Rate Swap
Line Of Credit Facility [Line Items]
Weighted average interest rate					3.40%	2.10%	3.40%	2.10%
2021 Credit Facility Term Loan | SOFR
Line Of Credit Facility [Line Items]
Interest rate							0.10%
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										$ 15,000,000
Credit facility maturity date							Apr. 15, 2025
Loan and Aircraft Security Agreement
Line Of Credit Facility [Line Items]
Debt instrument face amount			$ 10,900,000
Percentage of prepayment fee for year one			3%
Percentage of prepayment fee for year two			2%
Percentage of prepayment fee for year three			1%
Loan and Aircraft Security Agreement | SOFR
Line Of Credit Facility [Line Items]
Interest rate			1.86%
Term Loan Facility | 2021 Credit Facility Term Loan
Line Of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity				175,000,000							50,000,000
Installment repayment amount					$ 600,000	$ 2,200,000	$ 3,900,000	$ 4,400,000
Repayments of Debt							$ 3,300,000
Revolving Line of Credit | 2021 Credit Facility Term Loan
Line Of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity				125,000,000							$ 50,000,000
Revolving Line of Credit | Letter of Credit | 2021 Credit Facility Term Loan
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	6 Months Ended
	Jun. 30, 2024
Term Loan Facility
Subsequent Event [Line Items]
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
Additional Term Loan
Subsequent Event [Line Items]
Debt instrument, quarterly installment rate, June 30, 2024	1.25%
Debt instrument, quarterly installment rate, September 30, 2024	1.25%
Debt instrument, quarterly installment rate, December 31, 2024	1.25%
Debt instrument, quarterly installment rate, March 31, 2025	1.25%
Debt instrument, quarterly installment rate, June 30, 2025	1.25%
Debt instrument, quarterly installment rate, September 30, 2025	1.25%
Debt instrument, quarterly installment rate, December 31, 2025	1.25%
Debt instrument, quarterly installment rate, March 31, 2026	1.88%
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 SOFR (Details)			6 Months Ended
	Jun. 05, 2024	Apr. 27, 2021	Jun. 30, 2024
SOFR
Subsequent Event [Line Items]
Interest rate	3.27%
2021 Credit Facility Term Loan | SOFR
Subsequent Event [Line Items]
Interest rate			0.10%
2021 Credit Facility Term Loan | Pricing Tier1
Subsequent Event [Line Items]
Commitment Fee		0.25%
Letter of Credit Fee		2.50%
2021 Credit Facility Term Loan | Pricing Tier1 | Minimum
Subsequent Event [Line Items]
Net Leverage Ratio		375%
2021 Credit Facility Term Loan | Pricing Tier1 | Base Rate Plus
Subsequent Event [Line Items]
Interest rate		1.50%
2021 Credit Facility Term Loan | Pricing Tier1 | SOFR
Subsequent Event [Line Items]
Interest rate		2.50%
2021 Credit Facility Term Loan | Pricing Tier2
Subsequent Event [Line Items]
Commitment Fee		0.23%
Letter of Credit Fee		2.25%
2021 Credit Facility Term Loan | Pricing Tier2 | Maximum
Subsequent Event [Line Items]
Net Leverage Ratio		375%
2021 Credit Facility Term Loan | Pricing Tier2 | Minimum
Subsequent Event [Line Items]
Net Leverage Ratio		325%
2021 Credit Facility Term Loan | Pricing Tier2 | Base Rate Plus
Subsequent Event [Line Items]
Interest rate		1.25%
2021 Credit Facility Term Loan | Pricing Tier2 | SOFR
Subsequent Event [Line Items]
Interest rate		2.25%
2021 Credit Facility Term Loan | Pricing Tier3
Subsequent Event [Line Items]
Commitment Fee		0.20%
Letter of Credit Fee		2%
2021 Credit Facility Term Loan | Pricing Tier3 | Maximum
Subsequent Event [Line Items]
Net Leverage Ratio		325%
2021 Credit Facility Term Loan | Pricing Tier3 | Minimum
Subsequent Event [Line Items]
Net Leverage Ratio		250%
2021 Credit Facility Term Loan | Pricing Tier3 | Base Rate Plus
Subsequent Event [Line Items]
Interest rate		1%
2021 Credit Facility Term Loan | Pricing Tier3 | SOFR
Subsequent Event [Line Items]
Interest rate		2%
2021 Credit Facility Term Loan | Pricing Tier4
Subsequent Event [Line Items]
Commitment Fee		0.15%
Letter of Credit Fee		1.75%
2021 Credit Facility Term Loan | Pricing Tier4 | Maximum
Subsequent Event [Line Items]
Net Leverage Ratio		250%
2021 Credit Facility Term Loan | Pricing Tier4 | Minimum
Subsequent Event [Line Items]
Net Leverage Ratio		175%
2021 Credit Facility Term Loan | Pricing Tier4 | Base Rate Plus
Subsequent Event [Line Items]
Interest rate		0.75%
2021 Credit Facility Term Loan | Pricing Tier4 | SOFR
Subsequent Event [Line Items]
Interest rate		1.75%
2021 Credit Facility Term Loan | Pricing Tier5
Subsequent Event [Line Items]
Commitment Fee		0.15%
Letter of Credit Fee		1.50%
2021 Credit Facility Term Loan | Pricing Tier5 | Maximum
Subsequent Event [Line Items]
Net Leverage Ratio		175%
2021 Credit Facility Term Loan | Pricing Tier5 | Base Rate Plus
Subsequent Event [Line Items]
Interest rate		0.50%
2021 Credit Facility Term Loan | Pricing Tier5 | SOFR
Subsequent Event [Line Items]
Interest rate		1.50%

