GUARANTOR AND NON-GUARANTOR SUBSIDIARIES (Cash Flows) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed consolidating statement of cash flows
Net cash from operating activities	$ 373,210	$ 285,698	$ 259,624
Cash flows used in investing activities:
Additions to property, plant and equipment	(193,344)	(167,007)	(219,384)
Proceeds from sale and disposal of fixed assets	15,445	7,124	20,817
Proceeds from sale of available-for-sale securities	28,723	376
Acquisitions, net of cash acquired	(151,023)	(49,227)	(206,915)
Proceeds from sale of businesses, net of transactional costs	0	45,426	47,134
Additions to intangible assets including costs to obtain or renew permits	(4,688)	(1,617)	(2,831)
Purchases of available-for-sale securities	(44,772)	(38,342)	(598)
Intercompany	0	0	0
Intercompany debt		0	0
Investment in subsidiaries			0
Net cash used in investing activities	(349,659)	(203,267)	(361,777)
Cash flows (used in) from financing activities:
Change in uncashed checks	132	(5,940)	(3,177)
Proceeds from exercise of stock options	0	46	627
Tax payments related to withholdings on vested restricted stock	(3,266)	(3,149)	(2,819)
Excess tax benefit of stock-based compensation	0	0	1,198
Deferred financing costs paid	(4,027)	(5,718)	(4,031)
Repurchases of common stock	(45,080)	(48,971)	(22,188)
Principal payments on debt	(405,768)	(402,000)	0
Premiums paid on early extinguishment of debt	(1,238)	(6,028)	0
Issuance of senior secured notes, net of discount	348,250	399,000	0
Issuance of senior secured notes, net of discount	0	0	250,625
Borrowing from revolving credit facility	50,000	0	0
Payment on revolving credit facility	(50,000)	0	0
Intercompany	0	0	0
Intercompany debt		0	0
Net cash (used in) from financing activities	(110,997)	(72,760)	220,235
Effect of exchange rate change on cash	(5,446)	2,731	4,207
(Decrease) increase in cash and cash equivalents	(92,892)	12,402	122,289
Cash and cash equivalents, beginning of year	319,399	306,997	184,708
Cash and cash equivalents, end of year	226,507	319,399	306,997
Guarantor Subsidiaries
Cash flows used in investing activities:
Proceeds from sale of available-for-sale securities	0
Reportable Legal Entities | Clean Harbors, Inc.
Condensed consolidating statement of cash flows
Net cash from operating activities	34,135	16,292	51,033
Cash flows used in investing activities:
Additions to property, plant and equipment	0	0	0
Proceeds from sale and disposal of fixed assets	0	0	0
Proceeds from sale of available-for-sale securities	0	376
Acquisitions, net of cash acquired	0	0	0
Proceeds from sale of businesses, net of transactional costs		0	0
Additions to intangible assets including costs to obtain or renew permits	0	0	0
Purchases of available-for-sale securities	(1,450)	0	(102)
Intercompany	0	0	0
Intercompany debt		0	0
Investment in subsidiaries			(257,125)
Net cash used in investing activities	(1,450)	376	(257,227)
Cash flows (used in) from financing activities:
Change in uncashed checks	0	0	0
Proceeds from exercise of stock options		46	627
Tax payments related to withholdings on vested restricted stock	(3,266)	(3,149)	(2,819)
Excess tax benefit of stock-based compensation			1,198
Deferred financing costs paid	(4,027)	(5,718)	(4,031)
Repurchases of common stock	(45,080)	(48,971)	(22,188)
Principal payments on debt	(405,768)	(402,000)
Premiums paid on early extinguishment of debt	(1,238)	(6,028)
Issuance of senior secured notes, net of discount	348,250	399,000
Issuance of senior secured notes, net of discount			250,625
Borrowing from revolving credit facility	50,000
Payment on revolving credit facility	(50,000)
Intercompany	54,114	54,074	23,182
Intercompany debt		(3,701)	0
Net cash (used in) from financing activities	(57,015)	(16,447)	246,594
Effect of exchange rate change on cash	0	0	0
(Decrease) increase in cash and cash equivalents	(24,330)	221	40,400
Cash and cash equivalents, beginning of year	51,638	51,417	11,017
Cash and cash equivalents, end of year	27,308	51,638	51,417
Reportable Legal Entities | Guarantor Subsidiaries
Condensed consolidating statement of cash flows
Net cash from operating activities	260,101	217,001	125,591
Cash flows used in investing activities:
Additions to property, plant and equipment	(161,342)	(142,211)	(194,184)
Proceeds from sale and disposal of fixed assets	4,174	1,979	12,926
Proceeds from sale of available-for-sale securities		0
Acquisitions, net of cash acquired	(151,023)	(11,427)	(196,915)
Proceeds from sale of businesses, net of transactional costs		45,245	18,885
Additions to intangible assets including costs to obtain or renew permits	(4,326)	(1,153)	(1,749)
