GUARANTOR AND NON-GUARANTOR SUBSIDIARIES (Cash Flows) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed consolidating statement of cash flows
Net cash from operating activities	$ 285,698	$ 259,624	$ 396,383
Cash flows used in investing activities:
Additions to property, plant and equipment	(167,007)	(219,384)	(257,196)
Proceeds from sale and disposal of fixed assets	7,124	20,817	6,195
Proceeds from sale of investments	376	0	0
Acquisitions, net of cash acquired	(49,227)	(206,915)	(94,345)
Proceeds on sale of businesses, net of transactional costs	45,426	47,134	0
Additions to intangible assets including costs to obtain or renew permits	(1,617)	(2,831)	(5,296)
Purchases of available-for-sale securities	(38,342)	(598)	0
Investment in subsidiaries		0
Intercompany	0	0	0
Intercompany debt	0	0	0
Net cash used in investing activities	(203,267)	(361,777)	(350,642)
Cash flows (used in) from financing activities:
Change in uncashed checks	(5,940)	(3,177)	(14,630)
Proceeds from exercise of stock options	46	627	397
Tax payments related to withholdings on vested restricted stock	(3,149)	(2,819)	(2,159)
Excess tax benefit of stock-based compensation	0	1,198	71
Deferred financing costs paid	(5,718)	(4,031)	0
Repurchases of common stock	(48,971)	(22,188)	(73,347)
Payments on capital leases	0	0	(511)
Principal payment on debt	(402,000)	0	0
Premiums paid on early extinguishment of debt	(6,028)	0	0
Issuance of senior secured notes, net of discount	399,000	0	0
Issuance of senior unsecured notes, including premium	0	250,625	0
Intercompany	0	0	0
Intercompany debt	0	0	0
Net cash (used in) from financing activities	(72,760)	220,235	(90,179)
Effect of exchange rate change on cash	2,731	4,207	(17,733)
Increase (decrease) in cash and cash equivalents	12,402	122,289	(62,171)
Cash and cash equivalents, beginning of year	306,997	184,708	246,879
Cash and cash equivalents, end of year	319,399	306,997	184,708
Guarantor Subsidiaries
Cash flows used in investing activities:
Proceeds from sale of investments	0
Reportable Legal Entities | Clean Harbors, Inc.
Condensed consolidating statement of cash flows
Net cash from operating activities	16,292	51,033	9,543
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 investments	376
Acquisitions, net of cash acquired	0	0	0
Proceeds on 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	(102)
Investment in subsidiaries		(257,125)
Intercompany	0	0	0
Intercompany debt	0	0	0
Net cash used in investing activities	376	(257,227)	0
Cash flows (used in) from financing activities:
Change in uncashed checks	0	0	0
Proceeds from exercise of stock options	46	627	397
Tax payments related to withholdings on vested restricted stock	(3,149)	(2,819)	(2,159)
Excess tax benefit of stock-based compensation		1,198	71
Deferred financing costs paid	(5,718)	(4,031)
Repurchases of common stock	(48,971)	(22,188)	(73,347)
Payments on capital leases			0
Principal payment on debt	(402,000)
Premiums paid on early extinguishment of debt	(6,028)
Issuance of senior secured notes, net of discount	399,000
Issuance of senior unsecured notes, including premium		250,625
Intercompany	54,074	23,182	75,506
Intercompany debt	(3,701)	0	0
Net cash (used in) from financing activities	(16,447)	246,594	468
Effect of exchange rate change on cash	0	0	0
Increase (decrease) in cash and cash equivalents	221	40,400	10,011
Cash and cash equivalents, beginning of year	51,417	11,017	1,006
Cash and cash equivalents, end of year	51,638	51,417	11,017
Reportable Legal Entities | Guarantor Subsidiaries
Condensed consolidating statement of cash flows
Net cash from operating activities	217,001	125,591	314,585
Cash flows used in investing activities:
Additions to property, plant and equipment	(142,211)	(194,184)	(220,789)
Proceeds from sale and disposal of fixed assets	1,979	12,926	1,447
Acquisitions, net of cash acquired	(11,427)	(196,915)	(94,345)
Proceeds on sale of businesses, net of transactional costs	45,245	18,885
Additions to intangible assets including costs to obtain or renew permits	(1,153)	(1,749)	0
