GUARANTOR AND NON-GUARANTOR SUBSIDIARIES (Balance Sheet) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Assets:
Cash and cash equivalents	$ 226,507	$ 319,399	$ 306,997	$ 184,708
Short-term marketable securities	52,856	38,179
Intercompany receivables	0	0
Accounts receivable, net	606,952	528,924
Other current assets	315,843	267,554
Property, plant and equipment, net	1,561,978	1,587,365
Investments in subsidiaries	0	0
Intercompany debt receivable	0	0
Goodwill	514,189	478,523	465,154
Permits and other intangibles, net	441,875	469,128
Other long-term assets	18,121	17,498
Total assets	3,738,321	3,706,570
Liabilities and Stockholders' Equity:
Current liabilities	602,278	503,817
Intercompany payables	0	0
Closure, post-closure and remedial liabilities, net	167,914	165,723
Long-term obligations, less current portion	1,565,021	1,625,537
Intercompany debt payable	0	0
Other long-term liabilities	233,352	223,291
Total liabilities	2,568,565	2,518,368
Stockholders' equity	1,169,756	1,188,202	1,084,241	1,096,282
Total liabilities and stockholders' equity	3,738,321	3,706,570
Reportable Legal Entities | Clean Harbors, Inc.
Assets:
Cash and cash equivalents	27,308	51,638	51,417	11,017
Short-term marketable securities	67	0
Intercompany receivables	262,475	238,339
Accounts receivable, net	0	0
Other current assets	0	897
Property, plant and equipment, net	0	0
Investments in subsidiaries	3,162,704	3,112,547
Intercompany debt receivable	0	0
Goodwill	0	0
Permits and other intangibles, net	0	0
Other long-term assets	1,551	2,084
Total assets	3,454,105	3,405,505
Liabilities and Stockholders' Equity:
Current liabilities	20,170	16,954
Intercompany payables	699,158	574,812
Closure, post-closure and remedial liabilities, net	0	0
Long-term obligations, less current portion	1,565,021	1,625,537
Intercompany debt payable	0	0
Other long-term liabilities	0	0
Total liabilities	2,284,349	2,217,303
Stockholders' equity	1,169,756	1,188,202
Total liabilities and stockholders' equity	3,454,105	3,405,505
Reportable Legal Entities | Guarantor Subsidiaries
Assets:
Cash and cash equivalents	101,302	207,777	155,943	83,479
Short-term marketable securities	0	0
Intercompany receivables	721,521	590,100
Accounts receivable, net	520,785	433,042
Other current assets	289,869	233,602
Property, plant and equipment, net	1,233,578	1,174,975
Investments in subsidiaries	571,304	569,568
Intercompany debt receivable	14,669	92,530
Goodwill	456,307	415,641
Permits and other intangibles, net	393,045	408,655
Other long-term assets	13,545	12,064
Total assets	4,315,925	4,137,954
Liabilities and Stockholders' Equity:
Current liabilities	457,164	371,135
Intercompany payables	321,846	289,531
Closure, post-closure and remedial liabilities, net	151,480	148,872
Long-term obligations, less current portion	0	0
Intercompany debt payable	21,000	21,000
Other long-term liabilities	212,924	201,086
Total liabilities	1,164,414	1,031,624
Stockholders' equity	3,151,511	3,106,330
Total liabilities and stockholders' equity	4,315,925	4,137,954
Reportable Legal Entities | Non-Guarantor Subsidiaries
Assets:
Cash and cash equivalents	97,897	59,984	99,637	90,212
Short-term marketable securities	52,789	38,179
Intercompany receivables	60,693	52,909
Accounts receivable, net	86,167	95,882
Other current assets	49,631	52,947
Property, plant and equipment, net	328,400	412,390
Investments in subsidiaries	0	0
Intercompany debt receivable	21,000	21,000
Goodwill	57,882	62,882
Permits and other intangibles, net	48,830	60,473
Other long-term assets	3,025	3,350
Total assets	806,314	859,996
Liabilities and Stockholders' Equity:
Current liabilities	148,601	135,620
Intercompany payables	23,685	17,005
Closure, post-closure and remedial liabilities, net	16,434	16,851
Long-term obligations, less current portion	0	0
Intercompany debt payable	14,669	92,530
Other long-term liabilities	20,428	22,205
Total liabilities	223,817	284,211
Stockholders' equity	582,497	575,785
Total liabilities and stockholders' equity	806,314	859,996
Consolidating Adjustments
Assets:
Cash and cash equivalents	0	0	$ 0	$ 0
Short-term marketable securities	0	0
Intercompany receivables	(1,044,689)	(881,348)
Accounts receivable, net	0	0
Other current assets	(23,657)	(19,892)
Property, plant and equipment, net	0	0
Investments in subsidiaries	(3,734,008)	(3,682,115)
Intercompany debt receivable	(35,669)	(113,530)
Goodwill	0	0
Permits and other intangibles, net	0	0
Other long-term assets	0	0
Total assets	(4,838,023)	(4,696,885)
Liabilities and Stockholders' Equity:
Current liabilities	(23,657)	(19,892)
Intercompany payables	(1,044,689)	(881,348)
Closure, post-closure and remedial liabilities, net	0	0
Long-term obligations, less current portion	0	0
Intercompany debt payable	(35,669)	(113,530)
Other long-term liabilities	0	0
Total liabilities	(1,104,015)	(1,014,770)
Stockholders' equity	(3,734,008)	(3,682,115)
Total liabilities and stockholders' equity	$ (4,838,023)	$ (4,696,885)