Purchases of available-for-sale securities	0	0	0
Intercompany	(54,114)	(54,074)	(23,182)
Intercompany debt		0	63,118
Investment in subsidiaries			0
Net cash used in investing activities	(366,631)	(161,641)	(321,101)
Cash flows (used in) from financing activities:
Change in uncashed checks	55	(3,526)	(3,651)
Proceeds from exercise of stock options		0	0
Tax payments related to withholdings on vested restricted stock	0	0	0
Excess tax benefit of stock-based compensation			0
Deferred financing costs paid	0	0	0
Repurchases of common stock	0	0	0
Principal payments on debt	0	0
Premiums paid on early extinguishment of debt	0	0
Issuance of senior secured notes, net of discount	0	0
Issuance of senior secured notes, net of discount			250,625
Borrowing from revolving credit facility	0
Payment on revolving credit facility	0
Intercompany	0	0	0
Intercompany debt		0	21,000
Net cash (used in) from financing activities	55	(3,526)	267,974
Effect of exchange rate change on cash	0	0	0
(Decrease) increase in cash and cash equivalents	(106,475)	51,834	72,464
Cash and cash equivalents, beginning of year	207,777	155,943	83,479
Cash and cash equivalents, end of year	101,302	207,777	155,943
Reportable Legal Entities | Non-Guarantor Subsidiaries
Condensed consolidating statement of cash flows
Net cash from operating activities	78,974	52,405	83,000
Cash flows used in investing activities:
Additions to property, plant and equipment	(32,002)	(24,796)	(25,200)
Proceeds from sale and disposal of fixed assets	11,271	5,145	7,891
Proceeds from sale of available-for-sale securities	28,723	0
Acquisitions, net of cash acquired	0	(37,800)	(10,000)
Proceeds from sale of businesses, net of transactional costs		181	28,249
Additions to intangible assets including costs to obtain or renew permits	(362)	(464)	(1,082)
Purchases of available-for-sale securities	(43,322)	(38,342)	(496)
Intercompany	0	0	0
Intercompany debt		3,701	(21,000)
Investment in subsidiaries			0
Net cash used in investing activities	(35,692)	(92,375)	(21,638)
Cash flows (used in) from financing activities:
Change in uncashed checks	77	(2,414)	474
Proceeds from exercise of stock options		0	0
Tax payments related to withholdings on vested restricted stock	0	0	0
Excess tax benefit of stock-based compensation			0
Deferred financing costs paid	0	0	0
Repurchases of common stock	0	0	0
Principal payments on debt	0	0
Premiums paid on early extinguishment of debt	0	0
Issuance of senior secured notes, net of discount	0	0
Issuance of senior secured notes, net of discount			0
Borrowing from revolving credit facility	0
Payment on revolving credit facility	0
Intercompany	0	0	6,500
Intercompany debt		0	(63,118)
Net cash (used in) from financing activities	77	(2,414)	(56,144)
Effect of exchange rate change on cash	(5,446)	2,731	4,207
(Decrease) increase in cash and cash equivalents	37,913	(39,653)	9,425
Cash and cash equivalents, beginning of year	59,984	99,637	90,212
Cash and cash equivalents, end of year	97,897	59,984	99,637
Consolidating Adjustments
Condensed consolidating statement of cash flows
Net cash from operating activities	0	0	0
Cash flows used in investing activities:
Additions to property, plant and equipment	0	0	0
Proceeds from sale and disposal of fixed assets	0	0	0
Proceeds from sale of available-for-sale securities	0	0
Acquisitions, net of cash acquired	0	0	0
Proceeds from sale of businesses, net of transactional costs		0	0
Additions to intangible assets including costs to obtain or renew permits	0	0	0
Purchases of available-for-sale securities	0	0	0
Intercompany	54,114	54,074	23,182
Intercompany debt		(3,701)	(42,118)
Investment in subsidiaries			257,125
Net cash used in investing activities	54,114	50,373	238,189
Cash flows (used in) from financing activities:
Change in uncashed checks	0	0	0
Proceeds from exercise of stock options		0	0
Tax payments related to withholdings on vested restricted stock	0	0	0
Excess tax benefit of stock-based compensation			0
Deferred financing costs paid	0	0	0
Repurchases of common stock	0	0	0
Principal payments on debt	0	0
Premiums paid on early extinguishment of debt	0	0
Issuance of senior secured notes, net of discount	0	0
Issuance of senior secured notes, net of discount			(250,625)
Borrowing from revolving credit facility	0
Payment on revolving credit facility	0
Intercompany	(54,114)	(54,074)	(29,682)
Intercompany debt		3,701	42,118
Net cash (used in) from financing activities	(54,114)	(50,373)	(238,189)
Effect of exchange rate change on cash	0	0	0
(Decrease) increase in cash and cash equivalents	0	0	0
Cash and cash equivalents, beginning of year	0	0	0
Cash and cash equivalents, end of year	$ 0	$ 0	$ 0