Casella Waste Systems (CWST) 10-Q 30 Jul 21 2021 Q2 Quarterly report Financial data

COVER PAGE

COVER PAGE - shares	6 Months Ended
	Jun. 30, 2021	Jul. 15, 2021
Document Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 30, 2021
Document Transition Report	false
Entity File Number	000-23211
Entity Registrant Name	CASELLA WASTE SYSTEMS, INC.
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q2
Current Fiscal Year End Date	--12-31
Entity Central Index Key	0000911177
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	03-0338873
Entity Address, Address Line One	25 Greens Hill Lane,
Entity Address, City or Town	Rutland,
Entity Address, State or Province	VT
Entity Address, Postal Zip Code	05701
City Area Code	802
Local Phone Number	775-0325
Title of 12(b) Security	Class A common stock, $0.01 par value per share
Trading Symbol	CWST
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Amendment Flag	false
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Class A Common Stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		50,398,324
Class B Common Stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		988,200

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
CURRENT ASSETS:
Cash and cash equivalents	$ 167,177	$ 154,342
Accounts receivable, net of allowance for credit losses of $2,238 and $2,333, respectively	78,928	74,198
Refundable income taxes	0	229
Prepaid expenses	13,735	9,289
Inventory	7,994	7,868
Other current assets	1,421	1,328
Total current assets	269,255	247,254
Property, plant and equipment, net of accumulated depreciation and amortization of $936,029 and $900,882, respectively	532,824	510,512
Operating lease right-of-use assets	90,707	95,310
Goodwill	196,686	194,901
Intangible assets, net	55,927	58,324
Restricted assets	1,953	1,848
Cost method investments	11,264	11,264
Deferred income taxes	53,086	61,163
Other non-current assets	16,131	13,322
Total assets	1,227,833	1,193,898
CURRENT LIABILITIES:
Current maturities of debt	14,716	9,240
Current operating lease liabilities	7,207	8,547
Accounts payable	60,064	49,198
Accrued payroll and related expenses	13,612	17,282
Accrued interest	2,045	2,126
Contract liabilities	3,133	2,685
Current accrued capping, closure and post-closure costs	11,118	10,268
Other accrued liabilities	35,663	31,862
Total current liabilities	147,558	131,208
Debt, less current portion	526,830	530,411
Operating lease liabilities, less current portion	59,536	60,979
Accrued capping, closure and post-closure costs, less current portion	74,441	72,265
Deferred income taxes	933	912
Other long-term liabilities	30,043	35,981
COMMITMENTS AND CONTINGENCIES
STOCKHOLDERS' EQUITY:
Additional paid-in capital	645,905	639,247
Accumulated deficit	(250,005)	(266,099)
Accumulated other comprehensive loss, net of tax	(7,922)	(11,517)
Total stockholders' equity	388,492	362,142
Total liabilities and stockholders' equity	1,227,833	1,193,898
Class A Common Stock
STOCKHOLDERS' EQUITY:
Common stock	504	501
Class B Common Stock
STOCKHOLDERS' EQUITY:
Common stock	$ 10	$ 10

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2021USD ($)vote$ / sharesshares	Dec. 31, 2020USD ($)vote$ / sharesshares
Accounts receivable - trade, allowance for credit losses | $	$ 2,238	$ 2,333
Accumulated depreciation and amortization | $	$ 936,029	$ 900,882
Class A Common Stock
Common stock, par value (in dollars per share) | $ / shares	$ 0.01	$ 0.01
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	50,398,000	50,101,000
Common stock, shares outstanding	50,398,000	50,101,000
Class B Common Stock
Common stock, par value (in dollars per share) | $ / shares	$ 0.01	$ 0.01
Common stock, shares authorized	1,000,000	1,000,000
Common stock, shares issued	988,000	988,000
Common stock, shares outstanding	988,000	988,000
Votes per share held | vote	10	10

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Income Statement [Abstract]
Revenues	$ 215,875	$ 188,767	$ 405,406	$ 371,676
Operating expenses:
Cost of operations	138,553	123,462	265,691	251,980
General and administration	29,212	24,874	56,343	49,226
Depreciation and amortization	24,337	22,076	47,019	43,482
Expense from acquisition activities	1,632	352	2,046	1,360
Southbridge Landfill closure charge	195	559	352	1,172
Total operating expenses	193,929	171,323	371,451	347,220
Operating income	21,946	17,444	33,955	24,456
Other expense (income):
Interest income	(66)	(45)	(130)	(96)
Interest expense	5,296	5,511	10,764	11,463
Other income	(510)	(492)	(648)	(449)
Other expense, net	4,720	4,974	9,986	10,918
Income before income taxes	17,226	12,470	23,969	13,538
Provision for income taxes	5,443	357	7,875	466
Net income	$ 11,783	$ 12,113	$ 16,094	$ 13,072
Basic earnings per share attributable to common stockholders:
Weighted average common shares outstanding	51,366	48,348	51,273	48,176
Basic earnings per common share (in dollars per share)	$ 0.23	$ 0.25	$ 0.31	$ 0.27
Diluted earnings per share attributable to common stockholders:
Weighted average common shares outstanding	51,546	48,563	51,466	48,411
Diluted earnings per common share (in dollars per share)	$ 0.23	$ 0.25	$ 0.31	$ 0.27

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Statement of Comprehensive Income [Abstract]
Net income	$ 11,783	$ 12,113	$ 16,094	$ 13,072
Hedging activity:
Interest rate swap settlements	(1,186)	(940)	(2,346)	(1,351)
Interest rate swap amounts reclassified into interest expense	1,202	990	2,347	1,357
Unrealized (loss) gain resulting from changes in fair value of derivative instruments	(336)	(1,619)	4,651	(8,876)
Other comprehensive (loss) income, before tax	(320)	(1,569)	4,652	(8,870)
Income tax (benefit) provision related to items of other comprehensive (loss) income	(85)	0	1,057	(112)
Other comprehensive (loss) income, net of tax	(235)	(1,569)	3,595	(8,758)
Comprehensive income	$ 11,548	$ 10,544	$ 19,689	$ 4,314

CONSOLIDATED STATEMENTS OF STOC

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Unaudited) - USD ($) $ in Thousands	Total	Cumulative effect of new accounting principle	Additional Paid-In Capital	Accumulated Deficit	Accumulated DeficitCumulative effect of new accounting principle	Accumulated other comprehensive loss, net of tax	Class A Common Stock	Class A Common StockCommon Stock	Class B Common Stock	Class B Common StockCommon Stock
Beginning balance at Dec. 31, 2019	$ 122,753	$ (189)	$ 485,332	$ (357,016)	$ (189)	$ (6,041)		$ 468		$ 10
Beginning balance (in shares) at Dec. 31, 2019								46,803,000		988,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuances of Class A common stock	100		95					$ 5
Issuance of Class A common stock (in shares)								517,000
Stock-based compensation	1,562		1,562
Net income (loss)	959			959
Hedging activity	(7,189)					(7,189)
Ending balance at Mar. 31, 2020	117,996		486,989	(356,246)		(13,230)		$ 473		$ 10
Ending balance (in shares) at Mar. 31, 2020								47,320,000		988,000
Beginning balance at Dec. 31, 2019	122,753	$ (189)	485,332	(357,016)	$ (189)	(6,041)		$ 468		$ 10
Beginning balance (in shares) at Dec. 31, 2019								46,803,000		988,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	13,072
Hedging activity	(8,758)
Ending balance at Jun. 30, 2020	130,745		489,193	(344,133)		(14,799)		$ 474		$ 10
Ending balance (in shares) at Jun. 30, 2020							47,382,000	47,382,000	988,000	988,000
Beginning balance at Mar. 31, 2020	117,996		486,989	(356,246)		(13,230)		$ 473		$ 10
Beginning balance (in shares) at Mar. 31, 2020								47,320,000		988,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of Class A common stock - acquisition	0		(1)					$ 1
Issuance of Class A common stock - acquisition (in shares)								36,000
Issuances of Class A common stock	387		387
Issuance of Class A common stock (in shares)								26,000
Stock-based compensation	1,818		1,818
Net income (loss)	12,113			12,113
Hedging activity	(1,569)					(1,569)
Ending balance at Jun. 30, 2020	130,745		489,193	(344,133)		(14,799)		$ 474		$ 10
Ending balance (in shares) at Jun. 30, 2020							47,382,000	47,382,000	988,000	988,000
Beginning balance at Dec. 31, 2020	362,142		639,247	(266,099)		(11,517)		$ 501		$ 10
Beginning balance (in shares) at Dec. 31, 2020							50,101,000	50,101,000	988,000	988,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuances of Class A common stock	112		109					$ 3
Issuance of Class A common stock (in shares)								273,000
Stock-based compensation	2,941		2,941
Net income (loss)	4,311			4,311
Hedging activity	3,830					3,830
Ending balance at Mar. 31, 2021	373,336		642,297	(261,788)		(7,687)		$ 504		$ 10
Ending balance (in shares) at Mar. 31, 2021								50,374,000		988,000
Beginning balance at Dec. 31, 2020	362,142		639,247	(266,099)		(11,517)		$ 501		$ 10
Beginning balance (in shares) at Dec. 31, 2020							50,101,000	50,101,000	988,000	988,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	16,094
Hedging activity	3,595
Ending balance at Jun. 30, 2021	388,492		645,905	(250,005)		(7,922)		$ 504		$ 10
Ending balance (in shares) at Jun. 30, 2021							50,398,000	50,398,000	988,000	988,000
Beginning balance at Mar. 31, 2021	373,336		642,297	(261,788)		(7,687)		$ 504		$ 10
Beginning balance (in shares) at Mar. 31, 2021								50,374,000		988,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuances of Class A common stock	492		492
Issuance of Class A common stock (in shares)								24,000
Stock-based compensation	3,116		3,116
Net income (loss)	11,783			11,783
Hedging activity	(235)					(235)
Ending balance at Jun. 30, 2021	$ 388,492		$ 645,905	$ (250,005)		$ (7,922)		$ 504		$ 10
Ending balance (in shares) at Jun. 30, 2021							50,398,000	50,398,000	988,000	988,000

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Cash Flows from Operating Activities:
Net income	$ 16,094	$ 13,072
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	47,019	43,482
Operating lease right-of-use assets expense	2,826	4,588
Interest accretion on landfill and environmental remediation liabilities	3,962	3,542
Amortization of debt issuance costs	1,144	1,054
Stock-based compensation	6,057	3,380
(Gain) loss on sale of property and equipment	(92)	131
Southbridge Landfill non-cash closure charge	(16)	41
Non-cash expense from acquisition activities	1,022	575
Deferred income taxes	7,041	1,256
Changes in assets and liabilities, net of effects of acquisitions and divestitures:
Accounts receivable	(4,712)	6,448
Landfill operating lease contract expenditures	(1,478)	(1,358)
Accounts payable	10,866	(6,967)
Prepaid expenses, inventories and other assets	(7,192)	(2,309)
Accrued expenses, contract liabilities and other liabilities	(7,109)	(7,910)
Net cash provided by operating activities	79,013	62,493
Cash Flows from Investing Activities:
Acquisitions, net of cash acquired	(5,481)	(20,091)
Additions to property, plant and equipment	(56,069)	(51,570)
Proceeds from sale of property and equipment	403	200
Net cash used in investing activities	(61,147)	(71,461)
Cash Flows from Financing Activities:
Proceeds from debt borrowings	500	91,200
Principal payments on debt	(5,643)	(82,719)
Payments of debt issuance costs	0	(11)
Proceeds from the exercise of share based awards	112	100
Net cash (used in) provided by financing activities	(5,031)	8,570
Net increase (decrease) in cash and cash equivalents	12,835	(398)
Cash and cash equivalents, beginning of period	154,342	3,471
Cash and cash equivalents, end of period	167,177	3,073
Supplemental Disclosure of Cash Flow Information:
Cash interest payments	9,701	10,733
Cash income tax payments	411	187
Non-current assets obtained through long-term financing obligations	5,894	11,859
Right-of-use assets obtained in exchange for operating lease liabilities	1,251	3,142
Landfill
Adjustments to reconcile net income to net cash provided by operating activities:
Operating lease right-of-use assets expense	$ 3,581	$ 3,468

BASIS OF PRESENTATION

BASIS OF PRESENTATION	6 Months Ended
	Jun. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
BASIS OF PRESENTATION	BASIS OF PRESENTATION Casella Waste Systems, Inc. (“Parent”), and its subsidiaries (collectively, “we”, “us” or “our”), is a regional, vertically integrated solid waste services company that provides collection, transfer, disposal, landfill, landfill gas-to-energy, recycling and organics services in the northeastern United States. We market recyclable metals, aluminum, plastics, paper, and corrugated cardboard, which have been processed at our recycling facilities or purchased from third-parties. We manage our solid waste operations on a geographic basis through two regional operating segments, the Eastern and Western regions, each of which provides a full range of solid waste services. We manage our resource-renewal operations through the Resource Solutions operating segment, which includes our larger-scale recycling and commodity brokerage operations along with our organics services and large scale commercial and industrial services. Legal, tax, information technology, human resources, certain finance and accounting and other administrative functions are included in our Corporate Entities segment. The accompanying unaudited consolidated financial statements, which include the accounts of the Parent and our wholly-owned subsidiaries, have been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”) pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”). All significant intercompany accounts and transactions are eliminated in consolidation. Investments in entities in which we do not have a controlling financial interest are accounted for under either the equity method or the cost method of accounting, as appropriate. Our significant accounting policies are more fully discussed in Item 8 of our Annual Report on Form 10-K for the fiscal year ended December 31, 2020 ("fiscal year 2020"), which was filed with the SEC on February 19, 2021. Preparation of our consolidated financial statements in accordance with GAAP requires management to make certain estimates and assumptions. These estimates and assumptions affect the accounting for and recognition and disclosure of assets, liabilities, equity, revenues and expenses. We must make these estimates and assumptions because certain information that we use is dependent on future events, cannot be calculated with a high degree of precision given the available data, or simply cannot be readily calculated. In the opinion of management, these consolidated financial statements include all adjustments, which include normal recurring and nonrecurring adjustments, necessary for a fair presentation of the financial position, results of operations and cash flows for the periods presented. The results for the three and six months ended June 30, 2021 may not be indicative of the results for any other interim period or the entire fiscal year. The consolidated financial statements presented herein should be read in conjunction with our audited consolidated financial statements included in our Annual Report on Form 10-K for fiscal year 2020. Recent Events The global outbreak of the novel coronavirus ("COVID-19") pandemic has caused economic disruption across our geographic footprint and has adversely affected our business. The COVID-19 pandemic negatively impacted our revenues starting at the end of the three months ended March 31, 2020, as many small business and construction collection customers required service level changes and volumes into our landfills declined due to lower economic activity. Demand for services has improved as local economies begin to reopen as allowed by State Governments and our collection and disposal volumes, as well as overall operations, have been less impacted by the effects of the COVID-19 pandemic in the three and six months ended June 30, 2021. The COVID-19 pandemic has negatively impacted and may continue to impact our business in other ways, as we have experienced increased costs as a result of the COVID-19 pandemic, including, but not limited to, higher costs associated with providing a safe working environment for our employees (such as increased costs associated with the protection of our employees, including costs for additional safety equipment, hygiene products and enhanced facility cleaning), employee impacts from illness, supporting a remote administrative workforce, community response measures, the inability of customers to continue to pay for services, and temporary facility closures of our customers. As of the date of this filing, we are unable to determine or predict the full extent of any possible continuing impact that the COVID-19 pandemic will have on our business, results of operations, liquidity and capital resources. Future developments, such as the possibility of continuing spread of COVID-19 across our geographic footprint, the rate of vaccinations, the severity and containment of certain COVID-19 variants along with the pace and extent to which the States in which we operate continue to facilitate a return to normal economic and operation conditions are uncertain and cannot be predicted at this time. Subsequent Events We have evaluated subsequent events or transactions that have occurred after the consolidated balance sheet date of June 30, 2021 through the date of filing of the consolidated financial statements with the SEC on this Quarterly Report on Form 10-Q. We have determined, except as disclosed, that there are no subsequent events that require disclosure in this Quarterly Report on Form 10-Q.

