GUARANTOR AND NON-GUARANTOR SUBSIDIARIES FINANCIAL INFORMATION (Condensed Consolidating Balance Sheets) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
ASSETS
Cash and cash equivalents	$ 167,371	$ 226,507	$ 186,352	$ 319,399
Short-term marketable securities	57,477	52,856
Intercompany receivables	0	0
Accounts receivable, net	613,507	606,952
Other current assets	309,767	315,843
Property, plant and equipment, net	1,588,613	1,561,978
Investments in subsidiaries	0	0
Intercompany debt receivable	0	0
Operating lease right-of-use asset	170,550
Goodwill	517,910	514,189
Permits and other intangibles, net	438,958	441,875
Other long-term assets	17,901	18,121
Total assets	3,882,054	3,738,321
LIABILITIES AND STOCKHOLDERS' EQUITY
Current liabilities	597,510	602,278
Intercompany payables	0	0
Closure, post-closure and remedial liabilities, net	165,468	167,914
Long-term obligations, less current portion	1,564,005	1,565,021
Operating lease liabilities, less current portion	128,689
Intercompany debt payable	0	0
Other long-term liabilities	254,417	233,352
Total liabilities	2,710,089	2,568,565
Stockholders’ equity	1,171,965	1,169,756	1,145,526	1,188,202
Total liabilities and stockholders’ equity	3,882,054	3,738,321
Reportable Legal Entities | Clean Harbors, Inc.
ASSETS
Cash and cash equivalents	27,431	27,308	51,781	51,638
Short-term marketable securities	121	67
Intercompany receivables	268,195	262,475
Accounts receivable, net	0	0
Other current assets	0	0
Property, plant and equipment, net	0	0
Investments in subsidiaries	3,176,613	3,162,704
Intercompany debt receivable	0	0
Operating lease right-of-use asset	0
Goodwill	0	0
Permits and other intangibles, net	0	0
Other long-term assets	1,437	1,551
Total assets	3,473,797	3,454,105
LIABILITIES AND STOCKHOLDERS' EQUITY
Current liabilities	35,686	20,170
Intercompany payables	702,141	699,158
Closure, post-closure and remedial liabilities, net	0	0
Long-term obligations, less current portion	1,564,005	1,565,021
Operating lease liabilities, less current portion	0
Intercompany debt payable	0	0
Other long-term liabilities	0	0
Total liabilities	2,301,832	2,284,349
Stockholders’ equity	1,171,965	1,169,756
Total liabilities and stockholders’ equity	3,473,797	3,454,105
Reportable Legal Entities | Guarantor Subsidiaries
ASSETS
Cash and cash equivalents	75,099	101,302	99,662	207,777
Short-term marketable securities	0	0
Intercompany receivables	701,583	721,521
Accounts receivable, net	526,047	520,785
Other current assets	281,802	289,869
Property, plant and equipment, net	1,261,206	1,233,578
Investments in subsidiaries	566,296	571,304
Intercompany debt receivable	14,900	14,669
Operating lease right-of-use asset	137,591
Goodwill	459,139	456,307
Permits and other intangibles, net	390,838	393,045
Other long-term assets	13,530	13,545
Total assets	4,428,031	4,315,925
LIABILITIES AND STOCKHOLDERS' EQUITY
Current liabilities	431,891	457,164
Intercompany payables	325,025	321,846
Closure, post-closure and remedial liabilities, net	147,944	151,480
Long-term obligations, less current portion	0	0
Operating lease liabilities, less current portion	104,374
Intercompany debt payable	21,000	21,000
Other long-term liabilities	233,979	212,924
Total liabilities	1,264,213	1,164,414
Stockholders’ equity	3,163,818	3,151,511
Total liabilities and stockholders’ equity	4,428,031	4,315,925
Reportable Legal Entities | Non-Guarantor Subsidiaries
ASSETS
Cash and cash equivalents	64,841	97,897	34,909	59,984
Short-term marketable securities	57,356	52,789
Intercompany receivables	58,138	60,693
Accounts receivable, net	87,460	86,167
Other current assets	44,525	49,631
Property, plant and equipment, net	327,407	328,400
Investments in subsidiaries	0	0
Intercompany debt receivable	21,000	21,000
Operating lease right-of-use asset	32,959
Goodwill	58,771	57,882
Permits and other intangibles, net	48,120	48,830
Other long-term assets	2,903	3,025
Total assets	803,480	806,314
LIABILITIES AND STOCKHOLDERS' EQUITY
Current liabilities	146,493	148,601
Intercompany payables	750	23,685
Closure, post-closure and remedial liabilities, net	17,524	16,434
Long-term obligations, less current portion	0	0
Operating lease liabilities, less current portion	24,315
Intercompany debt payable	14,900	14,669
Other long-term liabilities	20,407	20,428
Total liabilities	224,389	223,817
Stockholders’ equity	579,091	582,497
Total liabilities and stockholders’ equity	803,480	806,314
Consolidating Adjustments
ASSETS
Cash and cash equivalents	0	0	$ 0	$ 0
Short-term marketable securities	0	0
Intercompany receivables	(1,027,916)	(1,044,689)
Accounts receivable, net	0	0
Other current assets	(16,560)	(23,657)
Property, plant and equipment, net	0	0
Investments in subsidiaries	(3,742,909)	(3,734,008)
Intercompany debt receivable	(35,900)	(35,669)
Operating lease right-of-use asset	0
Goodwill	0	0
Permits and other intangibles, net	0	0
Other long-term assets	31	0
Total assets	(4,823,254)	(4,838,023)
LIABILITIES AND STOCKHOLDERS' EQUITY
Current liabilities	(16,560)	(23,657)
Intercompany payables	(1,027,916)	(1,044,689)
Closure, post-closure and remedial liabilities, net	0	0
Long-term obligations, less current portion	0	0
Operating lease liabilities, less current portion	0
Intercompany debt payable	(35,900)	(35,669)
Other long-term liabilities	31	0
Total liabilities	(1,080,345)	(1,104,015)
Stockholders’ equity	(3,742,909)	(3,734,008)
Total liabilities and stockholders’ equity	$ (4,823,254)	$ (4,838,023)