Subsidiary Guarantors - Schedule of Condensed Consolidating Statement of Cash Flows (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Condensed Financial Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	$ (5,695)	$ 1,361
Cash Flows from Investing Activities:
Acquisitions, net of cash acquired		214us-gaap_ProceedsFromPreviousAcquisition
Additions to property, plant and equipment	(4,444)	(7,477)
Payments on landfill operating lease contracts	(478)cwst_PaymentsForLandfillOperatingLease	(563)cwst_PaymentsForLandfillOperatingLease
Payments related to investments		(84)us-gaap_PaymentsToAcquireInvestments
Proceeds from sale of property and equipment	89	216
Net cash provided by (used in) investing activities	(283)	(7,773)
Proceeds from divestiture transactions	4,550
Cash Flows from Financing Activities:
Proceeds from long-term borrowings	197,591	47,860
Principal payments on long-term debt	(186,500)	(41,250)
Payments of financing costs	(6,852)us-gaap_PaymentsOfFinancingCosts	(17)us-gaap_PaymentsOfFinancingCosts
Net cash provided by (used in) financing activities	6,830	6,593
Change in restricted cash	4,086
Distributions to noncontrolling interest holder	(1,495)us-gaap_PaymentsToMinorityShareholders
Net cash provided by (used in) discontinued operations		86
Net increase (decrease) in cash and cash equivalents	852	267
Cash and cash equivalents, beginning of period	2,205	2,695
Cash and cash equivalents, end of period	3,057	2,962
Acquisition [Member]
Cash Flows from Investing Activities:
Additions to property, plant and equipment	(4,444)	(79)
Parent [Member]
Condensed Financial Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	(10,886)	(5,327)
Cash Flows from Investing Activities:
Additions to property, plant and equipment		(256)
Net cash provided by (used in) investing activities	(516)	(256)
Cash Flows from Financing Activities:
Proceeds from long-term borrowings	197,573	47,860
Principal payments on long-term debt	(186,267)	(41,120)
Payments of financing costs	(6,852)	(17)
Intercompany borrowings	3,707	(718)
Net cash provided by (used in) financing activities	12,247	6,005
Change in restricted cash	4,086
Net increase (decrease) in cash and cash equivalents	845	422
Cash and cash equivalents, beginning of period	1,596	2,312
Cash and cash equivalents, end of period	2,441	2,734
Parent [Member] \| Acquisition [Member]
Cash Flows from Investing Activities:
Additions to property, plant and equipment	(516)
Guarantors [Member]
Condensed Financial Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	5,604	6,799
Cash Flows from Investing Activities:
Acquisitions, net of cash acquired		214
Additions to property, plant and equipment		(7,221)
Payments on landfill operating lease contracts	(478)	(563)
Payments related to investments	1,555	(84)
Proceeds from sale of property and equipment	89	216
Net cash provided by (used in) investing activities	(1,712)	(7,517)
Proceeds from divestiture transactions	1,050
Cash Flows from Financing Activities:
Proceeds from long-term borrowings	18
Principal payments on long-term debt	(233)	(130)
Intercompany borrowings	(3,707)	718
Net cash provided by (used in) financing activities	(3,922)	588
Net cash provided by (used in) discontinued operations		86
Net increase (decrease) in cash and cash equivalents	(30)	(44)
Cash and cash equivalents, beginning of period	253	243
Cash and cash equivalents, end of period	223	199
Guarantors [Member] \| Acquisition [Member]
Cash Flows from Investing Activities:
Additions to property, plant and equipment	(3,928)	(79)
Non-Guarantors [Member]
Condensed Financial Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	(413)	(111)
Cash Flows from Investing Activities:
Payments related to investments	(1,555)
Net cash provided by (used in) investing activities	1,945
Proceeds from divestiture transactions	3,500
Cash Flows from Financing Activities:
Net cash provided by (used in) financing activities	(1,495)
Distributions to noncontrolling interest holder	(1,495)
Net increase (decrease) in cash and cash equivalents	37	(111)
Cash and cash equivalents, beginning of period	356	140
Cash and cash equivalents, end of period	$ 393	$ 29

The intercompany cash outflow/inflow associated with intercompany transactions.

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- Definition

The cash outflow associated with landfill operating agreements consisting of up-front or one-time payments, future minimum rental payments, including success/expansion fees, other direct costs and capping, closure and post closure costs.

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Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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Amount of increase (decrease) in cash and cash equivalents. Cash and cash equivalents are the amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Includes effect from exchange rate changes.

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Increase (decrease) in cash associated with the entity's discontinued operations.

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Amount of cash inflow (outflow) of financing activities, excluding discontinued operations. Financing activity cash flows include obtaining resources from owners and providing them with a return on, and a return of, their investment; borrowing money and repaying amounts borrowed, or settling the obligation; and obtaining and paying for other resources obtained from creditors on long-term credit.

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- Definition

Amount of cash inflow (outflow) of investing activities, excluding discontinued operations. Investing activity cash flows include making and collecting loans and acquiring and disposing of debt or equity instruments and property, plant, and equipment and other productive assets.

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Amount of cash inflow (outflow) from operating activities, excluding discontinued operations. Operating activity cash flows include transactions, adjustments, and changes in value not defined as investing or financing activities.

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- Definition

The cash outflow for loan and debt issuance costs.

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-Glossary Financing Activities

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- Definition

The cash outflow associated with the purchase of all investments (debt, security, other) during the period.

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- Definition

The cash outflow associated with the acquisition of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale; includes cash outflows to pay for construction of self-constructed assets.

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Amount of cash outflow to a noncontrolling interest. Includes, but not limited to, reduction of noncontrolling interest ownership. Excludes dividends paid to the noncontrolling interest.

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The cash inflow from a debt initially having maturity due after one year or beyond the operating cycle, if longer.

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Cash inflow representing an adjustment to the purchase price of a previous acquisition.

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No definition available.

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The net cash inflow or outflow from cash and cash items that are not available for withdrawal or usage.

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The cash inflow from the sale of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale.

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Aggregate cash proceeds received from a combination of transactions in which noncurrent assets are sold, which may include the sale of a business, an investment in an affiliate (including an equity method investee), property, plant and equipment and intangible assets. Excludes sales of trading, available-for-sale, and held-to-maturity securities.

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The cash outflow associated with security instruments that either represent a creditor or an ownership relationship with the holder of the investment security with a maturity of beyond one year or normal operating cycle, if longer. Includes repayments of (a) debt, (b) capital lease obligations, (c) mandatory redeemable capital securities, and (d) any combination of (a), (b), or (c).

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