ACCOUNTING CHANGES

ACCOUNTING CHANGES	6 Months Ended
	Jun. 30, 2021
Accounting Changes and Error Corrections [Abstract]
ACCOUNTING CHANGES	ACCOUNTING CHANGES A table providing a brief description of recent Accounting Standards Updates ("ASUs") to the Accounting Standards Codification (“ASC”) issued by the Financial Accounting Standards Board (“FASB”) that we adopted and deemed to have a material impact on our consolidated financial statements, or a possible material impact in the future, based on current account balances and activity follows: Standard Description Effect on the Financial Statements or Other Accounting standards adopted effective January 1, 2021 ASU No. 2019-12: Income Taxes (Topic 740) Reduces the complexity over accounting for income taxes by removing certain exceptions and amending guidance to improve consistent application of accounting over income taxes. This guidance did not have a material impact on our consolidated financial statements and related disclosures upon adoption, but may in the future. This guidance was effective January 1, 2021. A table providing a brief description of recent ASUs to the ASC issued by the FASB that are pending adoption and deemed to have a possible material impact on our consolidated financial statements based on current account balances and activity follows: Standard Description Effect on the Financial Statements or Other Accounting standards issued pending adoption ASU No. 2020-04: Reference Rate Reform (Topic 848), as amended through January 2021 Provides temporary optional guidance to ease the potential burden in applying GAAP to contract modifications and hedging relationships that reference London Inter-Bank Offered Rate ("LIBOR") or another reference rate expected to be discontinued, subject to meeting certain criteria. We currently have interest rate derivative agreements with hedging relationships that reference LIBOR which extend past the fiscal year ended December 31, 2021. We are currently assessing the provisions of this guidance as LIBOR is still in place and do not expect that its adoption will have a material impact on our consolidated financial statements and related disclosures. This guidance will be in effect from March 12, 2020 through December 31, 2022.

REVENUE RECOGNITION

REVENUE RECOGNITION	6 Months Ended
	Jun. 30, 2021
Revenue from Contract with Customer [Abstract]
REVENUE RECOGNITION	REVENUE RECOGNITION Revenues associated with our solid waste operations are derived mainly from solid waste collection and disposal, landfill, landfill gas-to-energy, processing, transfer and recycling services in the northeastern United States. Effective January 1, 2021, we reorganized the Resource Solutions operating segment, which includes our larger-scale recycling and commodity brokerage operations along with our organics services and large scale commercial and industrial services, from our historical lines-of-service of recycling, organics and customer solutions into two lines-of-service: processing and non-processing. Processing services consist of the receipt of recycled, sludge or other organic materials at one of our materials recovery, processing or disposal facilities, where it is then sorted, mixed and/or processed, and then disposed of or sold. Revenues from processing services are derived from municipalities and customers in the form of processing fees, tipping fees, commodity sales, and organic material sales. Revenues from non-processing services are derived from brokerage services; overall resource management services providing a wide range of environmental services and zero waste solutions to large and complex organizations; and traditional collection, disposal and recycling services provided to large account multi-site customers. In brokerage arrangements, we act as an agent that facilitates the sale of recyclable materials between an inbound customer and an outbound customer. Revenues from the brokerage of recycled materials are recognized on a net basis at the time of shipment. In general, these fees are variable in nature. Classification of revenues by service line reported in the three and six months ended June 30, 2020 has been reclassified to conform with the presentation for the three and six months ended June 30, 2021. A table of revenues disaggregated by service line and timing of revenue recognition by operating segment for each of the three and six months ended June 30, 2021 and 2020 follows: Three Months Ended June 30, 2021 Eastern Western Resource Solutions Total Revenues Collection $ 39,364 $ 67,963 $ — $ 107,327 Landfill 6,118 16,517 — 22,635 Transfer 13,475 9,976 — 23,451 Transportation 47 3,040 — 3,087 Landfill gas-to-energy 246 854 — 1,100 Processing 1,808 502 21,031 23,341 Non-processing — — 34,934 34,934 Total revenues $ 61,058 $ 98,852 $ 55,965 $ 215,875 Transferred at a point-in-time $ 38 $ 487 $ 14,944 $ 15,469 Transferred over time 61,020 98,365 41,021 200,406 Total revenues $ 61,058 $ 98,852 $ 55,965 $ 215,875 Three Months Ended June 30, 2020 Eastern Western Resource Solutions Total Revenues Collection $ 35,463 $ 58,545 $ — $ 94,008 Landfill 4,568 15,218 — 19,786 Transfer 11,451 9,003 — 20,454 Transportation 52 3,454 — 3,506 Landfill gas-to-energy 197 721 — 918 Processing 1,605 345 16,205 18,155 Non-processing — — 31,940 31,940 Total revenues $ 53,336 $ 87,286 $ 48,145 $ 188,767 Transferred at a point-in-time $ 69 $ 367 $ 8,231 $ 8,667 Transferred over time 53,267 86,919 39,914 180,100 Total revenues $ 53,336 $ 87,286 $ 48,145 $ 188,767 Six Months Ended June 30, 2021 Eastern Western Resource Solutions Total Revenues Collection $ 75,440 $ 129,356 $ — $ 204,796 Landfill 11,520 30,136 — 41,656 Transfer 22,899 17,123 — 40,022 Transportation 95 5,253 — 5,348 Landfill gas-to-energy 515 1,888 — 2,403 Processing 2,934 860 38,302 42,096 Non-processing — — 69,085 69,085 Total revenues $ 113,403 $ 184,616 $ 107,387 $ 405,406 Transferred at a point-in-time $ 82 $ 988 $ 25,036 $ 26,106 Transferred over time 113,321 183,628 82,351 379,300 Total revenues $ 113,403 $ 184,616 $ 107,387 $ 405,406 Six Months Ended June 30, 2020 Eastern Western Resource Solutions Total Revenues Collection $ 71,400 $ 117,168 $ — $ 188,568 Landfill 8,112 31,528 — 39,640 Transfer 20,834 15,673 — 36,507 Transportation 99 6,125 — 6,224 Landfill gas-to-energy 583 1,361 — 1,944 Processing 2,451 636 30,023 33,110 Non-processing — — 65,683 65,683 Total revenues $ 103,479 $ 172,491 $ 95,706 $ 371,676 Transferred at a point-in-time $ 125 $ 602 $ 12,692 $ 13,419 Transferred over time 103,354 171,889 83,014 358,257 Total revenues $ 103,479 $ 172,491 $ 95,706 $ 371,676 Payments to customers that are not in exchange for a distinct good or service are recorded as a reduction of revenues. Rebates to certain customers associated with payments for recycled or organic materials that are received and subsequently processed and sold to other third-parties amounted to $2,532 and $4,100 in the three and six months ended June 30, 2021, respectively, and $1,546 and $2,537 in the three and six months ended June 30, 2020, respectively. Rebates are generally recorded as a reduction of revenues upon the sale of such materials, or upon receipt of the recycled materials at our facilities. We did not record any revenues in the three and six months ended June 30, 2021 or June 30, 2020 from performance obligations satisfied in previous periods. Contract receivables, which are included in Accounts receivable, net are recorded when billed or when related revenue is earned, if earlier, and represent claims against third-parties that will be settled in cash. Accounts receivable, net includes gross receivables from contracts of $79,712 and $74,162 as of June 30, 2021 and December 31, 2020, respectively. Certain customers are billed in advance and, accordingly, recognition of the related revenues is deferred as a contract liability until the services are provided and control transferred to the customer. We recognized contract liabilities of $3,133 and $2,685 as of June 30, 2021 and December 31, 2020, respectively. Due to the short term nature of advanced billings, substantially all of the deferred revenue recognized as a contract liability as of December 31, 2020 and December 31, 2019 was recognized as revenue during the six months ended June 30, 2021 and June 30, 2020, respectively, when the services were performed.

BUSINESS COMBINATIONS

BUSINESS COMBINATIONS	6 Months Ended
	Jun. 30, 2021
Business Combination and Asset Acquisition [Abstract]
BUSINESS COMBINATIONS	BUSINESS COMBINATIONS On July 26, 2021, we acquired Willimantic Waste Paper Co., Inc. ("Willimantic"), a residential, commercial and roll-off collection business in eastern Connecticut. Willimantic also operates a rail-served construction and demolition processing and waste transfer facility, a waste transfer station, a single stream recycling facility, and several other recycling operations. In the six months ended June 30, 2021, we acquired two tuck-in solid waste collection businesses in our Western region, along with a septic and portable toilet business and a tuck-in solid waste collection business in our Eastern region. In the six months ended June 30, 2020, we acquired four businesses: three tuck-in solid waste collection businesses in our Western region and one recycling operation in our Resource Solutions operating segment. The operating results of the acquired businesses are included in the accompanying unaudited consolidated statements of operations from each date of acquisition, and the purchase price has been allocated to the net assets acquired based on fair values at each date of acquisition, with the residual amounts recorded as goodwill. Acquired intangible assets other than goodwill that are subject to amortization include client lists and non-compete covenants. Such assets are amortized over a five-year to ten-year period from the date of acquisition. All amounts recorded to goodwill, except goodwill related to certain acquisitions, are expected to be deductible for tax purposes. A summary of the purchase price paid and the purchase price allocation for these acquisitions follows: Six Months Ended 2021 2020 Purchase Price: Cash used in acquisitions, net of cash acquired $ 4,378 $ 19,212 Holdbacks 505 2,837 Total 4,883 22,049 Allocated as follows: Current assets 13 132 Land — 685 Buildings — 2,118 Equipment 1,549 8,277 Intangible assets 1,646 5,912 Other liabilities, net (82) (222) Fair value of assets acquired and liabilities assumed 3,126 16,902 Excess purchase price allocated to goodwill $ 1,757 $ 5,147 Certain purchase price allocations are preliminary and are based on information existing at the acquisition dates or upon closing the transaction. Accordingly, these purchase price allocations are subject to change. Unaudited pro forma combined information that shows our operational results as though each acquisition completed since the beginning of the prior fiscal year had occurred as of January 1, 2020 is as follows: Three Months Ended Six Months Ended 2021 2020 2021 2020 Revenues $ 216,082 $ 192,610 $ 406,242 $ 380,791 Operating income $ 21,955 $ 17,629 $ 34,019 $ 24,880 Net income $ 11,787 $ 12,181 $ 16,129 $ 13,220 Basic earnings per share attributable to common stockholders: Weighted average common shares outstanding 51,366 48,348 51,273 48,176 Basic earnings per common share $ 0.23 $ 0.25 $ 0.31 $ 0.27 Diluted earnings per share attributable to common stockholders: Weighted average common shares outstanding 51,546 48,563 51,466 48,411 Diluted earnings per common share $ 0.23 $ 0.25 $ 0.31 $ 0.27 The unaudited pro forma results set forth in the table above have been prepared for comparative purposes only and are not necessarily indicative of the actual results of operations had the acquisitions occurred as of January 1, 2020 or of the results of our future operations. Furthermore, the unaudited pro forma results do not give effect to all cost savings or incremental costs that may occur as a result of the integration and consolidation of the completed acquisitions.

GOODWILL AND INTANGIBLE ASSETS

GOODWILL AND INTANGIBLE ASSETS	6 Months Ended
	Jun. 30, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
GOODWILL AND INTANGIBLE ASSETS	GOODWILL AND INTANGIBLE ASSETS A summary of the activity and balances related to goodwill by reporting segment is as follows: December 31, Acquisitions June 30, Eastern region $ 30,873 $ 46 $ 30,919 Western region 149,984 1,739 151,723 Resource solutions 14,044 — 14,044 Total $ 194,901 $ 1,785 $ 196,686 Summaries of intangible assets by type follows: Covenants Client Lists Total Balance, June 30, 2021 Intangible assets $ 27,390 $ 80,036 $ 107,426 Less accumulated amortization (21,323) (30,176) (51,499) $ 6,067 $ 49,860 $ 55,927 Covenants Client Lists Total Balance, December 31, 2020 Intangible assets $ 26,971 $ 78,809 $ 105,780 Less accumulated amortization (20,547) (26,909) (47,456) $ 6,424 $ 51,900 $ 58,324 Intangible amortization expense was $2,015 and $4,043 during the three and six months ended June 30, 2021, respectively, and $2,222 and $4,316 during the three and six months ended June 30, 2020, respectively. A summary of intangible amortization expense estimated for the five fiscal years following fiscal year 2020 and thereafter follows: Estimated Future Amortization Expense as of June 30, 2021 Fiscal year ending December 31, 2021 $ 4,038 Fiscal year ending December 31, 2022 $ 7,440 Fiscal year ending December 31, 2023 $ 7,183 Fiscal year ending December 31, 2024 $ 8,098 Fiscal year ending December 31, 2025 $ 8,301 Thereafter $ 20,867

ACCRUED FINAL CAPPING, CLOSURE

ACCRUED FINAL CAPPING, CLOSURE AND POST CLOSURE	6 Months Ended
	Jun. 30, 2021
Asset Retirement Obligation Disclosure [Abstract]
ACCRUED FINAL CAPPING, CLOSURE AND POST CLOSURE	ACCRUED FINAL CAPPING, CLOSURE AND POST CLOSUREAccrued final capping, closure and post-closure costs include the current and non-current portion of costs associated with obligations for final capping, closure and post-closure of our landfills. We estimate our future final capping, closure and post-closure costs in order to determine the final capping, closure and post-closure expense per ton of waste placed into each landfill. The anticipated time frame for paying these costs varies based on the remaining useful life of each landfill as well as the duration of the post-closure monitoring period. A summary of the changes to accrued final capping, closure and post-closure liabilities follows: Six Months Ended 2021 2020 Beginning balance $ 82,533 $ 71,927 Obligations incurred 2,319 1,764 Revision in estimates (1) — 152 Accretion expense 3,676 3,204 Obligations settled (2) (2,969) (1,650) Ending balance $ 85,559 $ 75,397 (1) Relates to changes in estimated costs and timing of final capping, closure and post-closure activities at the Town of Southbridge, Massachusetts landfill. See Note 8, Commitments and Contingencies and Note 11, Other Items and Charges for further discussion. (2) May include amounts that are being processed through accounts payable as a part of our disbursements cycle.

