GUARANTOR AND NON-GUARANTOR SUBSIDIARIES FINANCIAL INFORMATION (Condensed Consolidating Statements of Cash Flows) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Condensed consolidating statement of cash flows
Net cash from operating activities	$ 129,670	$ 116,931
Cash flows used in investing activities:
Additions to property, plant and equipment	(94,139)	(88,742)
Proceeds from sale and disposal of fixed assets	2,641	2,121
Acquisitions, net of cash acquired	(123,750)	(9,277)
Proceeds from sale of businesses, net of transactional costs	0	46,391
Additions to intangible assets, including costs to obtain or renew permits	(2,106)	(1,239)
Proceeds from sale of available-for-sale securities	11,214
Purchases of available-for-sale securities	(10,001)	0
Proceeds from sale of available-for-sale securities		376
Intercompany	0	0
Net cash used in investing activities	(216,141)	(50,370)
Cash flows (used in) from financing activities:
Change in uncashed checks	(2,803)	(8,361)
Proceeds from exercise of stock options	0	46
Tax payments related to withholdings on vested restricted stock	(2,175)	(2,132)
Repurchases of common stock	(26,482)	(12,257)
Deferred financing costs paid	(468)	(4,727)
Premiums paid on early extinguishment of debt	0	(4,665)
Principal payment on debt	(2,000)	(296,202)
Issuance of senior secured notes, net of discount		399,000
Intercompany	0	0
Net cash (used in) from financing activities	(33,928)	70,702
Effect of exchange rate change on cash	(1,932)	2,106
Increase (decrease) in cash and cash equivalents	(122,331)	139,369
Cash and cash equivalents, beginning of period	319,399	306,997
Cash and cash equivalents, end of period	197,068	446,366
Consolidating Adjustments
Condensed consolidating statement of cash flows
Net cash from operating activities	0	0
Cash flows used in investing activities:
Additions to property, plant and equipment	0	0
Proceeds from sale and disposal of fixed assets	0	0
Acquisitions, net of cash acquired	0	0
Proceeds from sale of businesses, net of transactional costs		0
Additions to intangible assets, including costs to obtain or renew permits	0	0
Proceeds from sale of available-for-sale securities	0
Purchases of available-for-sale securities	0
Proceeds from sale of available-for-sale securities		0
Intercompany	30,657	14,343
Net cash used in investing activities	30,657	14,343
Cash flows (used in) from financing activities:
Change in uncashed checks	0	0
Proceeds from exercise of stock options		0
Tax payments related to withholdings on vested restricted stock	0	0
Repurchases of common stock	0	0
Deferred financing costs paid	0	0
Premiums paid on early extinguishment of debt		0
Principal payment on debt	0	0
Issuance of senior secured notes, net of discount		0
Intercompany	(30,657)	(14,343)
Net cash (used in) from financing activities	(30,657)	(14,343)
Effect of exchange rate change on cash	0	0
Increase (decrease) in cash and cash equivalents	0	0
Cash and cash equivalents, beginning of period	0	0
Cash and cash equivalents, end of period	0	0
Clean Harbors, Inc. | Reportable Legal Entities
Condensed consolidating statement of cash flows
Net cash from operating activities	790	(93,808)
Cash flows used in investing activities:
Additions to property, plant and equipment	0	0
Proceeds from sale and disposal of fixed assets	0	0
Acquisitions, net of cash acquired	0	0
Proceeds from sale of businesses, net of transactional costs		0
Additions to intangible assets, including costs to obtain or renew permits	0	0
Proceeds from sale of available-for-sale securities	0
Purchases of available-for-sale securities	0
Proceeds from sale of available-for-sale securities		376
Intercompany	0	0
Net cash used in investing activities	0	376
Cash flows (used in) from financing activities:
Change in uncashed checks	0	0
Proceeds from exercise of stock options		46
Tax payments related to withholdings on vested restricted stock	(2,175)	(2,132)
Repurchases of common stock	(26,482)	(12,257)
Deferred financing costs paid	(468)	(4,727)
Premiums paid on early extinguishment of debt		(4,665)
Principal payment on debt	(2,000)	(296,202)
Issuance of senior secured notes, net of discount		399,000
Intercompany	30,657	14,343
Net cash (used in) from financing activities	(468)	93,406
Effect of exchange rate change on cash	0	0
Increase (decrease) in cash and cash equivalents	322	(26)
Cash and cash equivalents, beginning of period	51,638	51,417
Cash and cash equivalents, end of period	51,960	51,391
Guarantor Subsidiaries | Reportable Legal Entities
Condensed consolidating statement of cash flows
Net cash from operating activities	121,021	206,496
Cash flows used in investing activities:
Additions to property, plant and equipment	(77,773)	(75,152)
Proceeds from sale and disposal of fixed assets	1,035	984
Acquisitions, net of cash acquired	(123,750)	(9,277)
Proceeds from sale of businesses, net of transactional costs		46,210
Additions to intangible assets, including costs to obtain or renew permits	(1,991)	(888)
Proceeds from sale of available-for-sale securities	0
Purchases of available-for-sale securities	0
Proceeds from sale of available-for-sale securities		0
Intercompany	(30,657)	(14,343)
Net cash used in investing activities	(233,136)	(52,466)
Cash flows (used in) from financing activities:
Change in uncashed checks	(2,829)	(5,977)
Proceeds from exercise of stock options		0
Tax payments related to withholdings on vested restricted stock	0	0
Repurchases of common stock	0	0
Deferred financing costs paid	0	0
Premiums paid on early extinguishment of debt		0
Principal payment on debt	0	0
Issuance of senior secured notes, net of discount		0
Intercompany	0	0
Net cash (used in) from financing activities	(2,829)	(5,977)
Effect of exchange rate change on cash	0	0
Increase (decrease) in cash and cash equivalents	(114,944)	148,053
Cash and cash equivalents, beginning of period	207,777	155,943
Cash and cash equivalents, end of period	92,833	303,996
Non-Guarantor Subsidiaries | Reportable Legal Entities
Condensed consolidating statement of cash flows
Net cash from operating activities	7,859	4,243
Cash flows used in investing activities:
Additions to property, plant and equipment	(16,366)	(13,590)
Proceeds from sale and disposal of fixed assets	1,606	1,137
Acquisitions, net of cash acquired	0	0
Proceeds from sale of businesses, net of transactional costs		181
Additions to intangible assets, including costs to obtain or renew permits	(115)	(351)
Proceeds from sale of available-for-sale securities	11,214
Purchases of available-for-sale securities	(10,001)
Proceeds from sale of available-for-sale securities		0
Intercompany	0	0
Net cash used in investing activities	(13,662)	(12,623)
Cash flows (used in) from financing activities:
Change in uncashed checks	26	(2,384)
Proceeds from exercise of stock options		0
Tax payments related to withholdings on vested restricted stock	0	0
Repurchases of common stock	0	0
Deferred financing costs paid	0	0
Premiums paid on early extinguishment of debt		0
Principal payment on debt	0	0
Issuance of senior secured notes, net of discount		0
Intercompany	0	0
Net cash (used in) from financing activities	26	(2,384)
Effect of exchange rate change on cash	(1,932)	2,106
Increase (decrease) in cash and cash equivalents	(7,709)	(8,658)
Cash and cash equivalents, beginning of period	59,984	99,637
Cash and cash equivalents, end of period	$ 52,275	$ 90,979