Fair Value Measurements (Fair Value Of Assets On Recurring Basis) (Details) (USD $) In Thousands, unless otherwise specified	Jan. 31, 2013	Apr. 30, 2012
Fair Value Measurements Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	$ 47,401	$ 40,231
Fair Value Measurements Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	0	0
Fair Value Measurements Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	0	0
Money Market Funds [Member] | Fair Value Measurements Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	45,940	38,874
Mutual Funds [Member] | Fair Value Measurements Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	$ 1,461	$ 1,357