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Segment Reporting - Summary of Revenue Attributable to Services Provided by Company (Detail) (USD $) In Thousands, unless otherwise specified	2 Months Ended	3 Months Ended														8 Months Ended		12 Months Ended
	Dec. 31, 2014	Oct. 31, 2014	Jul. 31, 2014	Apr. 30, 2014	Jan. 31, 2014	Oct. 31, 2013	Jul. 31, 2013	Apr. 30, 2013	Jan. 31, 2013	Oct. 31, 2012	Jul. 31, 2012	Apr. 30, 2012	Jan. 31, 2012	Oct. 31, 2011	Jul. 31, 2011	Dec. 31, 2014	Dec. 31, 2013	Apr. 30, 2014	Apr. 30, 2013	Apr. 30, 2012
Segment Reporting Information [Line Items]
Revenues	$ 85,646us-gaap_Revenues	$ 141,341us-gaap_Revenues	$ 141,387us-gaap_Revenues	$ 118,927us-gaap_Revenues	$ 117,852us-gaap_Revenues	$ 132,296us-gaap_Revenues	$ 128,558us-gaap_Revenues	$ 108,694us-gaap_Revenues	$ 112,167us-gaap_Revenues	$ 116,836us-gaap_Revenues	$ 117,638us-gaap_Revenues	$ 106,375us-gaap_Revenues	$ 111,520us-gaap_Revenues	$ 125,989us-gaap_Revenues	$ 124,066us-gaap_Revenues	$ 368,374us-gaap_Revenues	$ 340,069us-gaap_Revenues	$ 497,633us-gaap_Revenues	$ 455,335us-gaap_Revenues	$ 467,950us-gaap_Revenues
Revenues percentage																100.00%us-gaap_ConcentrationRiskPercentage1		100.00%us-gaap_ConcentrationRiskPercentage1	100.00%us-gaap_ConcentrationRiskPercentage1	100.00%us-gaap_ConcentrationRiskPercentage1
Solid Waste Operations [Member]
Segment Reporting Information [Line Items]
Revenues																271,805us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cwst_SolidWasteOperationsMember		372,583us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cwst_SolidWasteOperationsMember	342,277us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cwst_SolidWasteOperationsMember	346,582us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cwst_SolidWasteOperationsMember
Solid Waste Operations [Member] | Sales Revenue, Product Line [Member] | Product Concentration Risk [Member]
Segment Reporting Information [Line Items]
Revenues percentage																73.80%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueProductLineMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_ProductConcentrationRiskMember / us-gaap_StatementBusinessSegmentsAxis = cwst_SolidWasteOperationsMember		74.90%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueProductLineMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_ProductConcentrationRiskMember / us-gaap_StatementBusinessSegmentsAxis = cwst_SolidWasteOperationsMember	75.10%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueProductLineMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_ProductConcentrationRiskMember / us-gaap_StatementBusinessSegmentsAxis = cwst_SolidWasteOperationsMember	74.10%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueProductLineMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_ProductConcentrationRiskMember / us-gaap_StatementBusinessSegmentsAxis = cwst_SolidWasteOperationsMember
Solid Waste Operations [Member] | Collection [Member]
Segment Reporting Information [Line Items]
Revenues																157,809us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cwst_SolidWasteOperationsMember / us-gaap_SubsegmentsAxis = cwst_CollectionMember		225,441us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cwst_SolidWasteOperationsMember / us-gaap_SubsegmentsAxis = cwst_CollectionMember	208,973us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cwst_SolidWasteOperationsMember / us-gaap_SubsegmentsAxis = cwst_CollectionMember	205,296us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cwst_SolidWasteOperationsMember / us-gaap_SubsegmentsAxis = cwst_CollectionMember
Solid Waste Operations [Member] | Collection [Member] | Sales Revenue, Product Line [Member] | Product Concentration Risk [Member]
Segment Reporting Information [Line Items]
Revenues percentage																42.80%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueProductLineMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_ProductConcentrationRiskMember / us-gaap_StatementBusinessSegmentsAxis = cwst_SolidWasteOperationsMember / us-gaap_SubsegmentsAxis = cwst_CollectionMember		45.30%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueProductLineMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_ProductConcentrationRiskMember / us-gaap_StatementBusinessSegmentsAxis = cwst_SolidWasteOperationsMember / us-gaap_SubsegmentsAxis = cwst_CollectionMember	45.90%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueProductLineMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_ProductConcentrationRiskMember / us-gaap_StatementBusinessSegmentsAxis = cwst_SolidWasteOperationsMember / us-gaap_SubsegmentsAxis = cwst_CollectionMember	43.90%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueProductLineMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_ProductConcentrationRiskMember / us-gaap_StatementBusinessSegmentsAxis = cwst_SolidWasteOperationsMember / us-gaap_SubsegmentsAxis = cwst_CollectionMember
Solid Waste Operations [Member] | Disposal [Member]
Segment Reporting Information [Line Items]
Revenues																102,304us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cwst_SolidWasteOperationsMember / us-gaap_SubsegmentsAxis = cwst_DisposalMember		128,778us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cwst_SolidWasteOperationsMember / us-gaap_SubsegmentsAxis = cwst_DisposalMember	115,049us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cwst_SolidWasteOperationsMember / us-gaap_SubsegmentsAxis = cwst_DisposalMember	123,620us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cwst_SolidWasteOperationsMember / us-gaap_SubsegmentsAxis = cwst_DisposalMember
