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Stockholders' (Deficit) Equity - Additional Information (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Apr. 30, 2014	Apr. 30, 2013	Apr. 30, 2012
Limited Partners' Capital Account [Line Items]
Aggregate intrinsic value of stock options exercised	$ 23	$ 23	$ 23
Weighted average fair value stock options granted	$ 5.65	$ 3.03	$ 4.14
Total fair value of other stock awards vested	1,458	2,475	2,056
Tax benefits from additional paid-in-capital adjustments	0	96	254
Stock Options [Member]
Limited Partners' Capital Account [Line Items]
Stock-based compensation expense	464	528	258
Unrecognized stock-based compensation expense	754
Unrecognized stock-based compensation expense, weighted average period	1 year 9 months 18 days
Restricted Stock, Restricted Stock Units and Performance Stock Units [Member]
Limited Partners' Capital Account [Line Items]
Stock-based compensation expense	1,861	1,609	1,485
Income taxes associated with stock-based compensation expense	0	0	0
Restricted Stock and Restricted Stock Unit [Member]
Limited Partners' Capital Account [Line Items]
Unrecognized stock-based compensation expense	2,044
Unrecognized stock-based compensation expense, weighted average period	1 year 7 months 6 days
Performance Stock Units [Member]
Limited Partners' Capital Account [Line Items]
Unrecognized stock-based compensation expense	2,390
Unrecognized stock-based compensation expense, weighted average period	1 year
Employee Stock Purchase Plan [Member]
Limited Partners' Capital Account [Line Items]
Stock-based compensation expense	79	99	113
Altela, Inc. [Member]
Limited Partners' Capital Account [Line Items]
Membership interest	51.00%
Casella-Altela Regional Environmental Services, LLC [Member] | Altela, Inc. [Member]
Limited Partners' Capital Account [Line Items]
Membership interest	49.00%
Maximum [Member] | 2006 Stock Incentive Plan [Member]
Limited Partners' Capital Account [Line Items]
Options vesting period	4 years
Options granted period	10 years
Minimum [Member] | 2006 Stock Incentive Plan [Member]
Limited Partners' Capital Account [Line Items]
Options vesting period	1 year
Class A Common Stock [Member]
Limited Partners' Capital Account [Line Items]
Issuances of Class A common stock		11,500
Share price		$ 4.00
Net proceeds from the registered public offering		$ 42,184
Class A Common Stock [Member] | 2006 Stock Incentive Plan [Member]
Limited Partners' Capital Account [Line Items]
Common stock, issued shares	2,475
Number of shares available for future grant	1,414
Class A Common Stock [Member] | Maximum [Member] | 1997 Non-Employee Director Stock Option Plan [Member]
Limited Partners' Capital Account [Line Items]
Common stock, issued shares	200
Preferred Stock [Member]
Limited Partners' Capital Account [Line Items]
Shares issued	0	0
Preferred Stock [Member] | Maximum [Member]
Limited Partners' Capital Account [Line Items]
Preferred stock authorized to issue	944

X

- Definition

The number of shares that can be issued under the plan as a result of the grant of non-statutory options.

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Amount of increase in additional paid in capital (APIC) resulting from a tax benefit associated with share-based compensation plan other than an employee stock ownership plan (ESOP). Includes, but is not limited to, excess tax benefit.

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Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Aggregate number of common shares reserved for future issuance.

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Unrecognized cost of unvested share-based awards, other than options, awarded to employees as compensation.

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Disclosure of the aggregate tax benefit realized from the exercise of stock options and the conversion of similar instruments during the annual period.

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The parent entity's interest in net assets of the subsidiary, expressed as a percentage.

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The maximum number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) permitted to be issued by an entity's charter and bylaws.

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Total number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) issued to shareholders (includes related preferred shares that were issued, repurchased, and remain in the treasury). May be all or portion of the number of preferred shares authorized. Excludes preferred shares that are classified as debt.

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The cash inflow from the issuance of common stock, preferred stock, treasury stock, stock options, and other types of equity.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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Price of a single share of a number of saleable stocks of a company.

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Number of new stock issued during the period.

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