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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 |  |

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