GUARANTOR AND NON-GUARANTOR SUBSIDIARIES FINANCIAL INFORMATION (Condensed Consolidating Statements of Cash Flows) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Condensed consolidating statement of cash flows
Net cash from operating activities	$ 29,740	$ 51,903
Cash flows used in investing activities:
Additions to property, plant and equipment	(58,947)	(44,242)
Proceeds from sale and disposal of fixed assets	4,321	798
Acquisitions, net of cash acquired	(14,870)	(120,000)
Additions to intangible assets including costs to obtain or renew permits	(1,132)	(1,245)
Proceeds from sale of available-for-sale securities	8,600
Purchases of available-for-sale securities	(12,941)
Proceeds from sale of available-for-sale securities		3,264
Purchases of available-for-sale securities		(3,003)
Intercompany	0	0
Net cash used in investing activities	(74,969)	(164,428)
Cash flows used in financing activities:
Change in uncashed checks	(4,769)	(3,843)
Tax payments related to withholdings on vested restricted stock	(2,276)	(548)
Repurchases of common stock	(6,324)	(14,264)
Payments on finance lease	(115)
Principal payments on debt	(1,884)	(1,000)
Intercompany	0	0
Net cash used in financing activities	(15,368)	(19,655)
Effect of exchange rate change on cash	1,461	(867)
Decrease in cash and cash equivalents	(59,136)	(133,047)
Cash and cash equivalents, beginning of period	226,507	319,399
Cash and cash equivalents, end of period	167,371	186,352
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
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
Purchases of available-for-sale securities		0
Intercompany	10,484	15,812
Net cash used in investing activities	10,484	15,812
Cash flows used in financing activities:
Change in uncashed checks	0	0
Tax payments related to withholdings on vested restricted stock	0	0
Repurchases of common stock	0	0
Payments on finance lease	0
Principal payments on debt	0	0
Intercompany	(10,484)	(15,812)
Net cash used in financing activities	(10,484)	(15,812)
Effect of exchange rate change on cash	0	0
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	123	143
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
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
Purchases of available-for-sale securities		0
Intercompany	0	0
Net cash used in investing activities	0	0
Cash flows used in financing activities:
Change in uncashed checks	0	0
Tax payments related to withholdings on vested restricted stock	(2,276)	(548)
Repurchases of common stock	(6,324)	(14,264)
Payments on finance lease	0
Principal payments on debt	(1,884)	(1,000)
Intercompany	10,484	15,812
Net cash used in financing activities	0	0
Effect of exchange rate change on cash	0	0
Decrease in cash and cash equivalents	123	143
Cash and cash equivalents, beginning of period	27,308	51,638
Cash and cash equivalents, end of period	27,431	51,781
Guarantor Subsidiaries | Reportable Legal Entities
Condensed consolidating statement of cash flows
Net cash from operating activities	50,344	69,536
Cash flows used in investing activities:
Additions to property, plant and equipment	(48,696)	(37,319)
Proceeds from sale and disposal of fixed assets	3,366	292
Acquisitions, net of cash acquired	(14,870)	(120,000)
Additions to intangible assets including costs to obtain or renew permits	(1,294)	(1,234)
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
Purchases of available-for-sale securities		0
Intercompany	(10,484)	(15,812)
Net cash used in investing activities	(71,978)	(174,073)
Cash flows used in financing activities:
Change in uncashed checks	(4,454)	(3,578)
Tax payments related to withholdings on vested restricted stock	0	0
Repurchases of common stock	0	0
Payments on finance lease	(115)
Principal payments on debt	0	0
Intercompany	0	0
Net cash used in financing activities	(4,569)	(3,578)
Effect of exchange rate change on cash	0	0
Decrease in cash and cash equivalents	(26,203)	(108,115)
Cash and cash equivalents, beginning of period	101,302	207,777
Cash and cash equivalents, end of period	75,099	99,662
Non-Guarantor Subsidiaries | Reportable Legal Entities
Condensed consolidating statement of cash flows
Net cash from operating activities	(20,727)	(17,776)
Cash flows used in investing activities:
Additions to property, plant and equipment	(10,251)	(6,923)
Proceeds from sale and disposal of fixed assets	955	506
Acquisitions, net of cash acquired	0	0
Additions to intangible assets including costs to obtain or renew permits	162	(11)
Proceeds from sale of available-for-sale securities	8,600
Purchases of available-for-sale securities	(12,941)
Proceeds from sale of available-for-sale securities		3,264
Purchases of available-for-sale securities		(3,003)
Intercompany	0	0
Net cash used in investing activities	(13,475)	(6,167)
Cash flows used in financing activities:
Change in uncashed checks	(315)	(265)
Tax payments related to withholdings on vested restricted stock	0	0
Repurchases of common stock	0	0
Payments on finance lease	0
Principal payments on debt	0	0
Intercompany	0	0
Net cash used in financing activities	(315)	(265)
Effect of exchange rate change on cash	1,461	(867)
Decrease in cash and cash equivalents	(33,056)	(25,075)
Cash and cash equivalents, beginning of period	97,897	59,984
Cash and cash equivalents, end of period	$ 64,841	$ 34,909