DEBT

DEBT	6 Months Ended
	Jun. 30, 2021
Debt And Derivatives Disclosure [Abstract]
DEBT	DEBT A summary of debt is as follows: June 30, December 31, Senior Secured Credit Facility: Revolving line of credit facility ("Revolving Credit Facility") due May 2023; bearing interest at LIBOR plus 1.50% $ — $ — Term loan A facility ("Term Loan Facility") due May 2023; bearing interest at LIBOR plus 1.50% 348,250 350,000 Tax-Exempt Bonds: New York State Environmental Facilities Corporation Solid Waste Disposal Revenue Bonds Series 2014 ("New York Bonds 2014R-1") due December 2044 - fixed rate interest period through 2029; bearing interest at 2.875% 25,000 25,000 New York State Environmental Facilities Corporation Solid Waste Disposal Revenue Bonds Series 2014R-2 ("New York Bonds 2014R-2") due December 2044 - fixed rate interest period through 2026; bearing interest at 3.125% 15,000 15,000 New York State Environmental Facilities Corporation Solid Waste Disposal Revenue Bonds Series 2020 ("New York Bonds 2020") due September 2050 - fixed rate interest period through 2025; bearing interest at 2.750% 40,000 40,000 Finance Authority of Maine Solid Waste Disposal Revenue Bonds Series 2005R-3 ("FAME Bonds 2005R-3") due January 2025 - fixed rate interest period through 2025; bearing interest at 5.25% 25,000 25,000 Finance Authority of Maine Solid Waste Disposal Revenue Bonds Series 2015R-1 ("FAME Bonds 2015R-1") due August 2035 - fixed rate interest period through 2025; bearing interest at 5.125% 15,000 15,000 Finance Authority of Maine Solid Waste Disposal Revenue Bonds Series 2015R-2 ("FAME Bonds 2015R-2") due August 2035 - fixed rate interest period through 2025; bearing interest at 4.375% 15,000 15,000 Vermont Economic Development Authority Solid Waste Disposal Long-Term Revenue Bonds Series 2013 ("Vermont Bonds") due April 2036 - fixed rate interest period through 2028; bearing interest at 4.625% 16,000 16,000 Business Finance Authority of the State of New Hampshire Solid Waste Disposal Revenue Bonds Series 2013 ("New Hampshire Bonds") due April 2029 - fixed rate interest period through 2029; bearing interest at 2.95% 11,000 11,000 Other: Finance leases maturing through December 2107; bearing interest at a weighted average of 4.0% 34,467 31,486 Notes payable maturing through June 2027; bearing interest at a weighted average of 3.4% 4,454 4,933 Principal amount of debt 549,171 548,419 Less—unamortized debt issuance costs (1) 7,625 8,768 Debt less unamortized debt issuance costs 541,546 539,651 Less—current maturities of debt 14,716 9,240 $ 526,830 $ 530,411 (1) A summary of unamortized debt issuance costs by debt instrument follows: June 30, December 31, Revolving Credit Facility and Term Loan Facility (collectively, the "Credit Facility") $ 3,019 $ 3,839 New York Bonds 2014R-1 967 1,000 New York Bonds 2014R-2 298 329 New York Bonds 2020 1,372 1,461 FAME Bonds 2005R-3 305 347 FAME Bonds 2015R-1 452 482 FAME Bonds 2015R-2 304 343 Vermont Bonds 460 487 New Hampshire Bonds 448 480 $ 7,625 $ 8,768 Credit Facility As of June 30, 2021, we are party to a credit agreement ("Credit Agreement"), which provides for a $350,000 aggregate principal amount Term Loan Facility and a $200,000 Revolving Credit Facility. We have the right to request, at our discretion, an increase in the amount of loans under the Credit Facility by an aggregate amount of $125,000, subject to the terms and conditions set forth in the Credit Agreement. The Credit Facility has a 5-year term that matures in May 2023 and bears interest at a rate of LIBOR plus 1.50% per annum, which will be reduced to a rate of LIBOR plus as low as 1.25% upon us reaching a consolidated net leverage ratio of less than 2.25x. The Credit Facility is guaranteed jointly and severally, fully and unconditionally by all of our significant wholly-owned subsidiaries and secured by substantially all of our assets. As of June 30, 2021, further advances were available under the Credit Facility in the amount of $173,575. The available amount is net of outstanding irrevocable letters of credit totaling $26,425, at which date no amount had been drawn. The Credit Agreement requires us to maintain a minimum interest coverage ratio and a maximum consolidated net leverage ratio, to be measured at the end of each fiscal quarter. As of June 30, 2021, we were in compliance with the covenants contained in the Credit Agreement. In addition to these financial covenants, the Credit Agreement also contains a number of important customary affirmative and negative covenants which restrict, among other things, our ability to sell assets, incur additional debt, create liens, make investments, and pay dividends. We do not believe that these restrictions impact our ability to meet future liquidity needs. Cash Flow Hedges Our strategy to reduce exposure to interest rate risk involves entering into interest rate derivative agreements to hedge against adverse movements in interest rates related to the variable rate portion of our long-term debt. We have designated these derivative instruments as highly effective cash flow hedges, and therefore the change in fair value is recorded in our stockholders’ equity as a component of accumulated other comprehensive loss and included in interest expense at the same time as interest expense is affected by the hedged transactions. Differences paid or received over the life of the agreements are recorded as additions to or reductions of interest expense on the underlying debt and included in cash flows from operating activities. As of June 30, 2021 and December 31, 2020, our active interest rate derivative agreements had total notional amounts of $195,000 and $190,000, respectively. According to the terms of the agreements, we receive interest based on the 1-month LIBOR index and pay interest at a weighted average rate of approximately 2.51% as of June 30, 2021. The agreements mature between February 2022 and December 2026. As of June 30, 2021 and December 31, 2020, we had forward starting interest rate derivative agreements with total notional amounts of $85,000 and $125,000, respectively. According to the terms of the agreements, we receive interest based on the 1-month LIBOR index, restricted by a 0.0% floor, and will pay interest at a weighted average rate of approximately 1.55%. The agreements mature between February 2027 and May 2028. A summary of the effect of cash flow hedges related to derivative instruments on the consolidated balance sheet follows: Fair Value Balance Sheet Location June 30, December 31, Interest rate swaps Other non-current assets $ 153 $ — Interest rate swaps Other accrued liabilities $ 4,776 $ 4,774 Interest rate swaps Other long-term liabilities 3,959 8,463 $ 8,735 $ 13,237 Interest rate swaps Accumulated other comprehensive loss, net of tax $ (8,782) $ (13,434) Interest rate swaps - tax effect Accumulated other comprehensive loss, net of tax 860 1,917 $ (7,922) $ (11,517) A summary of the amount of expense on cash flow hedging relationships related to interest rate swaps reclassified from accumulated other comprehensive loss into earnings follows: Three Months Ended Six Months Ended Statement of Operations Location 2021 2020 2021 2020 Interest expense $ 1,202 $ 990 $ 2,347 $ 1,357

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	6 Months Ended
	Jun. 30, 2021
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES In the ordinary course of our business and as a result of the extensive governmental regulation of the solid waste industry, we are subject to various judicial and administrative proceedings involving state and local agencies. In these proceedings, an agency may seek to impose fines or to revoke or deny renewal of an operating permit held by us. From time to time, we may also be subject to actions brought by special interest or other groups, adjacent landowners or residents in connection with the permitting and licensing of landfills and transfer stations, or allegations of environmental damage or violations of the permits and licenses pursuant to which we operate. In addition, we may be named defendants in various claims and suits pending for alleged damages to persons and property, alleged violations of certain laws and alleged liabilities arising out of matters occurring during the ordinary operation of a waste management business. In accordance with FASB ASC 450 - Contingencies, we accrue for legal proceedings, inclusive of legal costs, when losses become probable and reasonably estimable. As of the end of each applicable reporting period, we review each of our legal proceedings to determine whether it is probable, reasonably possible or remote that a liability has been incurred and, if it is at least reasonably possible, whether a range of loss can be reasonably estimated under the provisions of FASB ASC 450-20. In instances where we determine that a loss is probable and we can reasonably estimate a range of loss we may incur with respect to such a matter, we record an accrual for the amount within the range that constitutes our best estimate of the possible loss. If we are able to reasonably estimate a range, but no amount within the range appears to be a better estimate than any other, we record an accrual in the amount that is the low end of such range. When a loss is reasonably possible, but not probable, we will not record an accrual, but we will disclose our estimate of the possible range of loss where such estimate can be made in accordance with FASB ASC 450-20. Environmental Remediation Liability We are subject to liability for environmental damage, including personal injury and property damage, that our solid waste, recycling and power generation facilities may cause to neighboring property owners, particularly as a result of the contamination of drinking water sources or soil, possibly including damage resulting from conditions that existed before we acquired the facilities. We may also be subject to liability for similar claims arising from off-site environmental contamination caused by pollutants or hazardous substances if we or our predecessors arrange or arranged to transport, treat or dispose of those materials. The following matters represent our material outstanding claims. Southbridge Recycling & Disposal Park, Inc. In October 2015, our Southbridge Recycling and Disposal Park, Inc. (“SRD”) subsidiary reported to the Massachusetts Department of Environmental Protection (“MADEP”) results of analysis of samples collected pursuant to our existing permit from private drinking water wells located near the Town of Southbridge, Massachusetts (“Town”) Landfill (“Southbridge Landfill”), which was operated by SRD and later closed in November 2018 when Southbridge Landfill reached its final capacity. Those results indicated the presence of contaminants above the levels triggering notice and response obligations under MADEP regulations. In response to those results, we carried out an Immediate Response Action pursuant to Massachusetts General Law Chapter 21E (the "Charlton 21E Obligations"). Further, we implemented a plan to analyze and better understand the groundwater near the Southbridge Landfill and we investigated with the objective of identifying the source or sources of the elevated levels of contamination measured in the well samples. We entered into an Administrative Consent Order on April 26, 2017 (the “ACO”), with MADEP, the Town, and the Town of Charlton, committing us to equally share the costs with MADEP, of up to $10,000 ($5,000 each) for the Town to install a municipal waterline in the Town of Charlton ("Waterline"). Upon satisfactory completion of that Waterline, and other matters covered by the ACO, we and the Town will be released by MADEP from any future responsibilities for the Charlton 21E Obligations. We also entered into an agreement with the Town on April 28, 2017 entitled the “21E Settlement and Water System Construction Funding Agreement” (the “Waterline Agreement”), wherein we and the Town released each other from claims arising from the Charlton 21E Obligations. Pursuant to the Waterline Agreement, the Town issued a twenty (20) year bond for our portion of the Waterline costs in the amount of $4,089. We have agreed to reimburse the Town for periodic payments under such bond. Construction of the Waterline is complete and homeowners are relying on municipal water supply. Bond reimbursement to the Town commenced in the quarter ended June 30, 2020. We have recorded an environmental remediation liability related to our obligation associated with installation of the Waterline in other accrued liabilities and other long-term liabilities. We inflate the estimated costs in current dollars to the expected time of payment and discount the total cost to present value using a risk-free interest rate of 2.6%. Our expenditures could be significantly higher if costs exceed estimates. A summary of the changes to the environmental remediation liability associated with the Southbridge Landfill follows: Six Months Ended 2021 2020 Beginning balance $ 4,261 $ 4,596 Accretion expense 56 62 Obligations incurred — 28 Revision in estimates (1) — (188) Obligations settled (2) (281) (293) Ending balance $ 4,036 $ 4,205 (1) The revision in estimates is associated with the completion of the environmental remediation at the site. See Note 11, Other Items and Charges to our consolidated financial statements for further discussion. (2) May include amounts that are being processed through accounts payable as a part of our disbursements cycle. The costs and liabilities we may be required to incur in connection with the foregoing Southbridge Landfill matters could be material to our results of operations, our cash flows and our financial condition. Potsdam Environmental Remediation Liability On December 20, 2000, the State of New York Department of Environmental Conservation (“DEC”) issued an Order on Consent (“Order”) which named Waste-Stream, Inc. (“WSI”), our subsidiary, General Motors Corporation and Niagara Mohawk Power Corporation (“NiMo”) as Respondents. The Order required that the Respondents undertake certain work on a 25-acre scrap yard and solid waste transfer station owned by WSI in Potsdam, New York, including the preparation of a Remedial Investigation and Feasibility Study (“Study”). A draft of the Study was submitted to the DEC in January 2009 (followed by a final report in May 2009). The Study estimated that the undiscounted costs associated with implementing the preferred remedies would be approximately $10,219. On February 28, 2011, the DEC issued a Proposed Remedial Action Plan for the site and accepted public comments on the proposed remedy through March 29, 2011. We submitted comments to the DEC on this matter. In April 2011, the DEC issued the final Record of Decision (“ROD”) for the site. The ROD was subsequently rescinded by the DEC for failure to respond to all submitted comments. The preliminary ROD, however, estimated that the present cost associated with implementing the preferred remedies would be approximately $12,130. The DEC issued the final ROD in June 2011 with proposed remedies consistent with its earlier ROD. An Order on Consent and Administrative Settlement naming WSI and NiMo as Respondents was executed by the Respondents and DEC with an effective date of October 25, 2013. On January 29, 2016, a Cost-Sharing Agreement was executed between WSI, NiMo, Alcoa Inc. (“Alcoa”) and Reynolds Metal Company (“Reynolds”) whereby Alcoa and Reynolds elected to voluntarily participate in the onsite remediation activities at a combined 15% participant share. The majority of the remediation work has been completed as of June 30, 2021. WSI is jointly and severally liable with NiMo, Alcoa and Reynolds for the total cost to remediate. We have recorded an environmental remediation liability associated with the Potsdam site based on incurred costs to date and estimated costs to complete the remediation in other accrued liabilities and other long-term liabilities. We inflate the estimated costs in current dollars to the expected time of payment and discount the total cost to present value using a risk-free interest rate of 1.9%. The environmental remediation liability associated with the Potsdam site was $939 as of both June 30, 2021 and December 31, 2020. Legal Proceedings North Country Environmental Services On or about March 8, 2018, NELC and the Conservation Law Foundation ("CLF") (the "NH Citizen Groups") delivered correspondence to our subsidiary, North Country Environmental Services, Inc. ("NCES"), and us, providing notice of the NH Citizen Groups' intent to sue NCES and us for violations of the CWA in conjunction with NCES's operation of its landfill in Bethlehem, New Hampshire ("NCES Landfill"). On May 14, 2018, the NH Citizen Groups filed a lawsuit against NCES and us in the United States District Court for the District of New Hampshire (the “New Hampshire Court”) alleging violations of the CWA, arguing that ground water discharging into the Ammonoosuc River is a "point source" under the CWA (the "New Hampshire Litigation"). The New Hampshire Litigation seeks remediation and fines under the CWA and an order requiring NCES to seek a Federal National Pollutant Discharge Elimination System permit for the operation of the NCES Landfill. On June 15, 2018, we and NCES filed a Motion to Dismiss the New Hampshire Litigation. On July 13, 2018, the NH Citizen Groups filed objections to our Motion to Dismiss. On July 27, 2018, we filed a reply in support of our Motion to Dismiss. On September 25, 2018, the New Hampshire Court denied our Motion to Dismiss. In March of 2019, we filed a motion in the New Hampshire Litigation asking for a stay of this litigation until certain appeals from discordant federal circuit courts were heard by the Supreme Court of the United States (“SCOTUS”), in the case identified as “County of Maui v. Hawaii Wildlife Fund (“MAUI”)". Our motion for a stay was granted in the New Hampshire Litigation, and SCOTUS heard the case in 2019 and issued a ruling on April 23, 2020. SCOTUS remanded the case to the U.S. Court of Appeals for the Ninth Circuit in San Francisco (the “Circuit Court”) ruling that the Circuit Court’s standard as to whether ground water impacts to navigable waters is too broad. We do not believe that the MAUI decision resolves the issues presented in the New Hampshire Litigation, and until the Circuit Court rules in the remanded MAUI case, we intend to continue to vigorously defend against the New Hampshire Litigation, which we believe is without merit. The NH Citizens Groups filed a motion with the New Hampshire Court on July 15, 2020 to amend their complaint based on MAUI. The New Hampshire Court granted the NH Citizen Groups' motion on September 2, 2020 and encouraged the parties to file motions for summary judgment. We filed our Motion for Summary Judgment on November 20, 2020 and the NH Citizens Groups filed a Motion for Summary Judgment on February 19, 2021. A hearing on motions for summary judgment was held on May 14, 2021. On May 24, 2021 the NH Citizens Group submitted a post-hearing filing requesting that the Court consider purported supplemental material facts discovered after the hearing, and to provide a response to questions posed by the Court at the hearing, in response to which we filed a Motion to Strike on June 2, 2021. The NH Citizens Group filed an Objection to the Motion to Strike on June 8, 2021. We filed a response on June 25, 2021. On October 9, 2020, NCES received a Type I-A Permit Modification for Expansion in the Stage VI area of the NCES Landfill (the “Permit”). On November 9, 2020, CLF filed an appeal of the Permit to the New Hampshire Waste Management Council (the “Council”)on the grounds it failed to meet the public benefit criteria. On January 19, 2021, CLF filed a Complaint for Injunctive Relief with the Grafton Superior Court to enjoin NCES from accepting waste pursuant to the new Permit until such a time as CLF has exhausted its appeal rights. A hearing on the Complaint for Injunctive Relief was held on March 10, 2021; the Grafton Superior Court denied the motion on May 14, 2021. CLF did not appeal this decision. The Council denied NCES’s Motion to Dismiss CLF’s appeal for lack of standing by Order dated March 17, 2021. NCES filed a Motion to Reconsider on March 26, 2021, which was denied by the Council on May 11, 2021. A prehearing conference was held and a schedule for the case was established on June 8, 2021. NCES filed a Motion to Dismiss on the merits of the appeal on June 30, 2021, and will continue to vigorously defend against this litigation pending the Council’s ruling. Hakes Landfill Litigation On or about December 19, 2019, the New York State Department of Environmental Conservation (“Department”) issued certain permits to us to expand the landfill owned and operated by Hakes C&D Disposal Inc. in the Town of Campbell, Steuben County, New York (“Hakes Landfill”). The permits authorize approximately five years of expansion capacity at the Hakes Landfill. The authorizations issued by the Department followed approvals issued by the Town of Campbell Planning Board (“Planning Board”) in January 2019, and the Town Board of the Town of Campbell (“Town Board”) in March 2019, granting site plan review and a zoning change for the project. Litigation was commenced by the Sierra Club, several other non-governmental organizations, and several individuals (“the Petitioners”), challenging the approvals issued by the Department, the Planning Board and the Town Board in New York State Supreme Court, Steuben County (the “Hakes Litigation”). The challenge was based upon allegations that the agencies issuing these approvals did not follow the requirements of Article 8 of the Environmental Conservation Law of the State of New York, the State Environmental Quality Review Act (“SEQRA”), by failing to address certain radioactivity issues alleged by Petitioners to be associated with certain drilling wastes authorized for disposal at the Hakes Landfill. The Department opposed the Hakes Litigation on procedural grounds. We and the Town of Campbell opposed the Hakes Litigation on the merits, and on July 31, 2020, the Court dismissed the Hakes Litigation on the merits. The Petitioners filed a notice of appeal. The time to appeal expired on February 10, 2021, and the attorney for the Petitioners confirmed that they are not pursuing the appeal. Accordingly, all approvals issued for the expansion project are now final and binding. Ontario County, New York Class Action Litigation On or about September 17, 2019, Richard Vandemortel and Deb Vandemortel ("Named Plaintiffs") filed a class action complaint against us in Ontario County Supreme Court (the "New York Court") on behalf of similarly situated citizens ("Class Members") in Ontario County, New York (the "New York Litigation"). The New York Litigation alleges that over one thousand (1,000) citizens constitute the putative class in the New York Litigation, and it seeks damages for diminution of property values and infringement of the putative class’ rights to live without interference to their daily lives due to odors emanating from the Subtitle D landfill located in Seneca, New York , which is operated by us pursuant to a long-term Operation, Maintenance and Lease Agreement with Ontario County. The New York Litigation was served on us on October 14, 2019, and the parties commenced settlement negotiations in early 2020. On December 1, 2020, the parties entered into a settlement agreement (the "Settlement Agreement") and thereafter the Named Plaintiffs and Class Members' counsel ("Counsel") moved the New York Court for entry of the Order on Notice/Preliminary Approvals. A settlement fairness hearing was held on July 7, 2021, and the judge issued an Order and Final Judgment that was filed on July 8, 2021. The settlement includes a $750 payment to a Qualified Settlement Fund for the benefit of Counsel and one-time lump sum payments to the Named Plaintiffs and Class Members who opt into the Settlement Agreement. We also committed $900 in expenses and capital improvements for remediation measures to be completed by December 31, 2022. Conservation Law Foundation, Inc. v Robert R. Scott, Commissioner, New Hampshire Department of Environmental Services

