Organization and Summary of Significant Accounting Policies - Levels of fair value measurements of investments (Details) (USD $) In Thousands, unless otherwise specified	Jul. 31, 2014	Apr. 30, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	$ 6,466	$ 5,482
Securities available-for-sale	9,095	9,226
Investments, fair value disclosure	15,561	14,708
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	6,466	5,482
Securities available-for-sale	9,095	9,226
Investments, fair value disclosure	15,561	14,708
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents
Securities available-for-sale
Investments, fair value disclosure
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents
Securities available-for-sale
Investments, fair value disclosure