Debt - Schedule of Aggregate An

Debt - Schedule of Aggregate Annual Maturities of Long-Term Debt (Details) $ in Thousands	Jun. 30, 2024 USD ($)
Line of Credit Facility [Line Items]
2025	$ 23,667
2026	182,595
2027	1,273
2028	6,249
Total	213,784
2021 Credit Facility Revolver
Line of Credit Facility [Line Items]
2025	3,651
Total	3,651
2021 Credit Facility Term Loan
Line of Credit Facility [Line Items]
2025	18,907
2026	181,407
Total	200,314
Aircraft Loan
Line of Credit Facility [Line Items]
2025	1,109
2026	1,188
2027	1,273
2028	6,249
Total	$ 9,819

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	Jun. 30, 2024		Dec. 31, 2023		Jun. 30, 2023	Dec. 31, 2022
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Level 3 Liabilities	$ 35,516		$ 25,057		$ 33,585	$ 33,986
Level 3 Assets	3,108		3,461		6,462	6,046
Business Acquisitions Contingent Consideration, Current
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Level 3 Liabilities	6,351		3,592		4,119	3,801
Business Acquisitions Contingent Consideration, Long-Term
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Level 3 Liabilities	9,595		2,448		2,311	4,454
Conversion Option
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Level 3 Liabilities	19,570		19,017		27,155	25,731
Interest Rate Swap
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Level 3 Assets	$ 3,108	[1]	$ 3,461	[1]	$ 6,462	$ 6,046
[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	6 Months Ended
	Jun. 30, 2024		Jun. 30, 2023
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Beginning balance	$ 25,057		$ 33,986
Total Assets, Beginning balance	3,461		6,046
Acquisitions	11,113		25
Asset value, Changes in fair value included in earnings	$ (353)		$ 416
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Fair value changes in business acquisition contingencies		Fair value changes in business acquisition contingencies
Changes in fair value included in earnings	$ 796		$ 1,379
Fair Value, Liability, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Fair value changes in business acquisition contingencies		Fair value changes in business acquisition contingencies
Payment of contingent consideration payable	$ (1,450)		$ (1,805)
Ending balance	35,516		33,585
Total Assets, Ending balance	3,108		6,462
Business Acquisitions Contingent Consideration, Current
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Beginning balance	3,592		3,801
Acquisitions	4,976		25
Changes in fair value included in earnings	59		(162)
Payment of contingent consideration payable	(1,450)		(1,805)
Reclass of long term to short term contingent liabilities	(826)		2,260
Ending balance	6,351		4,119
Business Acquisitions Contingent Consideration, Long-Term
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Beginning balance	2,448		4,454
Acquisitions	6,137
Changes in fair value included in earnings	184		117
Reclass of long term to short term contingent liabilities	826		(2,260)
Ending balance	9,595		2,311
Conversion Option
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Beginning balance	19,017		25,731