STOCKHOLDERS' EQUITY

STOCKHOLDERS' EQUITY	6 Months Ended
	Jun. 30, 2021
Equity [Abstract]
STOCKHOLDERS' EQUITY	STOCKHOLDERS' EQUITY Stock Based Compensation Shares Available For Issuance In the fiscal year ended December 31, 2016, we adopted the 2016 Incentive Plan (“2016 Plan”). Under the 2016 Plan, we may grant awards up to an aggregate amount of shares equal to the sum of: (i) 2,250 shares of Class A common stock (subject to adjustment in the event of stock splits and other similar events), plus (ii) such additional number of shares of Class A common stock (up to 2,723 shares) as is equal to the sum of the number of shares of Class A common stock that remained available for grant under the 2006 Stock Incentive Plan (“2006 Plan”) immediately prior to the expiration of the 2006 Plan and the number of shares of Class A common stock subject to awards granted under the 2006 Plan that expire, terminate or are otherwise surrendered, canceled, forfeited or repurchased by us. As of June 30, 2021, there were 947 Class A common stock equivalents available for future grant under the 2016 Plan. Stock Options Stock options are granted at a price equal to the prevailing fair value of our Class A common stock at the date of grant. Generally, stock options granted have a term not to exceed ten years and vest over a one-year to four-year period from the date of grant. The fair value of each stock option granted is estimated using a Black-Scholes option-pricing model, which requires extensive use of accounting judgment and financial estimation, including estimates of the expected term stock option holders will retain their vested stock options before exercising them and the estimated volatility of our Class A common stock price over the expected term. A summary of stock option activity follows: Stock Options Weighted Average Exercise Price Weighted Average Remaining Contractual Term (years) Aggregate Intrinsic Value Outstanding, December 31, 2020 90 $ 8.91 Granted — $ — Exercised (9) $ 12.48 Forfeited — $ — Outstanding, June 30, 2021 81 $ 8.51 4.1 $ 4,455 Exercisable, June 30, 2021 81 $ 8.51 4.1 $ 4,455 We did not record any stock-based compensation expense for stock options during each of the three and six months ended June 30, 2021 and June 30, 2020. As of June 30, 2021, we had no unrecognized stock-based compensation expense related to outstanding stock options. During both the three and six months ended June 30, 2021, the aggregate intrinsic value of stock options exercised was $448. Other Stock Awards Restricted stock awards, restricted stock units and performance stock units, with the exception of market-based performance stock units, are granted at a price equal to the fair value of our Class A common stock at the date of grant. The fair value of each market-based performance stock unit is estimated using a Monte Carlo pricing model, which requires extensive use of accounting judgment and financial estimation, including the estimated share price appreciation plus the value of dividends of our Class A common stock as compared to the Russell 2000 Index over the requisite service period. Generally, restricted stock awards granted to non-employee directors vest incrementally over a three year period beginning on the first anniversary of the date of grant. Restricted stock units granted to non-employee directors vest in full on the first anniversary of the grant date. Restricted stock units granted to employees vest incrementally over an identified service period beginning on the grant date based on continued employment. Performance stock units granted to employees, including market-based performance stock units, vest at a future date following the grant date and are based on the attainment of performance targets and market achievements, as applicable. A summary of restricted stock, restricted stock unit and performance stock unit activity follows: Restricted Stock, Restricted Stock Units, and Performance Stock Units (1) Weighted Weighted Average Remaining Contractual Term (years) Aggregate Intrinsic Value Outstanding, December 31, 2020 307 $ 41.55 Granted 101 $ 67.36 Class A Common Stock Vested (81) $ 35.28 Forfeited (8) $ 51.31 Outstanding, June 30, 2021 319 $ 51.10 1.9 $ 20,233 Unvested, June 30, 2021 584 $ 51.01 1.7 $ 37,062 (1) Market-based performance stock unit grants are included at the 100% attainment level. Attainment of the maximum performance targets and market achievements would result in the issuance of an additional 265 shares of Class A common stock currently included in unvested. Stock-based compensation expense related to restricted stock, restricted stock units and performance stock units was $3,044 and $5,928 during the three and six months ended June 30, 2021, respectively, as compared to $1,763 and $3,277 during the three and six months ended June 30, 2020, respectively. During the three and six months ended June 30, 2021, the total fair value of other stock awards vested was $887 and $5,292, respectively. As of June 30, 2021, total unrecognized stock-based compensation expense related to outstanding restricted stock was $108, which will be recognized over a weighted average period of 2.3 years. As of June 30, 2021, total unrecognized stock-based compensation expense related to outstanding restricted stock units was $5,315, which will be recognized over a weighted average period of 1.9 years. As of June 30, 2021, total expected unrecognized stock-based compensation expense related to outstanding performance stock units was $9,006 to be recognized over a weighted average period of 1.9 years. We also recorded $72 and $128 of stock-based compensation expense related to our Amended and Restated 1997 Employee Stock Purchase Plan during the three and six months ended June 30, 2021, respectively, as compared to $56 and $103 during the three and six months ended June 30, 2020, respectively. Accumulated Other Comprehensive Loss, Net of Tax A summary of the changes in the balances of each component of accumulated other comprehensive loss, net of tax follows: Interest Rate Swaps Balance, December 31, 2020 $ (11,517) Other comprehensive income before reclassifications 2,305 Amounts reclassified from accumulated other comprehensive loss 2,347 Income tax provision related to items of other comprehensive income (1,057) Net current-period other comprehensive income 3,595 Balance, June 30, 2021 $ (7,922) A summary of reclassifications out of accumulated other comprehensive loss, net of tax follows: Three Months Ended Six Months Ended 2021 2020 2021 2020 Details About Accumulated Other Comprehensive Loss Components Amounts Reclassified Out of Accumulated Other Comprehensive Loss Affected Line Item in the Consolidated Interest rate swaps $ 1,202 $ 990 $ 2,347 $ 1,357 Interest expense (1,202) (990) (2,347) (1,357) Income before income taxes (142) — (269) 112 Provision for income taxes $ (1,060) $ (990) $ (2,078) $ (1,469) Net income

EARNINGS PER SHARE

EARNINGS PER SHARE	6 Months Ended
	Jun. 30, 2021
Earnings Per Share [Abstract]
EARNINGS PER SHARE	EARNINGS PER SHAREBasic earnings per share is computed by dividing net income by the weighted average number of common shares outstanding during the period. Diluted earnings per share is calculated based on the combined weighted average number of common shares and potentially dilutive shares, which include the assumed exercise of employee stock options, unvested restricted stock awards, unvested restricted stock units and unvested performance stock units, including market-based performance units based on the expected achievement of performance targets. In computing diluted earnings per share, we utilize the treasury stock method. A summary of the numerator and denominators used in the computation of earnings per share follows: Three Months Ended Six Months Ended 2021 2020 2021 2020 Numerator: Net income $ 11,783 $ 12,113 $ 16,094 $ 13,072 Denominators: Number of shares outstanding, end of period: Class A common stock 50,398 47,382 50,398 47,382 Class B common stock 988 988 988 988 Unvested restricted stock (2) (1) (2) (1) Effect of weighted average shares outstanding (18) (21) (111) (193) Basic weighted average common shares outstanding 51,366 48,348 51,273 48,176 Impact of potentially dilutive securities: Dilutive effect of stock options and other stock awards 180 215 193 235 Diluted weighted average common shares outstanding 51,546 48,563 51,466 48,411 Anti-dilutive potentially issuable shares — 12 48 12

OTHER ITEMS AND CHARGES

OTHER ITEMS AND CHARGES	6 Months Ended
	Jun. 30, 2021
Unusual or Infrequent Items, or Both [Abstract]
OTHER ITEMS AND CHARGES	OTHER ITEMS AND CHARGES Expense from Acquisition Activities In the three and six months ended June 30, 2021, we recorded charges of $1,632 and $2,046, respectively, and in the three and six months ended June 30, 2020 we recorded charges of $352 and $1,360, respectively, comprised primarily of legal, consulting and other similar costs associated with the acquisition and integration of acquired businesses or select development projects. Southbridge Landfill Closure Charge In 2017, we initiated the plan to cease operations of the Southbridge Landfill and later closed it in November 2018 when Southbridge Landfill reached its final capacity .

FAIR VALUE OF FINANCIAL INSTRUM

FAIR VALUE OF FINANCIAL INSTRUMENTS	6 Months Ended
	Jun. 30, 2021
Fair Value Disclosures [Abstract]
FAIR VALUE OF FINANCIAL INSTRUMENTS	FAIR VALUE OF FINANCIAL INSTRUMENTS We use a three-tier fair value hierarchy to classify and disclose all assets and liabilities measured at fair value on a recurring basis, as well as assets and liabilities measured at fair value on a non-recurring basis, in periods subsequent to their initial measurement. These tiers include: Level 1, defined as quoted market prices in active markets for identical assets or liabilities; Level 2, defined as inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities; and Level 3, defined as unobservable inputs that are not corroborated by market data. We use valuation techniques that maximize the use of market prices and observable inputs and minimize the use of unobservable inputs. In measuring the fair value of our financial assets and liabilities, we rely on market data or assumptions that we believe market participants would use in pricing an asset or a liability. Assets and Liabilities Accounted for at Fair Value Our financial instruments include cash and cash equivalents, accounts receivable, restricted investment securities held in trust on deposit with various banks as collateral for our obligations relative to our landfill final capping, closure and post-closure costs, interest rate swaps, trade payables and long-term debt. The carrying values of cash and cash equivalents, accounts receivable and trade payables approximate their respective fair values due to their short-term nature. The fair value of restricted investment securities held in trust, which are valued using quoted market prices, are included as restricted assets in the Level 1 tier below. The fair value of the interest rate swaps included in the Level 2 tier below is calculated using discounted cash flow valuation methodologies based upon the one-month LIBOR yield curves that are observable at commonly quoted intervals for the full term of the swaps. Recurring Fair Value Measurements Summaries of our financial assets and liabilities that are measured at fair value on a recurring basis follow: Fair Value Measurement at June 30, 2021 Using: Quoted Prices in Significant Other Significant Assets: Restricted investment securities - landfill closure $ 1,953 $ — $ — Interest rate swaps — 153 — $ 1,953 $ 153 $ — Liabilities: Interest rate swaps $ — $ 8,735 $ — Fair Value Measurement at December 31, 2020 Using: Quoted Prices in Significant Other Significant Assets: Restricted investment securities - landfill closure $ 1,848 $ — $ — Liabilities: Interest rate swaps $ — $ 13,237 $ — Fair Value of Debt As of June 30, 2021, the fair value of our fixed rate debt, including our FAME Bonds 2005R-3, FAME Bonds 2015R-1, FAME Bonds 2015R-2, Vermont Bonds, New York Bonds 2014R-1, New York Bonds 2014R-2, New York Bonds 2020 and New Hampshire Bonds was approximately $179,187 and the carrying value was $162,000. The fair value of the FAME Bonds 2005R-3, the FAME Bonds 2015R-1, the FAME Bonds 2015R-2, the Vermont Bonds, the New York Bonds 2014R-1, the New York Bonds 2014R-2, New York Bonds 2020 and the New Hampshire Bonds is considered to be Level 2 within the fair value hierarchy as the fair value is determined using market approach pricing provided by a third-party that utilizes pricing models and pricing systems, mathematical tools and judgment to determine the evaluated price for the security based on the market information of each of the bonds or securities with similar characteristics. As of June 30, 2021, the carrying value of our Term Loan Facility was $348,250 and the carrying value of our Revolving Credit Facility was $0. Their fair values are based on current borrowing rates for similar types of borrowing arrangements, or Level 2 inputs, and approximate their carrying values.