Solid Waste Operations [Member] | Disposal [Member] | Sales Revenue, Product Line [Member] | Product Concentration Risk [Member]
Segment Reporting Information [Line Items]
Revenues percentage																27.80%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueProductLineMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_ProductConcentrationRiskMember / us-gaap_StatementBusinessSegmentsAxis = cwst_SolidWasteOperationsMember / us-gaap_SubsegmentsAxis = cwst_DisposalMember		25.90%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueProductLineMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_ProductConcentrationRiskMember / us-gaap_StatementBusinessSegmentsAxis = cwst_SolidWasteOperationsMember / us-gaap_SubsegmentsAxis = cwst_DisposalMember	25.30%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueProductLineMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_ProductConcentrationRiskMember / us-gaap_StatementBusinessSegmentsAxis = cwst_SolidWasteOperationsMember / us-gaap_SubsegmentsAxis = cwst_DisposalMember	26.40%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueProductLineMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_ProductConcentrationRiskMember / us-gaap_StatementBusinessSegmentsAxis = cwst_SolidWasteOperationsMember / us-gaap_SubsegmentsAxis = cwst_DisposalMember
Solid Waste Operations [Member] | Power Generation [Member]
Segment Reporting Information [Line Items]
Revenues																5,049us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cwst_SolidWasteOperationsMember / us-gaap_SubsegmentsAxis = cwst_PowerGenerationMember		9,512us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cwst_SolidWasteOperationsMember / us-gaap_SubsegmentsAxis = cwst_PowerGenerationMember	11,354us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cwst_SolidWasteOperationsMember / us-gaap_SubsegmentsAxis = cwst_PowerGenerationMember	11,894us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cwst_SolidWasteOperationsMember / us-gaap_SubsegmentsAxis = cwst_PowerGenerationMember
Solid Waste Operations [Member] | Power Generation [Member] | Sales Revenue, Product Line [Member] | Product Concentration Risk [Member]
Segment Reporting Information [Line Items]
Revenues percentage																1.40%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueProductLineMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_ProductConcentrationRiskMember / us-gaap_StatementBusinessSegmentsAxis = cwst_SolidWasteOperationsMember / us-gaap_SubsegmentsAxis = cwst_PowerGenerationMember		1.90%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueProductLineMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_ProductConcentrationRiskMember / us-gaap_StatementBusinessSegmentsAxis = cwst_SolidWasteOperationsMember / us-gaap_SubsegmentsAxis = cwst_PowerGenerationMember	2.40%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueProductLineMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_ProductConcentrationRiskMember / us-gaap_StatementBusinessSegmentsAxis = cwst_SolidWasteOperationsMember / us-gaap_SubsegmentsAxis = cwst_PowerGenerationMember	2.60%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueProductLineMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_ProductConcentrationRiskMember / us-gaap_StatementBusinessSegmentsAxis = cwst_SolidWasteOperationsMember / us-gaap_SubsegmentsAxis = cwst_PowerGenerationMember
Solid Waste Operations [Member] | Processing [Member]
Segment Reporting Information [Line Items]
Revenues																6,643us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cwst_SolidWasteOperationsMember / us-gaap_SubsegmentsAxis = cwst_ProcessingMember		8,852us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cwst_SolidWasteOperationsMember / us-gaap_SubsegmentsAxis = cwst_ProcessingMember	6,901us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cwst_SolidWasteOperationsMember / us-gaap_SubsegmentsAxis = cwst_ProcessingMember	5,772us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cwst_SolidWasteOperationsMember / us-gaap_SubsegmentsAxis = cwst_ProcessingMember
Solid Waste Operations [Member] | Processing [Member] | Sales Revenue, Product Line [Member] | Product Concentration Risk [Member]
Segment Reporting Information [Line Items]
Revenues percentage																1.80%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueProductLineMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_ProductConcentrationRiskMember / us-gaap_StatementBusinessSegmentsAxis = cwst_SolidWasteOperationsMember / us-gaap_SubsegmentsAxis = cwst_ProcessingMember		1.80%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueProductLineMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_ProductConcentrationRiskMember / us-gaap_StatementBusinessSegmentsAxis = cwst_SolidWasteOperationsMember / us-gaap_SubsegmentsAxis = cwst_ProcessingMember	1.50%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueProductLineMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_ProductConcentrationRiskMember / us-gaap_StatementBusinessSegmentsAxis = cwst_SolidWasteOperationsMember / us-gaap_SubsegmentsAxis = cwst_ProcessingMember	1.20%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueProductLineMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_ProductConcentrationRiskMember / us-gaap_StatementBusinessSegmentsAxis = cwst_SolidWasteOperationsMember / us-gaap_SubsegmentsAxis = cwst_ProcessingMember
