CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net income	$ 22,587	$ 20,096
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	58,144	51,572
Operating lease right-of-use assets expense	7,272
Depletion of landfill operating lease obligations		7,827
Interest accretion on landfill and environmental remediation liabilities	5,310	4,291
Amortization of debt issuance costs and discount on long-term debt	1,724	1,875
Stock-based compensation	5,218	6,366
Gain on sale of property and equipment	(806)	(414)
Southbridge Landfill non-cash closure charge	58	1,354
Southbridge Landfill insurance recovery for investing activities	0	(3,506)
Development project charge	0	311
Non-cash expense from acquisition activities and other items	71	211
Loss on debt extinguishment	0	7,352
Withdrawal costs - multiemployer pension plan	3,591	0
Deferred income taxes	(1,267)	79
Changes in assets and liabilities, net of effects of acquisitions and divestitures:
Accounts receivable	(15,141)	(12,161)
Landfill operating lease contract expenditures	(3,197)	0
Accounts payable	1,634	8,009
Prepaid expenses, inventories and other assets	(1,297)	829
Accrued expenses, contract liabilities and other liabilities	(17,986)	(4,174)
Net cash provided by operating activities	71,495	89,917
Cash Flows from Investing Activities:
Acquisitions, net of cash acquired	(73,496)	(58,176)
Additions to property, plant and equipment	(75,998)	(51,841)
Payments on landfill operating lease contracts	0	(5,006)
Proceeds from sale of property and equipment	542	609
Proceeds from property insurance settlement	332	992
Net cash used in investing activities	(148,620)	(109,916)
Cash Flows from Financing Activities:
Proceeds from long-term borrowings	121,500	566,800
Principal payments on long-term debt	(149,774)	(540,611)
Payments of debt issuance costs	0	(5,573)
Proceeds from the exercise of share based awards	3,355	471
Proceeds from the public issuance of Class A Common Stock	100,446	0
Proceeds from unregistered sale of Class A Common Stock	2,619	0
Net cash provided by financing activities	78,146	21,087
Net increase in cash and cash equivalents	1,021	1,088
Cash and cash equivalents, beginning of period	4,007	1,995
Cash and cash equivalents, end of period	5,028	3,083
Cash paid during the period for:
Interest	17,200	16,950
Income taxes, net of refunds	84	84
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Non-current assets obtained through long-term obligations	9,797	4,342
Contingent consideration from business combinations	0	2,924
Landfill
Adjustments to reconcile net income to net cash provided by operating activities:
Operating lease right-of-use assets expense	5,580
Cash Flows from Investing Activities:
Proceeds from property insurance settlement	$ 0	$ 3,506