SEGMENT REPORTING

SEGMENT REPORTING	6 Months Ended
	Jun. 30, 2021
Segment Reporting [Abstract]
SEGMENT REPORTING	SEGMENT REPORTING We report selected information about our reportable operating segments in a manner consistent with that used for internal management reporting. We classify our solid waste operations on a geographic basis through regional operating segments, our Western and Eastern regions. Revenues associated with our solid waste operations are derived mainly from solid waste collection and disposal, landfill, landfill gas-to-energy, processing, transfer and recycling services in the northeastern United States. Effective January 1, 2021, we reorganized the Resource Solutions operating segment, which includes our larger-scale recycling and commodity brokerage operations along with our organics services and large scale commercial and industrial services, from our historical lines-of-service of recycling, organics and customer solutions into two lines-of-service: processing and non-processing. Revenues from processing services are derived from municipalities and customers in the form of processing fees, tipping fees, commodity sales, and organic material sales. Revenues from non-processing services are derived from brokerage services; overall resource management services providing a wide range of environmental services and zero waste solutions to large and complex organizations; and traditional collection, disposal and recycling services provided to large account multi-site customers. Revenues classification by service line reported in the three and six months ended June 30, 2020 has been reclassified to conform with the presentation for the three and six months ended June 30, 2021. Legal, tax, information technology, human resources, certain finance and accounting and other administrative functions are included in our Corporate Entities segment. Three Months Ended June 30, 2021 Segment Outside Inter-company Depreciation and Operating Total Eastern $ 61,058 $ 16,128 $ 7,313 $ 3,781 $ 226,157 Western 98,852 33,566 15,089 14,900 654,314 Resource solutions 55,965 1,277 1,548 3,651 95,664 Corporate entities — — 387 (386) 251,698 Eliminations — (50,971) — — — $ 215,875 $ — $ 24,337 $ 21,946 $ 1,227,833 Three Months Ended June 30, 2020 Segment Outside Inter-company Depreciation and Operating Total Eastern $ 53,336 $ 13,837 $ 6,339 $ 4,366 $ 211,441 Western 87,286 29,020 13,615 11,863 626,329 Resource solutions 48,145 2,448 1,538 1,801 91,907 Corporate entities — — 584 (586) 37,294 Eliminations — (45,305) — — — $ 188,767 $ — $ 22,076 $ 17,444 $ 966,971 Six Months Ended June 30, 2021 Segment Outside Inter-company Depreciation and Operating Total assets Eastern $ 113,403 $ 28,554 $ 13,935 $ 6,027 $ 226,157 Western 184,616 62,248 29,128 22,657 654,314 Resource solutions 107,387 3,180 3,116 6,113 95,664 Corporate entities — — 840 (842) 251,698 Eliminations — (93,982) — — — Total $ 405,406 $ — $ 47,019 $ 33,955 $ 1,227,833 Six Months Ended June 30, 2020 Segment Outside Inter-company Depreciation and Operating Total assets Eastern $ 103,479 $ 25,676 $ 12,297 $ 5,341 $ 211,441 Western 172,491 54,567 26,847 17,505 626,329 Resource solutions 95,706 5,341 3,148 2,804 91,907 Corporate entities — — 1,190 (1,194) 37,294 Eliminations — (85,584) — — — Total $ 371,676 $ — $ 43,482 $ 24,456 $ 966,971 A summary of our revenues attributable to services provided follows: Three Months Ended Six Months Ended 2021 2020 2021 2020 Collection $ 107,327 $ 94,008 $ 204,796 $ 188,568 Disposal 49,173 43,746 87,026 82,371 Power generation 1,100 918 2,403 1,944 Processing 2,310 1,950 3,794 3,087 Solid waste operations 159,910 140,622 298,019 275,970 Processing 21,031 16,205 38,302 30,023 Non-processing 34,934 31,940 69,085 65,683 Resource solutions operations 55,965 48,145 107,387 95,706 Total revenues $ 215,875 $ 188,767 $ 405,406 $ 371,676

ACCOUNTING CHANGES (Policies)

ACCOUNTING CHANGES (Policies)	6 Months Ended
	Jun. 30, 2021
Accounting Changes and Error Corrections [Abstract]
Basis of Accounting	Casella Waste Systems, Inc. (“Parent”), and its subsidiaries (collectively, “we”, “us” or “our”), is a regional, vertically integrated solid waste services company that provides collection, transfer, disposal, landfill, landfill gas-to-energy, recycling and organics services in the northeastern United States. We market recyclable metals, aluminum, plastics, paper, and corrugated cardboard, which have been processed at our recycling facilities or purchased from third-parties. We manage our solid waste operations on a geographic basis through two regional operating segments, the Eastern and Western regions, each of which provides a full range of solid waste services. We manage our resource-renewal operations through the Resource Solutions operating segment, which includes our larger-scale recycling and commodity brokerage operations along with our organics services and large scale commercial and industrial services. Legal, tax, information technology, human resources, certain finance and accounting and other administrative functions are included in our Corporate Entities segment. The accompanying unaudited consolidated financial statements, which include the accounts of the Parent and our wholly-owned subsidiaries, have been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”) pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”). All significant intercompany accounts and transactions are eliminated in consolidation. Investments in entities in which we do not have a controlling financial interest are accounted for under either the equity method or the cost method of accounting, as appropriate. Our significant accounting policies are more fully discussed in Item 8 of our Annual Report on Form 10-K for the fiscal year ended December 31, 2020 ("fiscal year 2020"), which was filed with the SEC on February 19, 2021.
Use of Estimates	Preparation of our consolidated financial statements in accordance with GAAP requires management to make certain estimates and assumptions. These estimates and assumptions affect the accounting for and recognition and disclosure of assets, liabilities, equity, revenues and expenses. We must make these estimates and assumptions because certain information that we use is dependent on future events, cannot be calculated with a high degree of precision given the available data, or simply cannot be readily calculated. In the opinion of management, these consolidated financial statements include all adjustments, which include normal recurring and nonrecurring adjustments, necessary for a fair presentation of the financial position, results of operations and cash flows for the periods presented. The results for the three and six months ended June 30, 2021 may not be indicative of the results for any other interim period or the entire fiscal year.
Subsequent Events	We have evaluated subsequent events or transactions that have occurred after the consolidated balance sheet date of June 30, 2021 through the date of filing of the consolidated financial statements with the SEC on this Quarterly Report on Form 10-Q. We have determined, except as disclosed, that there are no subsequent events that require disclosure in this Quarterly Report on Form 10-Q.
Accounting Standards Adopted and Pending Adoption	Standard Description Effect on the Financial Statements or Other Accounting standards adopted effective January 1, 2021 ASU No. 2019-12: Income Taxes (Topic 740) Reduces the complexity over accounting for income taxes by removing certain exceptions and amending guidance to improve consistent application of accounting over income taxes. This guidance did not have a material impact on our consolidated financial statements and related disclosures upon adoption, but may in the future. This guidance was effective January 1, 2021. A table providing a brief description of recent ASUs to the ASC issued by the FASB that are pending adoption and deemed to have a possible material impact on our consolidated financial statements based on current account balances and activity follows: Standard Description Effect on the Financial Statements or Other Accounting standards issued pending adoption ASU No. 2020-04: Reference Rate Reform (Topic 848), as amended through January 2021 Provides temporary optional guidance to ease the potential burden in applying GAAP to contract modifications and hedging relationships that reference London Inter-Bank Offered Rate ("LIBOR") or another reference rate expected to be discontinued, subject to meeting certain criteria. We currently have interest rate derivative agreements with hedging relationships that reference LIBOR which extend past the fiscal year ended December 31, 2021. We are currently assessing the provisions of this guidance as LIBOR is still in place and do not expect that its adoption will have a material impact on our consolidated financial statements and related disclosures. This guidance will be in effect from March 12, 2020 through December 31, 2022.
Accrued Final Capping, Closure and Post Closure	Accrued final capping, closure and post-closure costs include the current and non-current portion of costs associated with obligations for final capping, closure and post-closure of our landfills. We estimate our future final capping, closure and post-closure costs in order to determine the final capping, closure and post-closure expense per ton of waste placed into each landfill. The anticipated time frame for paying these costs varies based on the remaining useful life of each landfill as well as the duration of the post-closure monitoring period.
Fair Value of Financial Instruments	We use a three-tier fair value hierarchy to classify and disclose all assets and liabilities measured at fair value on a recurring basis, as well as assets and liabilities measured at fair value on a non-recurring basis, in periods subsequent to their initial measurement. These tiers include: Level 1, defined as quoted market prices in active markets for identical assets or liabilities; Level 2, defined as inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities; and Level 3, defined as unobservable inputs that are not corroborated by market data. We use valuation techniques that maximize the use of market prices and observable inputs and minimize the use of unobservable inputs. In measuring the fair value of our financial assets and liabilities, we rely on market data or assumptions that we believe market participants would use in pricing an asset or a liability.
Segment Reporting	We report selected information about our reportable operating segments in a manner consistent with that used for internal management reporting. We classify our solid waste operations on a geographic basis through regional operating segments, our Western and Eastern regions. Revenues associated with our solid waste operations are derived mainly from solid waste collection and disposal, landfill, landfill gas-to-energy, processing, transfer and recycling services in the northeastern United States. Effective January 1, 2021, we reorganized the Resource Solutions operating segment, which includes our larger-scale recycling and commodity brokerage operations along with our organics services and large scale commercial and industrial services, from our historical lines-of-service of recycling, organics and customer solutions into two lines-of-service: processing and non-processing. Revenues from processing services are derived from municipalities and customers in the form of processing fees, tipping fees, commodity sales, and organic material sales. Revenues from non-processing services are derived from brokerage services; overall resource management services providing a wide range of environmental services and zero waste solutions to large and complex organizations; and traditional collection, disposal and recycling services provided to large account multi-site customers. Revenues classification by service line reported in the three and six months ended June 30, 2020 has been reclassified to conform with the presentation for the three and six months ended June 30, 2021. Legal, tax, information technology, human resources, certain finance and accounting and other administrative functions are included in our Corporate Entities segment.

ACCOUNTING CHANGES (Tables)

ACCOUNTING CHANGES (Tables)	6 Months Ended
	Jun. 30, 2021
Accounting Changes and Error Corrections [Abstract]
Schedule of New Accounting Pronouncements and Changes in Accounting Principles	A table providing a brief description of recent Accounting Standards Updates ("ASUs") to the Accounting Standards Codification (“ASC”) issued by the Financial Accounting Standards Board (“FASB”) that we adopted and deemed to have a material impact on our consolidated financial statements, or a possible material impact in the future, based on current account balances and activity follows: Standard Description Effect on the Financial Statements or Other Accounting standards adopted effective January 1, 2021 ASU No. 2019-12: Income Taxes (Topic 740) Reduces the complexity over accounting for income taxes by removing certain exceptions and amending guidance to improve consistent application of accounting over income taxes. This guidance did not have a material impact on our consolidated financial statements and related disclosures upon adoption, but may in the future. This guidance was effective January 1, 2021. A table providing a brief description of recent ASUs to the ASC issued by the FASB that are pending adoption and deemed to have a possible material impact on our consolidated financial statements based on current account balances and activity follows: Standard Description Effect on the Financial Statements or Other Accounting standards issued pending adoption ASU No. 2020-04: Reference Rate Reform (Topic 848), as amended through January 2021 Provides temporary optional guidance to ease the potential burden in applying GAAP to contract modifications and hedging relationships that reference London Inter-Bank Offered Rate ("LIBOR") or another reference rate expected to be discontinued, subject to meeting certain criteria. We currently have interest rate derivative agreements with hedging relationships that reference LIBOR which extend past the fiscal year ended December 31, 2021. We are currently assessing the provisions of this guidance as LIBOR is still in place and do not expect that its adoption will have a material impact on our consolidated financial statements and related disclosures. This guidance will be in effect from March 12, 2020 through December 31, 2022.

REVENUE RECOGNITION (Tables)

REVENUE RECOGNITION (Tables)	6 Months Ended
	Jun. 30, 2021
Revenue from Contract with Customer [Abstract]
Schedule of Disaggregation of Revenue	A table of revenues disaggregated by service line and timing of revenue recognition by operating segment for each of the three and six months ended June 30, 2021 and 2020 follows: Three Months Ended June 30, 2021 Eastern Western Resource Solutions Total Revenues Collection $ 39,364 $ 67,963 $ — $ 107,327 Landfill 6,118 16,517 — 22,635 Transfer 13,475 9,976 — 23,451 Transportation 47 3,040 — 3,087 Landfill gas-to-energy 246 854 — 1,100 Processing 1,808 502 21,031 23,341 Non-processing — — 34,934 34,934 Total revenues $ 61,058 $ 98,852 $ 55,965 $ 215,875 Transferred at a point-in-time $ 38 $ 487 $ 14,944 $ 15,469 Transferred over time 61,020 98,365 41,021 200,406 Total revenues $ 61,058 $ 98,852 $ 55,965 $ 215,875 Three Months Ended June 30, 2020 Eastern Western Resource Solutions Total Revenues Collection $ 35,463 $ 58,545 $ — $ 94,008 Landfill 4,568 15,218 — 19,786 Transfer 11,451 9,003 — 20,454 Transportation 52 3,454 — 3,506 Landfill gas-to-energy 197 721 — 918 Processing 1,605 345 16,205 18,155 Non-processing — — 31,940 31,940 Total revenues $ 53,336 $ 87,286 $ 48,145 $ 188,767 Transferred at a point-in-time $ 69 $ 367 $ 8,231 $ 8,667 Transferred over time 53,267 86,919 39,914 180,100 Total revenues $ 53,336 $ 87,286 $ 48,145 $ 188,767 Six Months Ended June 30, 2021 Eastern Western Resource Solutions Total Revenues Collection $ 75,440 $ 129,356 $ — $ 204,796 Landfill 11,520 30,136 — 41,656 Transfer 22,899 17,123 — 40,022 Transportation 95 5,253 — 5,348 Landfill gas-to-energy 515 1,888 — 2,403 Processing 2,934 860 38,302 42,096 Non-processing — — 69,085 69,085 Total revenues $ 113,403 $ 184,616 $ 107,387 $ 405,406 Transferred at a point-in-time $ 82 $ 988 $ 25,036 $ 26,106 Transferred over time 113,321 183,628 82,351 379,300 Total revenues $ 113,403 $ 184,616 $ 107,387 $ 405,406 Six Months Ended June 30, 2020 Eastern Western Resource Solutions Total Revenues Collection $ 71,400 $ 117,168 $ — $ 188,568 Landfill 8,112 31,528 — 39,640 Transfer 20,834 15,673 — 36,507 Transportation 99 6,125 — 6,224 Landfill gas-to-energy 583 1,361 — 1,944 Processing 2,451 636 30,023 33,110 Non-processing — — 65,683 65,683 Total revenues $ 103,479 $ 172,491 $ 95,706 $ 371,676 Transferred at a point-in-time $ 125 $ 602 $ 12,692 $ 13,419 Transferred over time 103,354 171,889 83,014 358,257 Total revenues $ 103,479 $ 172,491 $ 95,706 $ 371,676

BUSINESS COMBINATIONS (Tables)

BUSINESS COMBINATIONS (Tables)	6 Months Ended
	Jun. 30, 2021
Business Combination and Asset Acquisition [Abstract]
Summary of Purchase Price Paid for Acquisitions	A summary of the purchase price paid and the purchase price allocation for these acquisitions follows: Six Months Ended 2021 2020 Purchase Price: Cash used in acquisitions, net of cash acquired $ 4,378 $ 19,212 Holdbacks 505 2,837 Total 4,883 22,049 Allocated as follows: Current assets 13 132 Land — 685 Buildings — 2,118 Equipment 1,549 8,277 Intangible assets 1,646 5,912 Other liabilities, net (82) (222) Fair value of assets acquired and liabilities assumed 3,126 16,902 Excess purchase price allocated to goodwill $ 1,757 $ 5,147
Schedule of Unaudited Pro forma Combined Information	Unaudited pro forma combined information that shows our operational results as though each acquisition completed since the beginning of the prior fiscal year had occurred as of January 1, 2020 is as follows: Three Months Ended Six Months Ended 2021 2020 2021 2020 Revenues $ 216,082 $ 192,610 $ 406,242 $ 380,791 Operating income $ 21,955 $ 17,629 $ 34,019 $ 24,880 Net income $ 11,787 $ 12,181 $ 16,129 $ 13,220 Basic earnings per share attributable to common stockholders: Weighted average common shares outstanding 51,366 48,348 51,273 48,176 Basic earnings per common share $ 0.23 $ 0.25 $ 0.31 $ 0.27 Diluted earnings per share attributable to common stockholders: Weighted average common shares outstanding 51,546 48,563 51,466 48,411 Diluted earnings per common share $ 0.23 $ 0.25 $ 0.31 $ 0.27

GOODWILL AND INTANGIBLE ASSETS

GOODWILL AND INTANGIBLE ASSETS (Tables)	6 Months Ended
	Jun. 30, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Summary of Goodwill Activity	A summary of the activity and balances related to goodwill by reporting segment is as follows: December 31, Acquisitions June 30, Eastern region $ 30,873 $ 46 $ 30,919 Western region 149,984 1,739 151,723 Resource solutions 14,044 — 14,044 Total $ 194,901 $ 1,785 $ 196,686
Summary of Intangible Assets by Type	Summaries of intangible assets by type follows: Covenants Client Lists Total Balance, June 30, 2021 Intangible assets $ 27,390 $ 80,036 $ 107,426 Less accumulated amortization (21,323) (30,176) (51,499) $ 6,067 $ 49,860 $ 55,927 Covenants Client Lists Total Balance, December 31, 2020 Intangible assets $ 26,971 $ 78,809 $ 105,780 Less accumulated amortization (20,547) (26,909) (47,456) $ 6,424 $ 51,900 $ 58,324
Summary of Intangible Amortization Expense Estimated	A summary of intangible amortization expense estimated for the five fiscal years following fiscal year 2020 and thereafter follows: Estimated Future Amortization Expense as of June 30, 2021 Fiscal year ending December 31, 2021 $ 4,038 Fiscal year ending December 31, 2022 $ 7,440 Fiscal year ending December 31, 2023 $ 7,183 Fiscal year ending December 31, 2024 $ 8,098 Fiscal year ending December 31, 2025 $ 8,301 Thereafter $ 20,867

ACCRUED FINAL CAPPING, CLOSUR_2

ACCRUED FINAL CAPPING, CLOSURE AND POST CLOSURE (Tables)	6 Months Ended
	Jun. 30, 2021
Asset Retirement Obligation Disclosure [Abstract]
Summary of Changes to Accrued Capping, Closure and Post-Closure Liabilities	A summary of the changes to accrued final capping, closure and post-closure liabilities follows: Six Months Ended 2021 2020 Beginning balance $ 82,533 $ 71,927 Obligations incurred 2,319 1,764 Revision in estimates (1) — 152 Accretion expense 3,676 3,204 Obligations settled (2) (2,969) (1,650) Ending balance $ 85,559 $ 75,397 (1) Relates to changes in estimated costs and timing of final capping, closure and post-closure activities at the Town of Southbridge, Massachusetts landfill. See Note 8, Commitments and Contingencies and Note 11, Other Items and Charges for further discussion. (2) May include amounts that are being processed through accounts payable as a part of our disbursements cycle.