Organics [Member]
Segment Reporting Information [Line Items]
Revenues																27,012us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cwst_OrganicsMember		37,829us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cwst_OrganicsMember	35,330us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cwst_OrganicsMember	30,871us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cwst_OrganicsMember
Organics [Member] | Sales Revenue, Product Line [Member] | Product Concentration Risk [Member]
Segment Reporting Information [Line Items]
Revenues percentage																7.30%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueProductLineMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_ProductConcentrationRiskMember / us-gaap_StatementBusinessSegmentsAxis = cwst_OrganicsMember		7.60%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueProductLineMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_ProductConcentrationRiskMember / us-gaap_StatementBusinessSegmentsAxis = cwst_OrganicsMember	7.80%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueProductLineMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_ProductConcentrationRiskMember / us-gaap_StatementBusinessSegmentsAxis = cwst_OrganicsMember	6.60%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueProductLineMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_ProductConcentrationRiskMember / us-gaap_StatementBusinessSegmentsAxis = cwst_OrganicsMember
Customer Solutions [Member]
Segment Reporting Information [Line Items]
Revenues																35,816us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cwst_CustomerSolutionsMember		43,396us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cwst_CustomerSolutionsMember	35,455us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cwst_CustomerSolutionsMember	38,302us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cwst_CustomerSolutionsMember
Customer Solutions [Member] | Sales Revenue, Product Line [Member] | Product Concentration Risk [Member]
Segment Reporting Information [Line Items]
Revenues percentage																9.70%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueProductLineMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_ProductConcentrationRiskMember / us-gaap_StatementBusinessSegmentsAxis = cwst_CustomerSolutionsMember		8.70%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueProductLineMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_ProductConcentrationRiskMember / us-gaap_StatementBusinessSegmentsAxis = cwst_CustomerSolutionsMember	7.80%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueProductLineMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_ProductConcentrationRiskMember / us-gaap_StatementBusinessSegmentsAxis = cwst_CustomerSolutionsMember	8.20%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueProductLineMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_ProductConcentrationRiskMember / us-gaap_StatementBusinessSegmentsAxis = cwst_CustomerSolutionsMember
Recycling [Member]
Segment Reporting Information [Line Items]
Revenues																$ 33,741us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cwst_RecyclingMember		$ 43,825us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cwst_RecyclingMember	$ 42,273us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cwst_RecyclingMember	$ 52,195us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cwst_RecyclingMember
Recycling [Member] | Sales Revenue, Product Line [Member] | Product Concentration Risk [Member]
Segment Reporting Information [Line Items]
Revenues percentage																9.20%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueProductLineMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_ProductConcentrationRiskMember / us-gaap_StatementBusinessSegmentsAxis = cwst_RecyclingMember		8.80%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueProductLineMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_ProductConcentrationRiskMember / us-gaap_StatementBusinessSegmentsAxis = cwst_RecyclingMember	9.30%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueProductLineMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_ProductConcentrationRiskMember / us-gaap_StatementBusinessSegmentsAxis = cwst_RecyclingMember	11.10%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueProductLineMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_ProductConcentrationRiskMember / us-gaap_StatementBusinessSegmentsAxis = cwst_RecyclingMember

X

- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 21

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13537-108611



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 275

-SubTopic 10

-Section 50

-Paragraph 20

-URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6404-108592



Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 20

-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13531-108611



Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 275

-SubTopic 10

-Section 50

-Paragraph 18

-URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6351-108592

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X

- Definition

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.1)

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Article 5

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