Changes in fair value included in earnings	553		1,424
Ending balance	19,570		27,155
Interest Rate Swap
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Assets, Beginning balance	3,461	[1]	6,046
Asset value, Changes in fair value included in earnings	(353)		416
Total Assets, Ending balance	$ 3,108	[1]	$ 6,462
[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		1 Months Ended	3 Months Ended				6 Months Ended
	Apr. 13, 2020	Jan. 31, 2024	Jun. 30, 2024	Mar. 31, 2024	Jun. 30, 2023	Mar. 31, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023	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			$ 2,750	$ 2,814	$ 4,100	$ 4,100
Number of debt incurrence test ratio							4.5
Convertible And Redeemable Series A-2 Preferred Stock
Temporary Equity [Line Items]
Number of shares issued	17,500		11,667	11,667			11,667		17,500
Par value per share	$ 0.0001		$ 0.0001				$ 0.0001		$ 0.0001
Debt issuance costs, net	$ 1,300
Preferred stock, dividends paid			$ 2,800		$ 4,100		$ 5,600	$ 8,200
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. In January 2024, the Company redeemed $60 million of the outstanding Convertible and Redeemable Series A-2 Preferred Stock with cash. As of June 30, 2024, the aggregate amount of the Convertible and Redeemable Series A-2 Preferred Stock issued and outstanding was $122.2 million, or 11,667 shares.
Aggregate stated value of stock redeemed			25,000				$ 25,000
Redeemed in cash		$ 60,000
Temporary equity, aggregate liquidation preference			$ 122,200	$ 122,200			$ 122,200		$ 182,200
Number of shares outstanding			11,667	11,667	17,500	17,500	11,667	17,500	17,500	17,500
Compound embedded derivative, fair value net			$ 19,600				$ 19,600		$ 19,000
Convertible And Redeemable Series A-2 Preferred Stock | Other Expense
Temporary Equity [Line Items]
Compound embedded derivative, change in net fair value			500		$ 500		600	$ 1,400
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				60,000
Convertible And Redeemable Series A-2 Preferred Stock | Year 5
Temporary Equity [Line Items]
Temporary equity convertible into common stock			60,000				60,000
Convertible And Redeemable Series A-2 Preferred Stock | Year 6
Temporary Equity [Line Items]
Temporary equity convertible into common stock			$ 120,000				$ 120,000

Stockholder's Equity - Addition

Stockholder's Equity - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended			6 Months Ended
	Apr. 22, 2024	Apr. 18, 2024	Jun. 30, 2024	Mar. 31, 2024	Jun. 30, 2023	Jun. 30, 2024
Class of Stock [Line Items]
Net proceeds						$ 121,776
Common Stock
Class of Stock [Line Items]
Common stock issued, shares			3,450,000	427,631	130,115
Common Stock | IPO
Class of Stock [Line Items]
Net proceeds		$ 121,800
Common Stock | Secondary Public Offering
Class of Stock [Line Items]
Common stock issued, shares	3,450,000
Common Stock | Underwriters
Class of Stock [Line Items]
Initial Shares of public offering price	$ 37.15
Discounts and commisions per share	$ 1.67175