DEBT (Tables)

DEBT (Tables)	6 Months Ended
	Jun. 30, 2021
Debt And Derivatives Disclosure [Abstract]
Summary of Debt	A summary of debt is as follows: June 30, December 31, Senior Secured Credit Facility: Revolving line of credit facility ("Revolving Credit Facility") due May 2023; bearing interest at LIBOR plus 1.50% $ — $ — Term loan A facility ("Term Loan Facility") due May 2023; bearing interest at LIBOR plus 1.50% 348,250 350,000 Tax-Exempt Bonds: New York State Environmental Facilities Corporation Solid Waste Disposal Revenue Bonds Series 2014 ("New York Bonds 2014R-1") due December 2044 - fixed rate interest period through 2029; bearing interest at 2.875% 25,000 25,000 New York State Environmental Facilities Corporation Solid Waste Disposal Revenue Bonds Series 2014R-2 ("New York Bonds 2014R-2") due December 2044 - fixed rate interest period through 2026; bearing interest at 3.125% 15,000 15,000 New York State Environmental Facilities Corporation Solid Waste Disposal Revenue Bonds Series 2020 ("New York Bonds 2020") due September 2050 - fixed rate interest period through 2025; bearing interest at 2.750% 40,000 40,000 Finance Authority of Maine Solid Waste Disposal Revenue Bonds Series 2005R-3 ("FAME Bonds 2005R-3") due January 2025 - fixed rate interest period through 2025; bearing interest at 5.25% 25,000 25,000 Finance Authority of Maine Solid Waste Disposal Revenue Bonds Series 2015R-1 ("FAME Bonds 2015R-1") due August 2035 - fixed rate interest period through 2025; bearing interest at 5.125% 15,000 15,000 Finance Authority of Maine Solid Waste Disposal Revenue Bonds Series 2015R-2 ("FAME Bonds 2015R-2") due August 2035 - fixed rate interest period through 2025; bearing interest at 4.375% 15,000 15,000 Vermont Economic Development Authority Solid Waste Disposal Long-Term Revenue Bonds Series 2013 ("Vermont Bonds") due April 2036 - fixed rate interest period through 2028; bearing interest at 4.625% 16,000 16,000 Business Finance Authority of the State of New Hampshire Solid Waste Disposal Revenue Bonds Series 2013 ("New Hampshire Bonds") due April 2029 - fixed rate interest period through 2029; bearing interest at 2.95% 11,000 11,000 Other: Finance leases maturing through December 2107; bearing interest at a weighted average of 4.0% 34,467 31,486 Notes payable maturing through June 2027; bearing interest at a weighted average of 3.4% 4,454 4,933 Principal amount of debt 549,171 548,419 Less—unamortized debt issuance costs (1) 7,625 8,768 Debt less unamortized debt issuance costs 541,546 539,651 Less—current maturities of debt 14,716 9,240 $ 526,830 $ 530,411 (1) A summary of unamortized debt issuance costs by debt instrument follows: June 30, December 31, Revolving Credit Facility and Term Loan Facility (collectively, the "Credit Facility") $ 3,019 $ 3,839 New York Bonds 2014R-1 967 1,000 New York Bonds 2014R-2 298 329 New York Bonds 2020 1,372 1,461 FAME Bonds 2005R-3 305 347 FAME Bonds 2015R-1 452 482 FAME Bonds 2015R-2 304 343 Vermont Bonds 460 487 New Hampshire Bonds 448 480 $ 7,625 $ 8,768
Summary of Cash Flow Hedges	A summary of the effect of cash flow hedges related to derivative instruments on the consolidated balance sheet follows: Fair Value Balance Sheet Location June 30, December 31, Interest rate swaps Other non-current assets $ 153 $ — Interest rate swaps Other accrued liabilities $ 4,776 $ 4,774 Interest rate swaps Other long-term liabilities 3,959 8,463 $ 8,735 $ 13,237 Interest rate swaps Accumulated other comprehensive loss, net of tax $ (8,782) $ (13,434) Interest rate swaps - tax effect Accumulated other comprehensive loss, net of tax 860 1,917 $ (7,922) $ (11,517) A summary of the amount of expense on cash flow hedging relationships related to interest rate swaps reclassified from accumulated other comprehensive loss into earnings follows: Three Months Ended Six Months Ended Statement of Operations Location 2021 2020 2021 2020 Interest expense $ 1,202 $ 990 $ 2,347 $ 1,357

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Tables)	6 Months Ended
	Jun. 30, 2021
Commitments and Contingencies Disclosure [Abstract]
Summary of Environmental Liability	A summary of the changes to the environmental remediation liability associated with the Southbridge Landfill follows: Six Months Ended 2021 2020 Beginning balance $ 4,261 $ 4,596 Accretion expense 56 62 Obligations incurred — 28 Revision in estimates (1) — (188) Obligations settled (2) (281) (293) Ending balance $ 4,036 $ 4,205 (1) The revision in estimates is associated with the completion of the environmental remediation at the site. See Note 11, Other Items and Charges to our consolidated financial statements for further discussion. (2) May include amounts that are being processed through accounts payable as a part of our disbursements cycle.

STOCKHOLDERS' EQUITY (Tables)

STOCKHOLDERS' EQUITY (Tables)	6 Months Ended
	Jun. 30, 2021
Equity [Abstract]
Summary of Stock Option Activity	A summary of stock option activity follows: Stock Options Weighted Average Exercise Price Weighted Average Remaining Contractual Term (years) Aggregate Intrinsic Value Outstanding, December 31, 2020 90 $ 8.91 Granted — $ — Exercised (9) $ 12.48 Forfeited — $ — Outstanding, June 30, 2021 81 $ 8.51 4.1 $ 4,455 Exercisable, June 30, 2021 81 $ 8.51 4.1 $ 4,455
Summary of Restricted Stock, Restricted Stock Unit and Performance Stock Unit Activity	A summary of restricted stock, restricted stock unit and performance stock unit activity follows: Restricted Stock, Restricted Stock Units, and Performance Stock Units (1) Weighted Weighted Average Remaining Contractual Term (years) Aggregate Intrinsic Value Outstanding, December 31, 2020 307 $ 41.55 Granted 101 $ 67.36 Class A Common Stock Vested (81) $ 35.28 Forfeited (8) $ 51.31 Outstanding, June 30, 2021 319 $ 51.10 1.9 $ 20,233 Unvested, June 30, 2021 584 $ 51.01 1.7 $ 37,062 (1) Market-based performance stock unit grants are included at the 100% attainment level. Attainment of the maximum performance targets and market achievements would result in the issuance of an additional 265 shares of Class A common stock currently included in unvested.
Summary of Changes in Balances of Each Component of Accumulated Other Comprehensive Loss	A summary of the changes in the balances of each component of accumulated other comprehensive loss, net of tax follows: Interest Rate Swaps Balance, December 31, 2020 $ (11,517) Other comprehensive income before reclassifications 2,305 Amounts reclassified from accumulated other comprehensive loss 2,347 Income tax provision related to items of other comprehensive income (1,057) Net current-period other comprehensive income 3,595 Balance, June 30, 2021 $ (7,922)
Summary of Reclassifications Out of Accumulated Other Comprehensive Loss	A summary of reclassifications out of accumulated other comprehensive loss, net of tax follows: Three Months Ended Six Months Ended 2021 2020 2021 2020 Details About Accumulated Other Comprehensive Loss Components Amounts Reclassified Out of Accumulated Other Comprehensive Loss Affected Line Item in the Consolidated Interest rate swaps $ 1,202 $ 990 $ 2,347 $ 1,357 Interest expense (1,202) (990) (2,347) (1,357) Income before income taxes (142) — (269) 112 Provision for income taxes $ (1,060) $ (990) $ (2,078) $ (1,469) Net income

EARNINGS PER SHARE (Tables)

EARNINGS PER SHARE (Tables)	6 Months Ended
	Jun. 30, 2021
Earnings Per Share [Abstract]
Summary of Earnings per Share Computation	A summary of the numerator and denominators used in the computation of earnings per share follows: Three Months Ended Six Months Ended 2021 2020 2021 2020 Numerator: Net income $ 11,783 $ 12,113 $ 16,094 $ 13,072 Denominators: Number of shares outstanding, end of period: Class A common stock 50,398 47,382 50,398 47,382 Class B common stock 988 988 988 988 Unvested restricted stock (2) (1) (2) (1) Effect of weighted average shares outstanding (18) (21) (111) (193) Basic weighted average common shares outstanding 51,366 48,348 51,273 48,176 Impact of potentially dilutive securities: Dilutive effect of stock options and other stock awards 180 215 193 235 Diluted weighted average common shares outstanding 51,546 48,563 51,466 48,411 Anti-dilutive potentially issuable shares — 12 48 12

FAIR VALUE OF FINANCIAL INSTR_2

FAIR VALUE OF FINANCIAL INSTRUMENTS (Tables)	6 Months Ended
	Jun. 30, 2021
Fair Value Disclosures [Abstract]
Summary of Financial Assets and Liabilities Measured at Fair Value	Summaries of our financial assets and liabilities that are measured at fair value on a recurring basis follow: Fair Value Measurement at June 30, 2021 Using: Quoted Prices in Significant Other Significant Assets: Restricted investment securities - landfill closure $ 1,953 $ — $ — Interest rate swaps — 153 — $ 1,953 $ 153 $ — Liabilities: Interest rate swaps $ — $ 8,735 $ — Fair Value Measurement at December 31, 2020 Using: Quoted Prices in Significant Other Significant Assets: Restricted investment securities - landfill closure $ 1,848 $ — $ — Liabilities: Interest rate swaps $ — $ 13,237 $ —

SEGMENT REPORTING (Tables)

SEGMENT REPORTING (Tables)	6 Months Ended
	Jun. 30, 2021
Segment Reporting [Abstract]
Summary of Segment Reporting Information by Segment	Three Months Ended June 30, 2021 Segment Outside Inter-company Depreciation and Operating Total Eastern $ 61,058 $ 16,128 $ 7,313 $ 3,781 $ 226,157 Western 98,852 33,566 15,089 14,900 654,314 Resource solutions 55,965 1,277 1,548 3,651 95,664 Corporate entities — — 387 (386) 251,698 Eliminations — (50,971) — — — $ 215,875 $ — $ 24,337 $ 21,946 $ 1,227,833 Three Months Ended June 30, 2020 Segment Outside Inter-company Depreciation and Operating Total Eastern $ 53,336 $ 13,837 $ 6,339 $ 4,366 $ 211,441 Western 87,286 29,020 13,615 11,863 626,329 Resource solutions 48,145 2,448 1,538 1,801 91,907 Corporate entities — — 584 (586) 37,294 Eliminations — (45,305) — — — $ 188,767 $ — $ 22,076 $ 17,444 $ 966,971 Six Months Ended June 30, 2021 Segment Outside Inter-company Depreciation and Operating Total assets Eastern $ 113,403 $ 28,554 $ 13,935 $ 6,027 $ 226,157 Western 184,616 62,248 29,128 22,657 654,314 Resource solutions 107,387 3,180 3,116 6,113 95,664 Corporate entities — — 840 (842) 251,698 Eliminations — (93,982) — — — Total $ 405,406 $ — $ 47,019 $ 33,955 $ 1,227,833 Six Months Ended June 30, 2020 Segment Outside Inter-company Depreciation and Operating Total assets Eastern $ 103,479 $ 25,676 $ 12,297 $ 5,341 $ 211,441 Western 172,491 54,567 26,847 17,505 626,329 Resource solutions 95,706 5,341 3,148 2,804 91,907 Corporate entities — — 1,190 (1,194) 37,294 Eliminations — (85,584) — — — Total $ 371,676 $ — $ 43,482 $ 24,456 $ 966,971
Summary of Revenue Attributable to Services	A summary of our revenues attributable to services provided follows: Three Months Ended Six Months Ended 2021 2020 2021 2020 Collection $ 107,327 $ 94,008 $ 204,796 $ 188,568 Disposal 49,173 43,746 87,026 82,371 Power generation 1,100 918 2,403 1,944 Processing 2,310 1,950 3,794 3,087 Solid waste operations 159,910 140,622 298,019 275,970 Processing 21,031 16,205 38,302 30,023 Non-processing 34,934 31,940 69,085 65,683 Resource solutions operations 55,965 48,145 107,387 95,706 Total revenues $ 215,875 $ 188,767 $ 405,406 $ 371,676

BASIS OF PRESENTATION (Details)

BASIS OF PRESENTATION (Details)	6 Months Ended
	Jun. 30, 2021regionalOperatingSegment
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of regional operating segments	2

REVENUE RECOGNITION - Disaggreg

REVENUE RECOGNITION - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Total revenues	$ 215,875	$ 188,767	$ 405,406	$ 371,676
Collection
Disaggregation of Revenue [Line Items]
Total revenues	107,327	94,008	204,796	188,568
Landfill
Disaggregation of Revenue [Line Items]
Total revenues	22,635	19,786	41,656	39,640
Transfer
Disaggregation of Revenue [Line Items]
Total revenues	23,451	20,454	40,022	36,507
Transportation
Disaggregation of Revenue [Line Items]
Total revenues	3,087	3,506	5,348	6,224
Landfill gas-to-energy
Disaggregation of Revenue [Line Items]
Total revenues	1,100	918	2,403	1,944
Processing
Disaggregation of Revenue [Line Items]
Total revenues	23,341	18,155	42,096	33,110
Non-processing
Disaggregation of Revenue [Line Items]
Total revenues	34,934	31,940	69,085	65,683
Transferred at a point-in-time
Disaggregation of Revenue [Line Items]
Total revenues	15,469	8,667	26,106	13,419
Transferred over time
Disaggregation of Revenue [Line Items]
Total revenues	200,406	180,100	379,300	358,257
Eastern
Disaggregation of Revenue [Line Items]
Total revenues	61,058	53,336	113,403	103,479
Eastern | Collection
Disaggregation of Revenue [Line Items]
Total revenues	39,364	35,463	75,440	71,400
Eastern | Landfill
Disaggregation of Revenue [Line Items]
Total revenues	6,118	4,568	11,520	8,112
Eastern | Transfer
Disaggregation of Revenue [Line Items]
Total revenues	13,475	11,451	22,899	20,834
Eastern | Transportation
Disaggregation of Revenue [Line Items]
Total revenues	47	52	95	99
Eastern | Landfill gas-to-energy
Disaggregation of Revenue [Line Items]
Total revenues	246	197	515	583
Eastern | Processing
Disaggregation of Revenue [Line Items]
Total revenues	1,808	1,605	2,934	2,451
Eastern | Non-processing
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Eastern | Transferred at a point-in-time
Disaggregation of Revenue [Line Items]
Total revenues	38	69	82	125
Eastern | Transferred over time
Disaggregation of Revenue [Line Items]
Total revenues	61,020	53,267	113,321	103,354
Western
Disaggregation of Revenue [Line Items]
Total revenues	98,852	87,286	184,616	172,491
Western | Collection
Disaggregation of Revenue [Line Items]
Total revenues	67,963	58,545	129,356	117,168
Western | Landfill
Disaggregation of Revenue [Line Items]
Total revenues	16,517	15,218	30,136	31,528
Western | Transfer
Disaggregation of Revenue [Line Items]
Total revenues	9,976	9,003	17,123	15,673
Western | Transportation
Disaggregation of Revenue [Line Items]
Total revenues	3,040	3,454	5,253	6,125
Western | Landfill gas-to-energy
Disaggregation of Revenue [Line Items]
Total revenues	854	721	1,888	1,361
Western | Processing
Disaggregation of Revenue [Line Items]
Total revenues	502	345	860	636
Western | Non-processing
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Western | Transferred at a point-in-time
Disaggregation of Revenue [Line Items]
Total revenues	487	367	988	602
Western | Transferred over time
Disaggregation of Revenue [Line Items]
Total revenues	98,365	86,919	183,628	171,889
Resource solutions
Disaggregation of Revenue [Line Items]
Total revenues	55,965	48,145	107,387	95,706
Resource solutions | Collection
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Resource solutions | Landfill
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Resource solutions | Transfer
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Resource solutions | Transportation
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Resource solutions | Landfill gas-to-energy
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Resource solutions | Processing
Disaggregation of Revenue [Line Items]
Total revenues	21,031	16,205	38,302	30,023
Resource solutions | Non-processing
Disaggregation of Revenue [Line Items]
Total revenues	34,934	31,940	69,085	65,683
Resource solutions | Transferred at a point-in-time
Disaggregation of Revenue [Line Items]
Total revenues	14,944	8,231	25,036	12,692
Resource solutions | Transferred over time
Disaggregation of Revenue [Line Items]
Total revenues	$ 41,021	$ 39,914	$ 82,351	$ 83,014

