Related Party Transactions - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Jan. 31, 2013	Apr. 30, 2012
Related Party Transaction [Line Items]
Payables and accruals, due	$ 2.0	$ 2.0
Receivables, due	1.0	0.9
Nigerian Company \| Atlantic Aviation
Related Party Transaction [Line Items]
Related party transaction, loan receivable	$ 0.9

Amounts due within 1 year (or 1 business cycle) from other related parties which are not otherwise stated in the taxonomy.

+ References+ Details

For an unclassified balance sheet, amounts due from related parties including affiliates, employees, joint ventures, officers and stockholders, immediate families thereof, and pension funds.

+ References

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

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

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Reference 7: http://www.xbrl.org/2003/role/presentationRef

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 8: http://www.xbrl.org/2003/role/presentationRef

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+ Details

- Definition

Carrying amount as of the balance sheet date of obligations due all related parties.

+ References

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

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+ Details