CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities:
Net income (loss)	$ 5,337	$ (389,359)	$ 33,140
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization of property and equipment	70,799	66,561	41,423
Amortization of intangible assets	34,614	37,344	15,491
Accretion of closure and post-closure obligations	5,363	4,000	4,388
Goodwill and intangible asset impairment charges		404,900
Integration-related property and equipment charges		3,067
Property and equipment impairment charges			25
Unrealized foreign currency gain	(1,647)	(1,472)	(666)
Deferred income taxes	(635)	(4,148)	6,601
Share-based compensation expense	7,478	6,651	5,544
Share-based payments of business development and integration expenses	411	1,182	3,717
Unrecognized tax benefits	16	(8)	(238)
Net (gain) loss on disposition of assets	(116)	1,504	426
Gain on insurance proceeds from damaged property and equipment			(12,366)
Amortization and write-off of debt issuance costs	2,440	2,217	1,007
Amortization and write-off of debt discount	161	161	27
Change in fair value of contingent consideration	282	(3,682)	349
Change in fair value of minority interest investment	(3,509)
Changes in assets and liabilities (net of effects of business acquisition):
Receivables	(14,685)	8,381	(9,357)
Income taxes receivable	3,830	(7,049)	(4,163)
Other assets	(5,271)	(5,443)	(2,163)
Accounts payable and accrued liabilities	15,985	(13,628)	(10,706)
Deferred revenue	658	(1,619)	967
Accrued salaries and benefits	(1,483)	(121)	8,326
Income taxes payable	(430)	(549)	(244)
Closure and post-closure obligations	(3,279)	(1,744)	(1,912)
Net cash provided by operating activities	116,319	107,146	79,616
Cash flows from investing activities:
Purchases of property and equipment	(68,666)	(57,399)	(58,100)
Proceeds from sale of property and equipment	2,431	1,897	1,182
Minority interest investment	(712)		(7,870)
Proceeds from sale of short-term investments	2,142
Purchases of restricted investments	(1,017)	(1,615)	(1,197)
Proceeds from sale of restricted investments	1,267	1,483	1,145
Business acquisitions (net of cash acquired)		(3,309)	(399,599)
Insurance proceeds from damaged property and equipment		1,305	12,714
Payment of acquired contingent consideration liabilities			(4,000)
Net cash used in investing activities	(64,555)	(57,638)	(455,725)
Cash flows from financing activities:
Proceeds from short-term borrowings	61,326	72,353	77,997
Payments on short-term borrowings	(61,326)	(72,353)	(77,997)
Payments on long-term debt	(48,500)	(74,500)	(80,000)
Payment of equipment financing obligations	(5,616)	(6,327)	(1,539)
Payment of acquired contingent consideration liabilities	(2,553)	(2,517)
Deferred financing costs paid	(957)	(1,144)	(9,416)
Repurchase of common stock	(465)	(18,332)	(915)
Proceeds from long-term debt		90,000	491,875
Dividends paid		(5,667)	(15,890)
Other		28	319
Net cash (used in) provided by financing activities	(58,091)	(18,459)	384,434
Effect of foreign exchange rate changes on cash	277	1,915	1,062
(Decrease) increase in Cash and cash equivalents and restricted cash	(6,050)	32,964	9,387
Cash and cash equivalents and restricted cash at beginning of year	75,104	42,140	32,753
Cash and cash equivalents and restricted cash at end of year	$ 69,054	$ 75,104	$ 42,140