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				6 Months Ended
	Jun. 30, 2024	Mar. 31, 2024	Jun. 30, 2023	Mar. 31, 2023	Jun. 30, 2024	Jun. 30, 2023
Earnings Per Share [Abstract]
Net loss	$ (10,170)	$ (13,357)	$ (7,174)	$ (14,719)	$ (23,527)	$ (21,893)
Convertible and redeemable series A-2 preferred stock dividend	(2,750)		(4,100)		(5,564)	(8,200)
Net loss attributable to common stockholders -basic	(12,920)		(11,274)		(29,091)	(30,093)
Net loss attributable to common stockholders -diluted	$ (12,920)		$ (11,274)		$ (29,091)	$ (30,093)
Weighted-average number of shares of common stock outstanding - basic	33,318		30,047		31,850	29,952
Weighted-average number of shares of common stock outstanding - diluted	33,318		30,047		31,850	29,952
Net loss per share attributable to common stockholders - basic	$ (0.39)		$ (0.38)		$ (0.91)	$ (1)
Net loss per share attributable to common stockholders - diluted	$ (0.39)		$ (0.38)		$ (0.91)	$ (1)

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		6 Months Ended
		Jun. 30, 2024	Jun. 30, 2023
Stock Options
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of loss per share amount	[1]	3,179,129	3,436,263
Restricted Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of loss per share amount	[1]	2,579,982	2,325,322
Series A-2 Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of loss per share amount	[1]	3,317,141	5,350,017
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 6,782,913 and 7,578,724 common stock equivalents that are out of the money as of June 30, 2024 and June 30, 2023 , 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	6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023
Earnings Per Share [Abstract]
Number of shares out of money	6,782,913	7,578,724

Stock-Based Plans and Compens_3

Stock-Based Plans and Compensation - Additional Information (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Share Based Compensation Arrangement by Share Based Payment Award [Line Items]
Total unrecognized stock-based compensation expense related to unvested options, restricted stock and stock appreciation rights granted under the Plans	$ 109,600,000	$ 141,500,000	$ 109,600,000	$ 141,500,000
Unrecognized expense expected to be recognized period			2 years 6 months
Stock compensation expenses	11,831,000	11,090,000	$ 23,103,000	24,125,000
2013 Plan
Share Based Compensation Arrangement by Share Based Payment Award [Line Items]
Stock compensation expenses	0	0	0	0
Two Thousand Seventeen Plan | Restricted Stock
Share Based Compensation Arrangement by Share Based Payment Award [Line Items]
Stock compensation expenses	8,399,000	7,264,000	16,318,000	15,961,000
Two Thousand Seventeen Plan | Stock Options
Share Based Compensation Arrangement by Share Based Payment Award [Line Items]
Stock compensation expenses	1,142,000	1,536,000	$ 2,205,000	3,609,000
Two Thousand Seventeen Plan | Stock Appreciation Rights (SARs)
Share Based Compensation Arrangement by Share Based Payment Award [Line Items]
Shares of vested over period			5 years
Stock compensation expenses	$ 2,290,000	$ 2,290,000	$ 4,580,000	$ 4,555,000
Shares, granted			3,000,000
Exercise price	$ 66.79		$ 66.79
Remaining contractual terms			10 years
Fair value vested in period			$ 46,000,000
Weighted average remaining contract life			7 years 5 months 15 days

Stock-Based Plans and Compens_4

Stock-Based Plans and Compensation - Summary of Number of Shares Authorized to be Issued and Available for Grant (Details) - shares		Jun. 30, 2024		Jan. 31, 2024	Jun. 30, 2023		Jan. 31, 2023
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares authorized to be issued		9,574,495			8,366,932
Shares available for grant	[1]	1,677,508			750,326
2017 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares authorized to be issued		7,538,276			6,330,588
Shares available for grant		1,677,508	[1]	1,207,563	750,326	[1]	1,189,801
2013 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares authorized to be issued		2,036,219			2,036,344
[1] In January 2024 and January 2023 the Board of Directors ratified the addition of 1,207,563 and 1,189,801 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.

Stock-Based Plans and Compens_5

Stock-Based Plans and Compensation - Summary of Number of Shares Authorized to be Issued and Available for Grant (Parenthetical) (Details) - shares		Jun. 30, 2024		Jan. 31, 2024	Jun. 30, 2023		Jan. 31, 2023
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares available for grant	[1]	1,677,508			750,326
2017 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares available for grant		1,677,508	[1]	1,207,563	750,326	[1]	1,189,801
[1] In January 2024 and January 2023 the Board of Directors ratified the addition of 1,207,563 and 1,189,801 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.