REVENUE RECOGNITION - Narrative

REVENUE RECOGNITION - Narrative (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Rebates	$ (215,875,000)	$ (188,767,000)	$ (405,406,000)	$ (371,676,000)
Revenue recognized fro performance obligation satisfied in previous period	0	0	0	0
Gross receivables from contracts	79,712,000		79,712,000		$ 74,162,000
Contract liabilities	3,133,000		3,133,000		$ 2,685,000
Rebate for Recycled or Returned Organic Materials
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Rebates	$ 2,532,000	$ 1,546,000	$ 4,100,000	$ 2,537,000

BUSINESS COMBINATIONS - Narrati

BUSINESS COMBINATIONS - Narrative (Details) - business	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Business Acquisition [Line Items]
Number of businesses acquired		4
Minimum
Business Acquisition [Line Items]
Useful life of finite lived intangible assets	5 years
Maximum
Business Acquisition [Line Items]
Useful life of finite lived intangible assets	10 years
Western | Tuck-in Solid Waste Collection Business
Business Acquisition [Line Items]
Number of businesses acquired	2	3
Eastern | Septic and Portable Toilet Business
Business Acquisition [Line Items]
Number of businesses acquired	1
Resource solutions | Recycling Operation
Business Acquisition [Line Items]
Number of businesses acquired		1

BUSINESS COMBINATIONS - Summary

BUSINESS COMBINATIONS - Summary of Purchase Price Paid for Acquisitions (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Purchase Price:
Cash used in acquisitions, net of cash acquired	$ 5,481	$ 20,091
Allocated as follows:
Excess purchase price allocated to goodwill	196,686		$ 194,901
Waste Collection Acquisitions
Purchase Price:
Cash used in acquisitions, net of cash acquired	4,378	19,212
Holdbacks	505	2,837
Total	4,883	22,049
Allocated as follows:
Current assets	13	132
Land	0	685
Buildings	0	2,118
Equipment	1,549	8,277
Intangible assets	1,646	5,912
Other liabilities, net	(82)	(222)
Fair value of assets acquired and liabilities assumed	3,126	16,902
Excess purchase price allocated to goodwill	$ 1,757	$ 5,147

BUSINESS COMBINATIONS - Schedul

BUSINESS COMBINATIONS - Schedule of Unaudited Pro forma Combined Information (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Business Combination and Asset Acquisition [Abstract]
Revenues	$ 216,082	$ 192,610	$ 406,242	$ 380,791
Operating income	21,955	17,629	34,019	24,880
Net income	$ 11,787	$ 12,181	$ 16,129	$ 13,220
Weighted average common shares outstanding, basic	51,366	48,348	51,273	48,176
Basic earnings per common share (in dollars per share)	$ 0.23	$ 0.25	$ 0.31	$ 0.27
Weighted average common shares outstanding, diluted	51,546	48,563	51,466	48,411
Diluted earnings per common share (in dollars per share)	$ 0.23	$ 0.25	$ 0.31	$ 0.27

GOODWILL AND INTANGIBLE ASSET_2

GOODWILL AND INTANGIBLE ASSETS - Summary of Goodwill Activity (Detail) $ in Thousands	6 Months Ended
	Jun. 30, 2021USD ($)
Goodwill [Roll Forward]
Goodwill, beginning balance	$ 194,901
Acquisitions	1,785
Goodwill, ending balance	196,686
Eastern
Goodwill [Roll Forward]
Goodwill, beginning balance	30,873
Acquisitions	46
Goodwill, ending balance	30,919
Western
Goodwill [Roll Forward]
Goodwill, beginning balance	149,984
Acquisitions	1,739
Goodwill, ending balance	151,723
Resource solutions
Goodwill [Roll Forward]
Goodwill, beginning balance	14,044
Acquisitions	0
Goodwill, ending balance	$ 14,044

GOODWILL AND INTANGIBLE ASSET_3

GOODWILL AND INTANGIBLE ASSETS - Summary of Intangible Assets by Type (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Finite-Lived Intangible Assets [Line Items]
Intangible assets	$ 107,426	$ 105,780
Less accumulated amortization	(51,499)	(47,456)
Intangible assets, net	55,927	58,324
Covenants Not-to-Compete
Finite-Lived Intangible Assets [Line Items]
Intangible assets	27,390	26,971
Less accumulated amortization	(21,323)	(20,547)
Intangible assets, net	6,067	6,424
Client Lists
Finite-Lived Intangible Assets [Line Items]
Intangible assets	80,036	78,809
Less accumulated amortization	(30,176)	(26,909)
Intangible assets, net	$ 49,860	$ 51,900

GOODWILL AND INTANGIBLE ASSET_4

GOODWILL AND INTANGIBLE ASSETS - Narrative (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible amortization expense	$ 2,015	$ 2,222	$ 4,043	$ 4,316

GOODWILL AND INTANGIBLE ASSET_5

GOODWILL AND INTANGIBLE ASSETS - Summary of Intangible Amortization Expense Estimated (Detail) $ in Thousands	Jun. 30, 2021USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
Fiscal year ending December 31, 2021	$ 4,038
Fiscal year ending December 31, 2022	7,440
Fiscal year ending December 31, 2023	7,183
Fiscal year ending December 31, 2024	8,098
Fiscal year ending December 31, 2025	8,301
Thereafter	$ 20,867

ACCRUED FINAL CAPPING, CLOSUR_3

ACCRUED FINAL CAPPING, CLOSURE AND POST CLOSURE - Summary of Changes to Accrued Capping, Closure and Post-Closure Liabilities (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	$ 82,533	$ 71,927
Obligations incurred	2,319	1,764
Revision in estimates	0	152
Accretion expense	3,676	3,204
Obligations settled	(2,969)	(1,650)
Ending balance	$ 85,559	$ 75,397

DEBT - Summary of Debt (Details

DEBT - Summary of Debt (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Weighted-average discount rate - finance leases	4.00%
Finance leases maturing through December 2107; bearing interest at a weighted average of 4.0%	$ 34,467	$ 31,486
Principal amount of debt	549,171	548,419
Less - unamortized debt issuance costs	7,625	8,768
Debt less unamortized debt issuance costs	541,546	539,651
Less—current maturities of debt	14,716	9,240
Debt, less current portion	526,830	530,411
Revolving line of credit facility ("Revolving Credit Facility") due May 2023; bearing interest at LIBOR plus 1.50%
Debt Instrument [Line Items]
Principal amount of debt	$ 0	0
Revolving line of credit facility ("Revolving Credit Facility") due May 2023; bearing interest at LIBOR plus 1.50% | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate	1.50%
Secured Debt | Term loan A facility ("Term Loan Facility") due May 2023; bearing interest at LIBOR plus 1.50%
Debt Instrument [Line Items]
Principal amount of debt	$ 348,250	350,000
Secured Debt | Term loan A facility ("Term Loan Facility") due May 2023; bearing interest at LIBOR plus 1.50% | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate	1.50%
Credit Facility
Debt Instrument [Line Items]
Less - unamortized debt issuance costs	$ 3,019	3,839
Unsecured Debt | New York State Environmental Facilities Corporation Solid Waste Disposal Revenue Bonds Series 2014 ("New York Bonds 2014R-1") due December 2044 - fixed rate interest period through 2029; bearing interest at 2.875%
Debt Instrument [Line Items]
Stated interest rate	2.875%
Principal amount of debt	$ 25,000	25,000
Less - unamortized debt issuance costs	$ 967	1,000
Unsecured Debt | New York State Environmental Facilities Corporation Solid Waste Disposal Revenue Bonds Series 2014R-2 ("New York Bonds 2014R-2") due December 2044 - fixed rate interest period through 2026; bearing interest at 3.125%
Debt Instrument [Line Items]
Stated interest rate	3.125%
Principal amount of debt	$ 15,000	15,000
Less - unamortized debt issuance costs	$ 298	329
Unsecured Debt | New York State Environmental Facilities Corporation Solid Waste Disposal Revenue Bonds Series 2020 ("New York Bonds 2020") due September 2050 - fixed rate interest period through 2025; bearing interest at 2.750%
Debt Instrument [Line Items]
Stated interest rate	2.75%
Principal amount of debt	$ 40,000	40,000
Less - unamortized debt issuance costs	$ 1,372	1,461
Unsecured Debt | Finance Authority of Maine Solid Waste Disposal Revenue Bonds Series 2005R-3 ("FAME Bonds 2005R-3") due January 2025 - fixed rate interest period through 2025; bearing interest at 5.25%
Debt Instrument [Line Items]
Stated interest rate	5.25%
Principal amount of debt	$ 25,000	25,000
Less - unamortized debt issuance costs	$ 305	347
Unsecured Debt | Finance Authority of Maine Solid Waste Disposal Revenue Bonds Series 2015R-1 ("FAME Bonds 2015R-1") due August 2035 - fixed rate interest period through 2025; bearing interest at 5.125%
Debt Instrument [Line Items]
Stated interest rate	5.125%
Principal amount of debt	$ 15,000	15,000
Less - unamortized debt issuance costs	$ 452	482
Unsecured Debt | Finance Authority of Maine Solid Waste Disposal Revenue Bonds Series 2015R-2 ("FAME Bonds 2015R-2") due August 2035 - fixed rate interest period through 2025; bearing interest at 4.375%
Debt Instrument [Line Items]
Stated interest rate	4.375%
Principal amount of debt	$ 15,000	15,000
Less - unamortized debt issuance costs	$ 304	343
Unsecured Debt | Vermont Economic Development Authority Solid Waste Disposal Long-Term Revenue Bonds Series 2013 ("Vermont Bonds") due April 2036 - fixed rate interest period through 2028; bearing interest at 4.625%
Debt Instrument [Line Items]
Stated interest rate	4.625%
Principal amount of debt	$ 16,000	16,000
Less - unamortized debt issuance costs	$ 460	487
Unsecured Debt | Business Finance Authority of the State of New Hampshire Solid Waste Disposal Revenue Bonds Series 2013 ("New Hampshire Bonds") due April 2029 - fixed rate interest period through 2029; bearing interest at 2.95%
Debt Instrument [Line Items]
Stated interest rate	2.95%
Principal amount of debt	$ 11,000	11,000
Less - unamortized debt issuance costs	$ 448	480
Notes payable maturing through June 2027; bearing interest at a weighted average of 3.4%
Debt Instrument [Line Items]
Weighted average interest rate	3.40%
Principal amount of debt	$ 4,454	$ 4,933

DEBT - Credit Facility Narrativ

DEBT - Credit Facility Narrative (Details)	6 Months Ended
	Jun. 30, 2021USD ($)
Debt Instrument [Line Items]
Additional borrowing capacity	$ 125,000,000
Line of Credit
Debt Instrument [Line Items]
Debt instrument, term	5 years
Net leverage ratio	2.25
Line of credit facility, remaining borrowing capacity	$ 173,575,000
Line of Credit | LIBOR | Maximum
Debt Instrument [Line Items]
Floor interest rate received	1.50%
Line of Credit | LIBOR | Minimum
Debt Instrument [Line Items]
Floor interest rate received	1.25%
Secured Debt | Term Loan Facility | Line of Credit
Debt Instrument [Line Items]
Aggregate principal amount	$ 350,000,000
Revolving Credit Facility | Revolving Credit Facility Due 2023 | Line of Credit
Debt Instrument [Line Items]
Credit facility maximum	200,000,000
Letters of credit outstanding	$ 26,425,000

DEBT - Cash Flow Hedges Narrati

DEBT - Cash Flow Hedges Narrative (Details) - Cash Flow Hedging - USD ($)	Jun. 30, 2021	Dec. 31, 2020
Interest Rate Derivative
Debt Instrument [Line Items]
Notional amount	$ 195,000,000	$ 190,000,000
Weighted average percentage rate paid	2.51%	2.51%
Forward Starting Interest Rate Derivative
Debt Instrument [Line Items]
Notional amount	$ 85,000,000	$ 125,000,000
Weighted average percentage rate paid	1.55%
Floor interest rate	0.00%

DEBT - Summary of Cash Flow Hed

DEBT - Summary of Cash Flow Hedges (Details) - Designated as Hedging Instrument - Interest rate swaps - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2021	Dec. 31, 2020
Derivatives, Fair Value [Line Items]
Cash flow hedge derivatives, gross liability	$ 8,735	$ 13,237
Other non-current assets
Derivatives, Fair Value [Line Items]
Cash flow hedge derivatives, gross asset	153	0
Other accrued liabilities
Derivatives, Fair Value [Line Items]
Cash flow hedge derivatives, gross liability	4,776	4,774
Other long-term liabilities
Derivatives, Fair Value [Line Items]
Cash flow hedge derivatives, gross liability	3,959	8,463
Accumulated other comprehensive loss, net of tax
Derivatives, Fair Value [Line Items]
Accumulated other comprehensive loss, interest rate swaps	(8,782)	(13,434)
Accumulated other comprehensive loss, interest rate swaps, tax provision	860	1,917
Accumulated other comprehensive loss, net of tax	$ (7,922)	$ (11,517)

DEBT - Schedule of Loss On Cash

DEBT - Schedule of Loss On Cash Flow Hedges (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Derivative Instruments, Gain (Loss) [Line Items]
Other comprehensive loss, reclassification adjustment from AOCI	$ 1,202	$ 990	$ 2,347	$ 1,357
Interest rate swaps | Interest expense
Derivative Instruments, Gain (Loss) [Line Items]
Other comprehensive loss, reclassification adjustment from AOCI	$ 1,202	$ 990	$ 2,347	$ 1,357

COMMITMENTS AND CONTINGENCIES -

COMMITMENTS AND CONTINGENCIES - Narrative (Detail) plantiff in Thousands, $ in Thousands

Dec. 01, 2020USD ($)

Sep. 17, 2019plantiff

Apr. 28, 2017USD ($)

Jun. 30, 2021USD ($)

Dec. 31, 2020USD ($)

Jun. 30, 2020USD ($)

Dec. 31, 2019USD ($)

Apr. 26, 2017USD ($)

Jan. 29, 2016

Apr. 30, 2011USD ($)

May 31, 2009USD ($)

