GUARANTOR AND NON-GUARANTOR SUBSIDIARIES FINANCIAL INFORMATION (Condensed Consolidating Statements of Cash Flows) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Condensed consolidating statement of cash flows
Net cash from operating activities	$ 247,215	$ 221,469
Cash flows used in investing activities:
Additions to property, plant and equipment	(150,722)	(127,736)
Proceeds from sale and disposal of fixed assets	6,111	5,375
Acquisitions, net of cash acquired	(151,023)	(44,432)
Proceeds from sale of business, net of transactional costs	0	46,339
Additions to intangible assets, including costs to obtain or renew permits	(3,500)	(1,348)
Proceeds from sale of available-for-sale securities	20,123
Purchases of available-for-sale securities	(20,471)	0
Proceeds from sale of available-for-sale securities		376
Borrowing from revolving credit facility	50,000	0
Intercompany	0	0
Net cash used in investing activities	(299,482)	(121,426)
Cash flows used in financing activities:
Change in uncashed checks	(3,476)	(8,657)
Proceeds from exercise of stock options	0	46
Tax payments related to withholdings on vested restricted stock	(2,566)	(2,321)
Repurchases of common stock	(33,581)	(24,465)
Deferred financing costs paid	(3,938)	(5,746)
Premiums paid on early extinguishment of debt	(1,219)	(6,028)
Principal payment on debt	(403,884)	(401,000)
Issuance of senior secured notes, net of discount	348,250	399,000
Intercompany	0	0
Intercompany debt		0
Net cash used in financing activities	(50,414)	(49,171)
Effect of exchange rate change on cash	(1,221)	3,789
Increase (decrease) in cash and cash equivalents	(103,902)	54,661
Cash and cash equivalents, beginning of period	319,399	306,997
Cash and cash equivalents, end of period	215,497	361,658
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 business, 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
Borrowing from revolving credit facility	0
Intercompany	40,031	27,740
Intercompany debt		3,701
Net cash used in investing activities	40,031	24,039
Cash flows used in 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	0
Principal payment on debt	0	0
Issuance of senior secured notes, net of discount	0	0
Intercompany	(40,031)	(27,740)
Intercompany debt		3,701
Net cash used in financing activities	(40,031)	(24,039)
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	8,877	16,196
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 business, 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	(1,450)
Proceeds from sale of available-for-sale securities		376
Borrowing from revolving credit facility	50,000
Intercompany	0	0
Intercompany debt		0
Net cash used in investing activities	(1,450)	376
Cash flows used in financing activities:
Change in uncashed checks	0	0
Proceeds from exercise of stock options		46
Tax payments related to withholdings on vested restricted stock	(2,566)	(2,321)
Repurchases of common stock	(33,581)	(24,465)
Deferred financing costs paid	(3,938)	(5,746)
Premiums paid on early extinguishment of debt	(1,219)	(6,028)
Principal payment on debt	(403,884)	(401,000)
Issuance of senior secured notes, net of discount	348,250	399,000
Intercompany	40,031	27,740
Intercompany debt		(3,701)
Net cash used in financing activities	(6,907)	(16,475)
Effect of exchange rate change on cash	0	0
Increase (decrease) in cash and cash equivalents	520	97
Cash and cash equivalents, beginning of period	51,638	51,417
Cash and cash equivalents, end of period	52,158	51,514
Guarantor Subsidiaries | Reportable Legal Entities
Condensed consolidating statement of cash flows
Net cash from operating activities	216,369	169,715
Cash flows used in investing activities:
Additions to property, plant and equipment	(125,098)	(105,564)
Proceeds from sale and disposal of fixed assets	3,788	1,625
Acquisitions, net of cash acquired	(151,023)	(11,427)
Proceeds from sale of business, net of transactional costs		46,158
Additions to intangible assets, including costs to obtain or renew permits	(3,262)	(1,018)
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
Borrowing from revolving credit facility	0
Intercompany	(40,031)	(27,740)
Intercompany debt		0
Net cash used in investing activities	(315,626)	(97,966)
Cash flows used in financing activities:
Change in uncashed checks	(3,002)	(6,140)
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	0
Principal payment on debt	0	0
Issuance of senior secured notes, net of discount	0	0
Intercompany	0	0
Intercompany debt		0
Net cash used in financing activities	(3,002)	(6,140)
Effect of exchange rate change on cash	0	0
Increase (decrease) in cash and cash equivalents	(102,259)	65,609
Cash and cash equivalents, beginning of period	207,777	155,943
Cash and cash equivalents, end of period	105,518	221,552
Non-Guarantor Subsidiaries | Reportable Legal Entities
Condensed consolidating statement of cash flows
Net cash from operating activities	21,969	35,558
Cash flows used in investing activities:
Additions to property, plant and equipment	(25,624)	(22,172)
Proceeds from sale and disposal of fixed assets	2,323	3,750
Acquisitions, net of cash acquired	0	(33,005)
Proceeds from sale of business, net of transactional costs		181
Additions to intangible assets, including costs to obtain or renew permits	(238)	(330)
Proceeds from sale of available-for-sale securities	20,123
Purchases of available-for-sale securities	(19,021)
Proceeds from sale of available-for-sale securities		0
Borrowing from revolving credit facility	0
Intercompany	0	0
Intercompany debt		(3,701)
Net cash used in investing activities	(22,437)	(47,875)
Cash flows used in financing activities:
Change in uncashed checks	(474)	(2,517)
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	0
Principal payment on debt	0	0
Issuance of senior secured notes, net of discount	0	0
Intercompany	0	0
Intercompany debt		0
Net cash used in financing activities	(474)	(2,517)
Effect of exchange rate change on cash	(1,221)	3,789
Increase (decrease) in cash and cash equivalents	(2,163)	(11,045)
Cash and cash equivalents, beginning of period	59,984	99,637
Cash and cash equivalents, end of period	$ 57,821	$ 88,592