Stock-Based Plans and Compens_6

Stock-Based Plans and Compensation - Schedule of Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock compensation expenses	$ 11,831	$ 11,090	$ 23,103	$ 24,125
2017 Plan | Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock compensation expenses	1,142	1,536	2,205	3,609
2017 Plan | Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock compensation expenses	8,399	7,264	16,318	15,961
2017 Plan | Stock Appreciation Rights (SARs)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock compensation expenses	2,290	2,290	4,580	4,555
Cost of Revenue
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock compensation expenses	1,200	709	2,111	1,601
Cost of Revenue | 2017 Plan | Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock compensation expenses	355	466	629	815
Cost of Revenue | 2017 Plan | Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock compensation expenses	845	243	1,482	786
Selling, General and Administrative Expenses
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock compensation expenses	10,631	10,381	20,992	22,524
Selling, General and Administrative Expenses | 2017 Plan | Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock compensation expenses	787	1,070	1,576	2,794
Selling, General and Administrative Expenses | 2017 Plan | Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock compensation expenses	7,554	7,021	14,836	15,175
Selling, General and Administrative Expenses | 2017 Plan | Stock Appreciation Rights (SARs)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock compensation expenses	$ 2,290	$ 2,290	$ 4,580	$ 4,555

Stock-Based Plans and Compens_7

Stock-Based Plans and Compensation - Schedule of Restricted Stock Activity (Details) - Montrose 2017 Stock Incentive Plan - $ / shares	6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted Average Grant Date Fair Value per Share Outstanding Beginning Balance	$ 15.95	$ 15
Weighted Average Grant Date Fair Value per Share Granted		13.9
Weighted Average Grant Date Fair Value per Share Outstanding Ending Balance	$ 16.27	$ 15.62
Restricted stock units awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding, Shares, Beginning Balance	2,468,722	1,777,715
Granted, Shares	289,155	641,282
Forfeited/cancelled, Shares	(27,953)	(3,559)
Vested, Shares	(149,942)	(90,116)
Outstanding, Shares, Ending Balance	2,579,982	2,325,322
Weighted Average Grant Date Fair Value per Share Granted	$ 40.58	$ 37.27
Weighted Average Grant Date Fair Value per Share Forfeited/ cancelled	37.62	32.16
Weighted Average Grant Date Fair Value per Share Vested	$ 37.49	$ 36.81

Stock-Based Plans and Compens_8

Stock-Based Plans and Compensation - Summary of Performance Hurdles (Details)	6 Months Ended
	Jun. 30, 2024 $ / 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%