Dec. 20, 2000a

Southbridge Landfill

Loss Contingencies [Line Items]

Risk free interest percentage rate

2.60%

Environmental remediation liability

$ 4,036

$ 4,261

$ 4,205

$ 4,596

Potsdam Environmental Remediation

Loss Contingencies [Line Items]

Risk free interest percentage rate

1.90%

Scrap yard and solid waste transfer station (in acres) | a

25

Undiscounted costs preferred remedies

$ 12,130

$ 10,219

Remediation activities, participant share percentage

15.00%

Environmental remediation liability

$ 939

$ 939

21E Settlement and Water System Construction Funding Agreement | Bonds

Loss Contingencies [Line Items]

Bond period

20 years

21E Settlement and Water System Construction Funding Agreement | Bonds | Maximum

Loss Contingencies [Line Items]

Anticipated cost

$ 4,089

Notice of Intent to Sue under the Resource Conservation and Recovery Act

Loss Contingencies [Line Items]

Estimate of possible loss

$ 5,000

Notice of Intent to Sue under the Resource Conservation and Recovery Act | MADEP and Casella Waste Systems

Loss Contingencies [Line Items]

Estimate of possible loss

$ 10,000

Ontario County, New York Class Action Litigation

Loss Contingencies [Line Items]

Estimate of possible loss

$ 900

Number of citizens seeking damages | plantiff

1

Loss contingency, settlement awarded

$ 750

COMMITMENTS AND CONTINGENCIES_2

COMMITMENTS AND CONTINGENCIES - Environmental Remediation Liability (Details) - Southbridge Landfill - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning balance	$ 4,261	$ 4,596
Accretion expense	56	62
Obligations incurred	0	28
Revision in estimates	0	(188)
Obligations settled	(281)	(293)
Ending balance	$ 4,036	$ 4,205

STOCKHOLDERS' EQUITY - Narrativ

STOCKHOLDERS' EQUITY - Narrative (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Limited Partners' Capital Account [Line Items]
Unrecognized stock-based compensation expense, stock options	$ 0		$ 0
Fair value of stock awards vested	887,000		5,292,000
Stock Options
Limited Partners' Capital Account [Line Items]
Stock-based compensation expense	0	$ 0	0	$ 0
Aggregate intrinsic value of options exercised	448,000		448,000
Restricted Stock, Restricted Stock Units And Performance Stock Units
Limited Partners' Capital Account [Line Items]
Stock-based compensation expense	3,044,000	1,763,000	5,928,000	3,277,000
Restricted Stock
Limited Partners' Capital Account [Line Items]
Unrecognized stock-based compensation expense	108,000		$ 108,000
Restricted Stock | Non Employee Director
Limited Partners' Capital Account [Line Items]
Options, vesting period			3 years
Restricted Stock Unit
Limited Partners' Capital Account [Line Items]
Unrecognized stock-based compensation expense	5,315,000		$ 5,315,000
Performance Stock Unit
Limited Partners' Capital Account [Line Items]
Unrecognized stock-based compensation expense	9,006,000		$ 9,006,000
Weighted average | Restricted Stock
Limited Partners' Capital Account [Line Items]
Unrecognized stock-based compensation, weighted average period			2 years 3 months 18 days
Weighted average | Restricted Stock Unit
Limited Partners' Capital Account [Line Items]
Unrecognized stock-based compensation, weighted average period			1 year 10 months 24 days
Weighted average | Performance Stock Unit
Limited Partners' Capital Account [Line Items]
Unrecognized stock-based compensation, weighted average period			1 year 10 months 24 days
2016 Plan
Limited Partners' Capital Account [Line Items]
Options granted, term			10 years
2016 Plan | Minimum
Limited Partners' Capital Account [Line Items]
Options, vesting period			1 year
2016 Plan | Maximum
Limited Partners' Capital Account [Line Items]
Options, vesting period			4 years
Amended and Restated 1997 Employee Stock Purchase Plan
Limited Partners' Capital Account [Line Items]
Stock-based compensation expense	$ 72,000	$ 56,000	$ 128,000	$ 103,000
Class A Common Stock | 2016 Plan
Limited Partners' Capital Account [Line Items]
Common stock, authorized shares	2,250,000		2,250,000
Number of shares available for future grant	947,000		947,000
Class A Common Stock | 2006 Incentive Plan
Limited Partners' Capital Account [Line Items]
Common stock, additional authorized shares			2,723,000

STOCKHOLDERS' EQUITY - Summary

STOCKHOLDERS' EQUITY - Summary of Stock Option Activity (Detail) $ / shares in Units, shares in Thousands, $ in Thousands	6 Months Ended
	Jun. 30, 2021USD ($)$ / sharesshares
Stock Options
Beginning balance, outstanding (in shares) | shares	90
Granted (in shares) | shares	0
Exercised (in shares) | shares	(9)
Forfeited (in shares) | shares	0
Ending balance, outstanding (in shares) | shares	81
Exercisable at end of period (in shares) | shares	81
Weighted Average Exercise Price
Beginning balance, outstanding (in dollars per share) | $ / shares	$ 8.91
Granted (in dollars per share) | $ / shares	0
Exercised (in dollars per share) | $ / shares	12.48
Forfeited (in dollars per share) | $ / shares	0
Ending balance, outstanding (in dollars per share) | $ / shares	8.51
Exercisable at end of period (in dollars per share) | $ / shares	$ 8.51
Weighted Average Remaining Contractual Term (years) and Aggregate Intrinsic Value
Outstanding contractual term	4 years 1 month 6 days
Exercisable contractual term	4 years 1 month 6 days
Outstanding aggregate intrinsic value | $	$ 4,455
Exercisable aggregate intrinsic value | $	$ 4,455

STOCKHOLDERS' EQUITY - Summar_2

STOCKHOLDERS' EQUITY - Summary of Restricted Stock, Restricted Stock Unit and Performance-based Stock Unit Activity (Detail) $ / shares in Units, shares in Thousands, $ in Thousands	6 Months Ended
	Jun. 30, 2021USD ($)$ / sharesshares
Restricted Stock, Restricted Stock Units And Performance Stock Units
Restricted Stock, Restricted Stock Units, and Performance Stock Units
Outstanding, beginning of period (in shares)	307
Granted (in shares)	101
Forfeited (in shares)	(8)
Outstanding, end of period (in shares)	319
Weighted Average Grant Date Fair Value
Outstanding at beginning of period (in dollars per share) | $ / shares	$ 41.55
Granted (in dollars per share) | $ / shares	67.36
Forfeited (in dollars per share) | $ / shares	51.31
Outstanding at end of period (in dollars per share) | $ / shares	$ 51.10
Weighted Average Remaining Contractual Term (years) and Aggregate Intrinsic Value
Contractual term	1 year 10 months 24 days
Aggregate intrinsic value | $	$ 20,233
Restricted Stock, Restricted Stock Units And Performance Stock Units | Class A Common Stock
Restricted Stock, Restricted Stock Units, and Performance Stock Units
Vested (in shares)	(81)
Weighted Average Grant Date Fair Value
Class A Common Stock Vested (in dollars per share) | $ / shares	$ 35.28
Performance Stock Unit
Weighted Average Remaining Contractual Term (years) and Aggregate Intrinsic Value
Percentage of attainment level	100.00%
Performance Stock Unit | Class A Common Stock
Weighted Average Remaining Contractual Term (years) and Aggregate Intrinsic Value
Number of additional shares	265
Unvested | Restricted Stock, Restricted Stock Units And Performance Stock Units
Restricted Stock, Restricted Stock Units, and Performance Stock Units
Outstanding, end of period (in shares)	584
Weighted Average Grant Date Fair Value
Outstanding at end of period (in dollars per share) | $ / shares	$ 51.01
Weighted Average Remaining Contractual Term (years) and Aggregate Intrinsic Value
Contractual term	1 year 8 months 12 days
Aggregate intrinsic value | $	$ 37,062

STOCKHOLDERS' EQUITY - Summar_3

STOCKHOLDERS' EQUITY - Summary of Changes in Balances of Each Component of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	$ 373,336	$ 362,142	$ 117,996	$ 122,753	$ 362,142	$ 122,753
Other comprehensive (loss) income, net of tax	(235)	3,830	(1,569)	(7,189)	3,595	(8,758)
Ending balance	388,492	373,336	$ 130,745	$ 117,996	388,492	$ 130,745
Accumulated Gain (Loss), Cash Flow Hedge
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance		$ (11,517)			(11,517)
Other comprehensive income					2,305
Amounts reclassified from accumulated other comprehensive loss					2,347
Income tax provision related to items of other comprehensive income					(1,057)
Other comprehensive (loss) income, net of tax					3,595
Ending balance	$ (7,922)				$ (7,922)

STOCKHOLDERS' EQUITY - Summar_4

STOCKHOLDERS' EQUITY - Summary of Reclassifications Out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest expense	$ 5,296		$ 5,511		$ 10,764	$ 11,463
Income before income taxes	17,226		12,470		23,969	13,538
Provision for income taxes	5,443		357		7,875	466
Net income	11,783	$ 4,311	12,113	$ 959	16,094	13,072
Accumulated Gain (Loss), Cash Flow Hedge | Amounts Reclassified Out of Accumulated Other Comprehensive Loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income before income taxes	(1,202)		(990)		(2,347)	(1,357)
Provision for income taxes	(142)		0		(269)	112
Net income	(1,060)		(990)		(2,078)	(1,469)
Interest rate swaps | Accumulated Gain (Loss), Cash Flow Hedge | Amounts Reclassified Out of Accumulated Other Comprehensive Loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest expense	$ 1,202		$ 990		$ 2,347	$ 1,357

EARNINGS PER SHARE (Details)

EARNINGS PER SHARE (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Numerator:
Net income	$ 11,783	$ 12,113	$ 16,094	$ 13,072
Denominators:
Unvested restricted stock (in shares)	(2,000)	(1,000)	(2,000)	(1,000)
Effect of weighted average shares outstanding (in shares)	(18,000)	(21,000)	(111,000)	(193,000)
Weighted average common shares outstanding, basic	51,366,000	48,348,000	51,273,000	48,176,000
Impact of potentially dilutive securities:
Dilutive effect of stock options and other stock awards (in shares)	180,000	215,000	193,000	235,000
Weighted average common shares outstanding, diluted	51,546,000	48,563,000	51,466,000	48,411,000
Anti-dilutive potentially issuable shares	0	12,000	48,000	12,000
Class A Common Stock
Denominators:
Common stock, shares outstanding	50,398,000	47,382,000	50,398,000	47,382,000	50,101,000
Class B Common Stock
Denominators:
Common stock, shares outstanding	988,000	988,000	988,000	988,000	988,000

OTHER ITEMS AND CHARGES (Detail

OTHER ITEMS AND CHARGES (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Site Contingency [Line Items]
Expense from acquisition activities	$ 1,632	$ 352	$ 2,046	$ 1,360
Southbridge Landfill closure charge	195	559	352	1,172
Southbridge Landfill
Site Contingency [Line Items]
Southbridge Landfill closure charge	$ 195	559	$ 352	1,172
Legal and other costs		595		1,208
Amortization		152		152
Recovery credited to environmental remediation expense		$ (188)		$ (188)

FAIR VALUE OF FINANCIAL INSTR_3

FAIR VALUE OF FINANCIAL INSTRUMENTS - Recurring Fair Value Measurements (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Assets:
Restricted investment securities - landfill closure	$ 1,953	$ 1,848
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Interest rate swaps	0
Total assets	1,953
Liabilities:
Interest rate swaps	0	0
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Landfill
Assets:
Restricted investment securities - landfill closure	1,953	1,848
Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Interest rate swaps	153
Total assets	153
Liabilities:
Interest rate swaps	8,735	13,237
Recurring | Significant Other Observable Inputs (Level 2) | Landfill
Assets:
Restricted investment securities - landfill closure	0	0
Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Interest rate swaps	0
Total assets	0
Liabilities:
Interest rate swaps	0	0
Recurring | Significant Unobservable Inputs (Level 3) | Landfill
Assets:
Restricted investment securities - landfill closure	$ 0	$ 0

FAIR VALUE OF FINANCIAL INSTR_4

FAIR VALUE OF FINANCIAL INSTRUMENTS - Additional Information (Detail) - USD ($)	Jun. 30, 2021	Dec. 31, 2020
Term Loan Facility | Secured Debt
Debt Instrument [Line Items]
Principal amount of debt	$ 348,250,000	$ 350,000,000
Fair Value | Fixed Rate Bonds
Debt Instrument [Line Items]
Fixed rate debt	179,187,000
Carrying Value
Debt Instrument [Line Items]
Revolving credit facility	0
Carrying Value | Fixed Rate Bonds
Debt Instrument [Line Items]
Fixed rate debt	$ 162,000,000

SEGMENT REPORTING - Summary of

SEGMENT REPORTING - Summary of Financial Information by Reportable Segment (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
Revenues	$ 215,875	$ 188,767	$ 405,406	$ 371,676
Depreciation and amortization	24,337	22,076	47,019	43,482
Operating Income (Loss)	21,946	17,444	33,955	24,456
Total assets	1,227,833	966,971	1,227,833	966,971	$ 1,193,898
Operating | Eastern
Segment Reporting Information [Line Items]
Revenues	61,058	53,336	113,403	103,479
Depreciation and amortization	7,313	6,339	13,935	12,297
Operating Income (Loss)	3,781	4,366	6,027	5,341
Total assets	226,157	211,441	226,157	211,441
Operating | Western
Segment Reporting Information [Line Items]
Revenues	98,852	87,286	184,616	172,491
Depreciation and amortization	15,089	13,615	29,128	26,847
Operating Income (Loss)	14,900	11,863	22,657	17,505
Total assets	654,314	626,329	654,314	626,329
Operating | Resource solutions
Segment Reporting Information [Line Items]
Revenues	55,965	48,145	107,387	95,706
Depreciation and amortization	1,548	1,538	3,116	3,148
Operating Income (Loss)	3,651	1,801	6,113	2,804
Total assets	95,664	91,907	95,664	91,907
Corporate entities
Segment Reporting Information [Line Items]
Revenues	0	0	0	0
Depreciation and amortization	387	584	840	1,190
Operating Income (Loss)	(386)	(586)	(842)	(1,194)
Total assets	251,698	37,294	251,698	37,294
Inter-company revenues
Segment Reporting Information [Line Items]
Revenues	(50,971)	(45,305)	(93,982)	(85,584)
Inter-company revenues | Eastern
Segment Reporting Information [Line Items]
Revenues	(16,128)	(13,837)	(28,554)	(25,676)
Inter-company revenues | Western
Segment Reporting Information [Line Items]
Revenues	(33,566)	(29,020)	(62,248)	(54,567)
Inter-company revenues | Resource solutions
Segment Reporting Information [Line Items]
Revenues	$ (1,277)	$ (2,448)	$ (3,180)	$ (5,341)

SEGMENT REPORTING - Summary o_2

SEGMENT REPORTING - Summary of Revenues Attributable to Services Provided by Company (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Revenue from External Customer [Line Items]
Revenues	$ 215,875	$ 188,767	$ 405,406	$ 371,676
Solid waste operations
Revenue from External Customer [Line Items]
Revenues	159,910	140,622	298,019	275,970
Collection
Revenue from External Customer [Line Items]
Revenues	107,327	94,008	204,796	188,568
Disposal
Revenue from External Customer [Line Items]
Revenues	49,173	43,746	87,026	82,371
Power generation
Revenue from External Customer [Line Items]
Revenues	1,100	918	2,403	1,944
Processing
Revenue from External Customer [Line Items]
Revenues	2,310	1,950	3,794	3,087
Resource solutions operations
Revenue from External Customer [Line Items]
Revenues	55,965	48,145	107,387	95,706
Processing
Revenue from External Customer [Line Items]
Revenues	21,031	16,205	38,302	30,023
Non-processing
Revenue from External Customer [Line Items]
Revenues	$ 34,934	$ 31,940	$ 69,085	$ 65,683

Uncategorized Items - cwst-2021

Label	Element	Value
Accounting Standards Update [Extensible Enumeration]	us-gaap_AccountingStandardsUpdateExtensibleList	Accounting Standards Update 2016-13 [Member]