Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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The aggregate expense recognized in the current period that allocates the cost of tangible assets, intangible assets, or depleting assets to periods that benefit from use of the assets.

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Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount of the cost of borrowed funds accounted for as interest expense.

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The cash outflow for purchases of and capital improvements on property, plant and equipment (capital expenditures), software, and other intangible assets.

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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).

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Segment Reporting - Summary of Financial Information by Reportable Segment (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]
Inter-company 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
Depreciation and amortization																41,485	40,618	60,339	56,576	58,415
Operating income (loss)	2,708us-gaap_OperatingIncomeLoss	10,064us-gaap_OperatingIncomeLoss	9,338us-gaap_OperatingIncomeLoss	(5,973)us-gaap_OperatingIncomeLoss	(1,298)us-gaap_OperatingIncomeLoss	9,450us-gaap_OperatingIncomeLoss	9,737us-gaap_OperatingIncomeLoss	2,110us-gaap_OperatingIncomeLoss	78us-gaap_OperatingIncomeLoss	4,426us-gaap_OperatingIncomeLoss	5,807us-gaap_OperatingIncomeLoss	(37,679)us-gaap_OperatingIncomeLoss	4,448us-gaap_OperatingIncomeLoss	11,730us-gaap_OperatingIncomeLoss	10,468us-gaap_OperatingIncomeLoss	22,110us-gaap_OperatingIncomeLoss	21,891us-gaap_OperatingIncomeLoss	11,916us-gaap_OperatingIncomeLoss	12,421us-gaap_OperatingIncomeLoss	(11,033)us-gaap_OperatingIncomeLoss
Interest Expense, Net																25,639us-gaap_InterestExpense	25,357us-gaap_InterestExpense	38,175us-gaap_InterestExpense	41,570us-gaap_InterestExpense	45,008us-gaap_InterestExpense
Capital expenditures																55,061		45,959	55,027	58,364
Goodwill	119,170us-gaap_Goodwill			119,139us-gaap_Goodwill				115,928us-gaap_Goodwill				101,706us-gaap_Goodwill				119,170us-gaap_Goodwill		119,139us-gaap_Goodwill	115,928us-gaap_Goodwill	101,706us-gaap_Goodwill
Total Assets	669,795us-gaap_Assets			649,897us-gaap_Assets				663,119us-gaap_Assets				633,743us-gaap_Assets				669,795us-gaap_Assets		649,897us-gaap_Assets	663,119us-gaap_Assets	633,743us-gaap_Assets
Recycling [Member]
Segment Reporting Information [Line Items]
Inter-company revenues																33,741		43,825	42,273	52,195
Depreciation and amortization																2,876		4,262	4,303	4,130
Operating income (loss)																(238)		(2,435)	(697)	5,088
Interest Expense, Net																			5,553	6,795
Capital expenditures																3,016		1,111	935	5,494
Goodwill	12,315			12,315				12,190				12,190				12,315		12,315	12,190	12,190
Total Assets	52,016			49,652				50,921				55,434				52,016		49,652	50,921	55,434
Other [Member]
Segment Reporting Information [Line Items]
Inter-company revenues																69,333		89,567	77,426	75,598
Depreciation and amortization																1,639		2,423	2,309	2,938
Operating income (loss)																74		2,158	(1,649)	(2,196)
Interest Expense, Net																25,713		38,023	10,133	6,454
Capital expenditures																2,807		4,507	3,325	5,669
Goodwill	1,729			1,729												1,729		1,729
Total Assets	73,731			68,706				65,033				77,990				73,731		68,706	65,033	77,990
Intersubsegment Eliminations [Member] \| Recycling [Member]
Segment Reporting Information [Line Items]
Inter-company revenues																(175)		(139)	116	57
Intersubsegment Eliminations [Member] \| Other [Member]
Segment Reporting Information [Line Items]
Inter-company revenues																1,763		2,019	3,933	4,466
Eastern Region [Member]
Segment Reporting Information [Line Items]
Inter-company revenues																108,423		147,330	129,889	127,930
Depreciation and amortization																17,195		24,961	23,518	25,179
Operating income (loss)																3,434		(1,105)	(5,291)	(43,640)
Interest Expense, Net																(315)		(272)	27,054	31,637
Capital expenditures																27,354		19,870	20,383	19,734
Goodwill	17,429			17,429				16,858				58				17,429		17,429	16,858	58
Total Assets	211,020			200,235				198,710				166,938				211,020		200,235	198,710	166,938
Eastern Region [Member] \| Intersubsegment Eliminations [Member]
Segment Reporting Information [Line Items]
Inter-company revenues																31,840		38,946	30,933	33,559
Western Region [Member]
Segment Reporting Information [Line Items]
Inter-company revenues																156,877		216,911	205,747	212,227
Depreciation and amortization																19,775		28,693	26,446	26,168
Operating income (loss)																18,840		13,298	20,058	29,715
Interest Expense, Net																(6)		112	(1,311)	80
Capital expenditures																21,884		20,471	30,384	27,467
Goodwill	87,697			87,666				86,880				89,458				87,697		87,666	86,880	89,458
Total Assets	333,028			331,304				348,455				333,381				333,028		331,304	348,455	333,381
Western Region [Member] \| Intersubsegment Eliminations [Member]
Segment Reporting Information [Line Items]
Inter-company revenues																50,235		70,809	65,390	67,776
Elimination [Member]
Segment Reporting Information [Line Items]
Inter-company revenues
Depreciation and amortization
Operating income (loss)
Interest Expense, Net																			(32,868)	(39,863)
Goodwill
Total Assets	9,888			36,006				59,759								9,888		36,006	59,759
Elimination [Member] \| Intersubsegment Eliminations [Member]
Segment Reporting Information [Line Items]
Inter-company revenues																$ (83,663)		$ (111,635)	$ (100,372)	$ (105,858)