Stock-Based Plans and Compens_9

Stock-Based Plans and Compensation - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023	Dec. 31, 2022
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	2,516,272	2,579,566	2,579,566
Options to Purchase Common Stock Granted		233,955
Options to Purchase Common Stock Forfeited/cancelled	(48,765)	(63,085)
Options to Purchase Common Stock Expired	(19,720)	(1,200)
Options to Purchase Common Stock Exercised	(47,948)	(125,229)
Options to Purchase Common Stock Outstanding Ending Balance	2,399,839	2,624,007	2,516,272	2,579,566
Options to Purchase Common Stock Exercisable	1,484,676
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	$ 30.92	$ 31	$ 31
Weighted-Average Exercise Price per Share Granted		32.16
Weighted-Average Exercise Price per Share Forfeited/cancelled	38.87	37.41
Weighted-Average Exercise Price per Share Expired	45.55	25.05
Weighted-Average Exercise Price per Share Exercised	27.05	23.76
Weighted-Average Exercise Price per Share Outstanding Ending Balance	30.72	30.88	30.92	$ 31
Weighted-Average Exercise Price per Share Exercisable	31.13
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	15.95	15	15
Weighted Average Grant Date Fair Value per Share Granted		13.9
Weighted Average Grant Date Fair Value per Share Outstanding Ending Balance	$ 16.27	$ 15.62	$ 15.95	$ 15
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted Average Remaining Contract Life (in Years) Outstanding	7 years	7 years 6 months	7 years	7 years 9 months 18 days
Weighted Average Remaining Contract Life (in Years) Exercisable	6 years 2 months 12 days
Aggregate Intrinsic Value of In-The-Money Options Outstanding	$ 14,488	$ 32,414	$ 13,825	$ 37,292
Aggregate Intrinsic Value of In-The-Money Options Exercised	663	$ 2,794
Aggregate Intrinsic Value of In-The-Money Options Exercisable	$ 20,723
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	792,191	855,695	855,695
Options to Purchase Common Stock Expired		(675)
Options to Purchase Common Stock Exercised	(12,901)	(42,764)
Options to Purchase Common Stock Outstanding Ending Balance	779,290	812,256	792,191	855,695
Options to Purchase Common Stock Exercisable	779,290
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	$ 6.40	$ 6	$ 6
Weighted-Average Exercise Price per Share Expired		6.03
Weighted-Average Exercise Price per Share Exercised	6.08	7.47
Weighted-Average Exercise Price per Share Outstanding Ending Balance	6.41	6.38	6.40	$ 6
Weighted-Average Exercise Price per Share Exercisable	6.41
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	2.16	2	2
Weighted Average Grant Date Fair Value per Share Outstanding Ending Balance	$ 2.20	$ 2.11	$ 2.16	$ 2
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted Average Remaining Contract Life (in Years) Outstanding	1 year 10 months 24 days	2 years 9 months 18 days	2 years 4 months 24 days	3 years 3 months 18 days
Weighted Average Remaining Contract Life (in Years) Exercisable	1 year 10 months 24 days
Aggregate Intrinsic Value of In-The-Money Options Outstanding	$ 29,730	$ 29,030	$ 20,380	$ 32,478
Aggregate Intrinsic Value of In-The-Money Options Exercised		$ 1,514
Aggregate Intrinsic Value of In-The-Money Options Exercisable	$ 29,730

Stock-Based Plans and Compen_10

Stock-Based Plans and Compensation - Summary of Weighted Average Assumptions Used in Black-Sholes Option-pricing Model (Details)	6 Months Ended
	Jun. 30, 2023 $ / shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock value (per share)	$ 32.16
Expected volatility	33.79%
Risk-free interest rate	3.72%
Expected life (years)	7 years
Forfeiture rate	0%
Dividend rate	0%

Stock-Based Plans and Compen_11

Stock-Based Plans and Compensation - Schedule of Common Stock Reserved for Future Issuance (Details) - shares	Jun. 30, 2024		Jan. 31, 2024	Jun. 30, 2023		Jan. 31, 2023
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	10,436,619			9,511,911
Montrose 2013 Stock Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	779,290			812,256
Montrose 2017 Stock Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	9,657,329	[1]	1,207,563	8,699,655	[1]	1,189,801
[1] In January 2024 and 2023, the Board of Directors ratified the addition of 1,207,563 and 1,189,801 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. 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.

Stock-Based Plans and Compen_12

Stock-Based Plans and Compensation - Schedule of Common Stock Reserved for Future Issuance (Parenthetical) (Details) - shares	1 Months Ended
	Jan. 31, 2021	Jun. 30, 2024		Jan. 31, 2024	Jun. 30, 2023		Jan. 31, 2023	Jan. 31, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance		10,436,619			9,511,911
Montrose 2017 Stock Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance		9,657,329	[1]	1,207,563	8,699,655	[1]	1,189,801
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 2024 and 2023, the Board of Directors ratified the addition of 1,207,563 and 1,189,801 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. 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.

