Fair Value Measurements (Details 1) (Fair Value, Measurements, Recurring [Member], USD $) In Thousands, unless otherwise specified	Apr. 30, 2013
Total [Member]
Assets:
Short-term investments	$ 99,973
Prepaid expenses and other	52
Other long-term assets	220
Total assets measured at fair value	100,245
Liabilities:
Accrued liabilities	67
Total liabilities measured at fair value	67
Level 1 [Member]
Assets:
Short-term investments	99,973
Prepaid expenses and other	0
Other long-term assets	0
Total assets measured at fair value	99,973
Liabilities:
Accrued liabilities	0
Total liabilities measured at fair value	0
Level 2 [Member]
Assets:
Short-term investments	0
Prepaid expenses and other	52
Other long-term assets	0
Total assets measured at fair value	52
Liabilities:
Accrued liabilities	67
Total liabilities measured at fair value	67
Level 3 [Member]
Assets:
Short-term investments	0
Prepaid expenses and other	0
Other long-term assets	220
Total assets measured at fair value	220
Liabilities:
Accrued liabilities	0
Total liabilities measured at fair value	$ 0