GUARANTOR AND NON-GUARANTOR SUBSIDIARIES FINANCIAL INFORMATION (Condensed Consolidating Statements of Cash Flows) (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Condensed consolidating statement of cash flows
Net cash from (used in) operating activities	$ 51,903	$ 57,119
Cash flows used in investing activities:
Additions to property, plant and equipment	(44,242)	(42,462)
Proceeds from sale and disposal of fixed assets	798	1,030
Acquisitions, net of cash acquired	(120,000)	(11,946)
Proceeds from sale of business	0	2,018
Additions to intangible assets, including costs to obtain or renew permits	(1,245)	(751)
Proceeds from sale of available-for-sale securities	3,264
Purchases of available-for-sale securities	(3,003)	0
Proceeds from sale of investments		243
Intercompany	0	0
Net cash used in investing activities	(164,428)	(51,868)
Cash flows used in financing activities:
Change in uncashed checks	(3,843)	(7,557)
Proceeds from exercise of stock options	0	46
Tax payments related to withholdings on vested restricted stock	(548)	(1,021)
Repurchases of common stock	(14,264)	(6,796)
Deferred financing costs paid	0	(108)
Principal payment on debt	(1,000)	0
Intercompany	0	0
Net cash used in financing activities	(19,655)	(15,436)
Effect of exchange rate change on cash	(867)	554
Increase (decrease) in cash and cash equivalents	(133,047)	(9,631)
Cash and cash equivalents, beginning of period	319,399	306,997
Cash and cash equivalents, end of period	186,352	297,366
Consolidating Adjustments
Condensed consolidating statement of cash flows
Net cash from (used in) 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		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 investments		0
Intercompany	15,812	7,771
Net cash used in investing activities	15,812	7,771
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
Principal payment on debt	0
Intercompany	(15,812)	(7,771)
Net cash used in financing activities	(15,812)	(7,771)
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.
Cash flows used in investing activities:
Proceeds from sale of investments		243
Clean Harbors, Inc. \| Reportable Legal Entities
Condensed consolidating statement of cash flows
Net cash from (used in) operating activities	143	(1,663)
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		1,837
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
Intercompany	0	0
Net cash used in investing activities	0	2,080
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	(548)	(1,021)
Repurchases of common stock	(14,264)	(6,796)
Deferred financing costs paid		(108)
Principal payment on debt	(1,000)
Intercompany	15,812	7,771
Net cash used in financing activities	0	(108)
Effect of exchange rate change on cash	0	0
Increase (decrease) in cash and cash equivalents	143	309
Cash and cash equivalents, beginning of period	51,638	51,417
Cash and cash equivalents, end of period	51,781	51,726
Guarantor Subsidiaries
Cash flows used in investing activities:
Proceeds from sale of investments		0
Guarantor Subsidiaries \| Reportable Legal Entities
Condensed consolidating statement of cash flows
Net cash from (used in) operating activities	69,536	41,144
Cash flows used in investing activities:
Additions to property, plant and equipment	(37,319)	(33,136)
Proceeds from sale and disposal of fixed assets	292	664
Acquisitions, net of cash acquired	(120,000)	(11,946)
Proceeds from sale of business		0
Additions to intangible assets, including costs to obtain or renew permits	(1,234)	(573)
Proceeds from sale of available-for-sale securities	0
Purchases of available-for-sale securities	0
Intercompany	(15,812)	(7,771)
Net cash used in investing activities	(174,073)	(52,762)
Cash flows used in financing activities:
Change in uncashed checks	(3,578)	(5,165)
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
Principal payment on debt	0
Intercompany	0	0
Net cash used in financing activities	(3,578)	(5,165)
Effect of exchange rate change on cash	0	0
Increase (decrease) in cash and cash equivalents	(108,115)	(16,783)
Cash and cash equivalents, beginning of period	207,777	155,943
Cash and cash equivalents, end of period	99,662	139,160
Non-Guarantor Subsidiaries
Cash flows used in investing activities:
Proceeds from sale of investments		0
Non-Guarantor Subsidiaries \| Reportable Legal Entities
Condensed consolidating statement of cash flows
Net cash from (used in) operating activities	(17,776)	17,638
Cash flows used in investing activities:
Additions to property, plant and equipment	(6,923)	(9,326)
Proceeds from sale and disposal of fixed assets	506	366
Acquisitions, net of cash acquired	0	0
Proceeds from sale of business		181
Additions to intangible assets, including costs to obtain or renew permits	(11)	(178)
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	(6,167)	(8,957)
Cash flows used in financing activities:
Change in uncashed checks	(265)	(2,392)
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
Principal payment on debt	0
Intercompany	0	0
Net cash used in financing activities	(265)	(2,392)
Effect of exchange rate change on cash	(867)	554
Increase (decrease) in cash and cash equivalents	(25,075)	6,843
Cash and cash equivalents, beginning of period	59,984	99,637
Cash and cash equivalents, end of period	$ 34,909	$ 106,480

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