Segment Information - Additiona

Segment Information - Additional Information (Details) $ in Millions		6 Months Ended
	Dec. 29, 2023 USD ($)	Jun. 30, 2024 USD ($) Segment	Dec. 31, 2023 USD ($)
Segment Reporting Information [Line Items]
Number of operating segments | Segment		3
Number of reportable segments | Segment		3
Discontinuing Specialty Lab
Segment Reporting Information [Line Items]
Sales price of assets	$ 4.8
Cash received	0.5
Promissory note receivable	$ 4.3
Promissory note receivable, Annual interest rate	9%
Promissory note receivable, net of expected losses and payment		$ 2.1	$ 2.1

Segment Information - Component

Segment Information - Components of Segment Revenues and Adjusted EBITDA (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Segment Reporting Information [Line Items]
Segment Revenues	$ 173,325	$ 159,101	$ 328,650	$ 290,529
Segment Adjusted EBITDA	23,316	21,191	40,238	37,794
Operating Segments
Segment Reporting Information [Line Items]
Segment Revenues	173,325	159,101	328,650	290,529
Segment Adjusted EBITDA	33,909	30,665	61,704	56,596
Assessment, Permitting and Response | Operating Segments
Segment Reporting Information [Line Items]
Segment Revenues	53,444	61,411	112,024	113,625
Segment Adjusted EBITDA	12,621	13,833	28,901	28,099
Measurement and Analysis | Operating Segments
Segment Reporting Information [Line Items]
Segment Revenues	54,812	50,055	100,306	92,582
Segment Adjusted EBITDA	12,359	10,789	18,863	17,176
Remediation and Reuse | Operating Segments
Segment Reporting Information [Line Items]
Segment Revenues	65,069	47,635	116,320	84,322
Segment Adjusted EBITDA	8,929	6,043	13,940	11,321
Corporate and Other
Segment Reporting Information [Line Items]
Segment Adjusted EBITDA	$ (10,593)	$ (9,474)	$ (21,466)	$ (18,802)

Segment Information - Reconcili

Segment Information - Reconciliation of Segment Measure to Net Loss (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024		Jun. 30, 2023
Segment Reporting Information [Line Items]
Adjusted EBITDA		$ 23,316	$ 21,191	$ 40,238		$ 37,794
Interest expense, net		(3,976)	(1,877)	(7,282)		(3,418)
Income tax expense		(2,619)	(151)	(3,112)		(1,518)
Depreciation and amortization		(12,515)	(11,398)	(24,168)		(21,953)
Stock-based compensation		(11,831)	(11,090)	(23,103)		(24,125)
Acquisition costs		(1,082)	(2,696)	(3,607)		(3,471)
Fair value changes in financial instruments		(1,202)	865	(905)		(1,008)
Fair value changes in business acquisition contingencies		(136)	(353)	(242)		45
Expenses related to financing transactions		(95)		(239)		(4)
Discontinued Specialty Lab	[1]		(1,583)	(596)		(4,019)
Other losses or expenses		(30)	(82)	(511)	[2]	(216)
Net loss		$ (10,170)	$ (7,174)	$ (23,527)		$ (21,893)
[1] Amounts consist of operating losses before depreciation related to the Discontinued Specialty Lab. Amount consists of costs associated with a lease abandonment.

Segment Information - Schedule

Segment Information - Schedule of Revenue by Geographic Location (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	$ 173,325	$ 159,101	$ 328,650	$ 290,529
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	137,012	145,162	265,854	271,944
Canada
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	28,597	11,407	49,878	13,283
Other International
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	$ 7,716	$ 2,532	$ 12,918	$ 5,302

Related-Party Transactions - Ad

Related-Party Transactions - Additional Information (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Related Party Transactions [Abstract]
Related party transaction amount	$ 0	$ 0	$ 0	$ 0

Defined Contribution Plan - Add

Defined Contribution Plan - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
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	$ 8.9	$ 1.8	$ 11.6	$ 3.9
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 - Spirit Environmental, LLC. $ in Millions	Jul. 01, 2024 USD ($)
Subsequent Event [Line Items]
Asset acquisition, agreement date	Jul. 01, 2024
Purchase price	$ 17.5
Payment through cash on hand	16
Common Stock
Subsequent Event [Line Items]
Payments through common stock	$ 1.5