Purchases of available-for-sale securities	0	0
Investment in subsidiaries		0
Intercompany	(54,074)	(23,182)	(75,506)
Intercompany debt	0	63,118	14,272
Net cash used in investing activities	(161,641)	(321,101)	(374,921)
Cash flows (used in) from financing activities:
Change in uncashed checks	(3,526)	(3,651)	(10,129)
Proceeds from exercise of stock options	0	0	0
Tax payments related to withholdings on vested restricted stock	0	0	0
Excess tax benefit of stock-based compensation		0	0
Deferred financing costs paid	0	0
Repurchases of common stock	0	0	0
Payments on capital leases			(203)
Principal payment on debt	0
Premiums paid on early extinguishment of debt	0
Issuance of senior secured notes, net of discount	0
Issuance of senior unsecured notes, including premium		250,625
Intercompany	0	0	0
Intercompany debt	0	21,000	0
Net cash (used in) from financing activities	(3,526)	267,974	(10,332)
Effect of exchange rate change on cash	0	0	0
Increase (decrease) in cash and cash equivalents	51,834	72,464	(70,668)
Cash and cash equivalents, beginning of year	155,943	83,479	154,147
Cash and cash equivalents, end of year	207,777	155,943	83,479
Reportable Legal Entities | Non-Guarantor Subsidiaries
Condensed consolidating statement of cash flows
Net cash from operating activities	52,405	83,000	72,255
Cash flows used in investing activities:
Additions to property, plant and equipment	(24,796)	(25,200)	(36,407)
Proceeds from sale and disposal of fixed assets	5,145	7,891	4,748
Proceeds from sale of investments	0
Acquisitions, net of cash acquired	(37,800)	(10,000)	0
Proceeds on sale of businesses, net of transactional costs	181	28,249
Additions to intangible assets including costs to obtain or renew permits	(464)	(1,082)	(5,296)
Purchases of available-for-sale securities	(38,342)	(496)
Investment in subsidiaries		0
Intercompany	0	0	0
Intercompany debt	3,701	(21,000)	0
Net cash used in investing activities	(92,375)	(21,638)	(36,955)
Cash flows (used in) from financing activities:
Change in uncashed checks	(2,414)	474	(4,501)
Proceeds from exercise of stock options	0	0	0
Tax payments related to withholdings on vested restricted stock	0	0	0
Excess tax benefit of stock-based compensation		0	0
Deferred financing costs paid	0	0
Repurchases of common stock	0	0	0
Payments on capital leases			(308)
Principal payment on debt	0
Premiums paid on early extinguishment of debt	0
Issuance of senior secured notes, net of discount	0
Issuance of senior unsecured notes, including premium		0
Intercompany	0	6,500	0
Intercompany debt	0	(63,118)	(14,272)
Net cash (used in) from financing activities	(2,414)	(56,144)	(19,081)
Effect of exchange rate change on cash	2,731	4,207	(17,733)
Increase (decrease) in cash and cash equivalents	(39,653)	9,425	(1,514)
Cash and cash equivalents, beginning of year	99,637	90,212	91,726
Cash and cash equivalents, end of year	59,984	99,637	90,212
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 investments	0
Acquisitions, net of cash acquired	0	0	0
Proceeds on 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
Investment in subsidiaries		257,125
Intercompany	54,074	23,182	75,506
Intercompany debt	(3,701)	(42,118)	(14,272)
Net cash used in investing activities	50,373	238,189	61,234
Cash flows (used in) from financing activities:
Change in uncashed checks	0	0	0
Proceeds from exercise of stock options	0	0	0
Tax payments related to withholdings on vested restricted stock	0	0	0
Excess tax benefit of stock-based compensation		0	0
Deferred financing costs paid	0	0
Repurchases of common stock	0	0	0
Payments on capital leases			0
Principal payment on debt	0
Premiums paid on early extinguishment of debt	0
Issuance of senior secured notes, net of discount	0
Issuance of senior unsecured notes, including premium		(250,625)
Intercompany	(54,074)	(29,682)	(75,506)
Intercompany debt	3,701	42,118	14,272
Net cash (used in) from financing activities	(50,373)	(238,189)	(61,234)
Effect of exchange rate change on cash	0	0	0
Increase (decrease) 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