GUARANTOR AND NON-GUARANTOR SUBSIDIARIES FINANCIAL INFORMATION (Condensed Consolidating Balance Sheets) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
ASSETS
Cash and cash equivalents	$ 215,497	$ 319,399	$ 361,658	$ 306,997
Short-term marketable securities	37,380	38,179
Intercompany receivables	0	0
Accounts receivable, net	608,645	528,924
Other current assets	315,299	267,554
Property, plant and equipment, net	1,614,429	1,587,365
Investments in subsidiaries	0	0
Intercompany debt receivable	0	0
Goodwill	514,102	478,523
Permits and other intangibles, net	451,355	469,128
Other long-term assets	17,622	17,498
Total assets	3,774,329	3,706,570
LIABILITIES AND STOCKHOLDERS' EQUITY
Current liabilities	576,300	503,817
Intercompany payables	0	0
Closure, post-closure and remedial liabilities, net	162,837	165,723
Long-term obligations, less current portion	1,616,156	1,625,537
Intercompany debt payable	0	0
Other long-term liabilities	221,712	223,291
Total liabilities	2,577,005	2,518,368
Stockholders’ equity	1,197,324	1,188,202
Total liabilities and stockholders’ equity	3,774,329	3,706,570
Reportable Legal Entities | Clean Harbors, Inc.
ASSETS
Cash and cash equivalents	52,158	51,638	51,514	51,417
Short-term marketable securities	368	0
Intercompany receivables	256,615	238,339
Accounts receivable, net	0	0
Other current assets	0	897
Property, plant and equipment, net	0	0
Investments in subsidiaries	3,185,768	3,112,547
Intercompany debt receivable	0	0
Goodwill	0	0
Permits and other intangibles, net	0	0
Other long-term assets	1,720	2,084
Total assets	3,496,629	3,405,505
LIABILITIES AND STOCKHOLDERS' EQUITY
Current liabilities	22,515	16,954
Intercompany payables	660,634	574,812
Closure, post-closure and remedial liabilities, net	0	0
Long-term obligations, less current portion	1,616,156	1,625,537
Intercompany debt payable	0	0
Other long-term liabilities	0	0
Total liabilities	2,299,305	2,217,303
Stockholders’ equity	1,197,324	1,188,202
Total liabilities and stockholders’ equity	3,496,629	3,405,505
Reportable Legal Entities | Guarantor Subsidiaries
ASSETS
Cash and cash equivalents	105,518	207,777	221,552	155,943
Short-term marketable securities	0	0
Intercompany receivables	667,371	590,100
Accounts receivable, net	511,333	433,042
Other current assets	264,204	233,602
Property, plant and equipment, net	1,251,472	1,174,975
Investments in subsidiaries	599,352	569,568
Intercompany debt receivable	15,491	92,530
Goodwill	453,052	415,641
Permits and other intangibles, net	398,117	408,655
Other long-term assets	13,055	12,064
Total assets	4,278,965	4,137,954
LIABILITIES AND STOCKHOLDERS' EQUITY
Current liabilities	428,273	371,135
Intercompany payables	306,805	289,531
Closure, post-closure and remedial liabilities, net	145,795	148,872
Long-term obligations, less current portion	0	0
Intercompany debt payable	21,000	21,000
Other long-term liabilities	200,278	201,086
Total liabilities	1,102,151	1,031,624
Stockholders’ equity	3,176,814	3,106,330
Total liabilities and stockholders’ equity	4,278,965	4,137,954
Reportable Legal Entities | Non-Guarantor Subsidiaries
ASSETS
Cash and cash equivalents	57,821	59,984	88,592	99,637
Short-term marketable securities	37,012	38,179
Intercompany receivables	51,517	52,909
Accounts receivable, net	97,312	95,882
Other current assets	53,281	52,947
Property, plant and equipment, net	362,957	412,390
Investments in subsidiaries	0	0
Intercompany debt receivable	21,000	21,000
Goodwill	61,050	62,882
Permits and other intangibles, net	53,238	60,473
Other long-term assets	2,844	3,350
Total assets	798,032	859,996
LIABILITIES AND STOCKHOLDERS' EQUITY
Current liabilities	127,698	135,620
Intercompany payables	8,064	17,005
Closure, post-closure and remedial liabilities, net	17,042	16,851
Long-term obligations, less current portion	0	0
Intercompany debt payable	15,491	92,530
Other long-term liabilities	21,431	22,205
Total liabilities	189,726	284,211
Stockholders’ equity	608,306	575,785
Total liabilities and stockholders’ equity	798,032	859,996
Consolidating Adjustments
ASSETS
Cash and cash equivalents	0	0	$ 0	$ 0
Short-term marketable securities	0	0
Intercompany receivables	(975,503)	(881,348)
Accounts receivable, net	0	0
Other current assets	(2,186)	(19,892)
Property, plant and equipment, net	0	0
Investments in subsidiaries	(3,785,120)	(3,682,115)
Intercompany debt receivable	(36,491)	(113,530)
Goodwill	0	0
Permits and other intangibles, net	0	0
Other long-term assets	3	0
Total assets	(4,799,297)	(4,696,885)
LIABILITIES AND STOCKHOLDERS' EQUITY
Current liabilities	(2,186)	(19,892)
Intercompany payables	(975,503)	(881,348)
Closure, post-closure and remedial liabilities, net	0	0
Long-term obligations, less current portion	0	0
Intercompany debt payable	(36,491)	(113,530)
Other long-term liabilities	3	0
Total liabilities	(1,014,177)	(1,014,770)
Stockholders’ equity	(3,785,120)	(3,682,115)
Total liabilities and stockholders’ equity	$ (4,799,297)	$ (4,696,885)