Commitments and Contingencies - Schedule of Environmental Liability Associated with Postdam (Detail) (USD $) In Thousands, unless otherwise specified	8 Months Ended	12 Months Ended
Dec. 31, 2014	Apr. 30, 2014	Apr. 30, 2013
Site Contingency [Line Items]
Ending balance	$ 5,142
Potsdam Environmental Remediation Liability [Member]
Site Contingency [Line Items]
Beginning balance	5,320	5,297	5,210
Revisions in estimates		(118)
Payments	(270)	(28)	(51)
Ending balance	5,142	5,320	5,297
Potsdam Environmental Remediation Liability [Member] \| Obligations Incurred [Member]
Site Contingency [Line Items]
Obligations incurred / Accretion expense		31
Potsdam Environmental Remediation Liability [Member] \| Accretion Expense [Member]
Site Contingency [Line Items]
Obligations incurred / Accretion expense	$ 92	$ 138	$ 138

Total costs accrued as of the balance sheet date for environmental loss contingencies.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 410

-SubTopic 30

-Section 50

-Paragraph 7

-URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13207-110859

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 1

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

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-Name Accounting Standards Codification

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The Increase or Decrease in the accrual for environmental loss in the period from revisions in estimates to existing obligations. The amount does not relate to changes in the environmental accrual related to business acquisitions or divestitures, or to currency movements.

+ References

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

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-Name Accounting Standards Codification

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-SubTopic 20

-Section S99

-Paragraph 1

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The aggregate amount disbursed during the reporting period to settle environmental loss contingencies.

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