Investments - Additional Information (Detail) - USD ($)	12 Months Ended
Apr. 30, 2015	Apr. 30, 2014	Apr. 30, 2013
Schedule of Held-to-maturity Securities [Line Items]
Carrying value of investment	$ 30,740,000	$ 23,771,000
Trading investments	13,156,000	8,975,000
Net unrealized holding gains	$ 405,000	$ 160,000	$ 815,000

Sum of the carrying amounts as of the balance sheet date of all investments.

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

-Publisher FASB

-Name Accounting Standards Codification

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The total amount of investments that are intended to be held for an extended period of time (longer than one operating cycle).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

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Amount of unrealized holding gain (loss) recognized in the income statement for investments in debt and equity securities and other forms of securities that provide ownership interests classified as trading.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Trading Securities

-URI http://asc.fasb.org/extlink&oid=6526789

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

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

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