Fair Value Measurements (Details 1) (Fair Value, Measurements, Recurring, USD $) In Thousands, unless otherwise specified	Jul. 31, 2014
Total
Assets:
Assets measured at fair value	$ 626,119
Liabilities:
Liabilities measured at fair value	390
Level 1
Assets:
Assets measured at fair value	390,006
Liabilities:
Liabilities measured at fair value	0
Level 2
Assets:
Assets measured at fair value	236,113
Liabilities:
Liabilities measured at fair value	390
Level 3
Assets:
Assets measured at fair value	0
Liabilities:
Liabilities measured at fair value	0
Cash equivalents | Total
Assets:
Assets measured at fair value	440,001
Cash equivalents | Level 1
Assets:
Assets measured at fair value	390,006
Cash equivalents | Level 2
Assets:
Assets measured at fair value	49,995
Cash equivalents | Level 3
Assets:
Assets measured at fair value	0
Short-term investments | Total
Assets:
Assets measured at fair value	120,250
Short-term investments | Level 1
Assets:
Assets measured at fair value	0
Short-term investments | Level 2
Assets:
Assets measured at fair value	120,250
Short-term investments | Level 3
Assets:
Assets measured at fair value	0
Prepaid expenses and other | Total
Assets:
Assets measured at fair value	849
Prepaid expenses and other | Level 1
Assets:
Assets measured at fair value	0
Prepaid expenses and other | Level 2
Assets:
Assets measured at fair value	849
Prepaid expenses and other | Level 3
Assets:
Assets measured at fair value	0
Long-term investments | Total
Assets:
Assets measured at fair value	65,019
Long-term investments | Level 1
Assets:
Assets measured at fair value	0
Long-term investments | Level 2
Assets:
Assets measured at fair value	65,019
Long-term investments | Level 3
Assets:
Assets measured at fair value	0
Total assets measured at fair value | Total
Liabilities:
Liabilities measured at fair value	390
Total assets measured at fair value | Level 1
Liabilities:
Liabilities measured at fair value	0
Total assets measured at fair value | Level 2
Liabilities:
Liabilities measured at fair value	390
Total assets measured at fair value | Level 3
Liabilities:
Liabilities measured at fair value	$ 0