Cash Equivalents, Short-Term Investments, Restricted Cash and Fair Value Measurements (Schedule of the Fair Value of Assets and Liabilities by Level) (Details) (USD $) | Apr. 30, 2014 | Jul. 31, 2013 |
In Thousands, unless otherwise specified |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Short-term investments | $170,035 | $139,508 |
Level 1 [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Short-term investments | 122,555 | 99,738 |
Total financial assets | 131,865 | 114,278 |
Level 2 [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Short-term investments | 47,480 | 39,770 |
Total financial assets | 47,480 | 39,770 |
Level 3 [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Short-term investments | 0 | 0 |
Total financial assets | 0 | 0 |
Total [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Short-term investments | 170,035 | 139,508 |
Total financial assets | 179,345 | 154,048 |
US Treasury Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Short-term investments | 122,555 | 99,738 |
Restricted cash | 3,412 | 3,407 |
US Treasury Securities [Member] | Level 1 [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Short-term investments | 122,555 | 99,738 |
Restricted cash | 3,412 | 3,407 |
US Treasury Securities [Member] | Level 2 [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Short-term investments | 0 | 0 |
US Treasury Securities [Member] | Level 3 [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Short-term investments | 0 | 0 |
US Treasury Securities [Member] | Total [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Short-term investments | 122,555 | 99,738 |
Restricted cash | 3,412 | 3,407 |
US Government Agencies Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Short-term investments | 34,600 | 29,534 |
US Government Agencies Securities [Member] | Level 1 [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Short-term investments | 0 | 0 |
US Government Agencies Securities [Member] | Level 2 [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Short-term investments | 34,600 | 29,534 |
US Government Agencies Securities [Member] | Level 3 [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Short-term investments | 0 | 0 |
US Government Agencies Securities [Member] | Total [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Short-term investments | 34,600 | 29,534 |
FDIC-backed certificates of deposit [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Short-term investments | 12,880 | 10,236 |
FDIC-backed certificates of deposit [Member] | Level 1 [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Short-term investments | 0 | 0 |
FDIC-backed certificates of deposit [Member] | Level 2 [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Short-term investments | 12,880 | 10,236 |
FDIC-backed certificates of deposit [Member] | Level 3 [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Short-term investments | 0 | 0 |
FDIC-backed certificates of deposit [Member] | Total [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Short-term investments | 12,880 | 10,236 |
Money Market Funds [Member] | Level 1 [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Cash and Cash Equivalents | 5,898 | 11,133 |
Money Market Funds [Member] | Level 2 [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Cash and Cash Equivalents | 0 | 0 |
Money Market Funds [Member] | Level 3 [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Cash and Cash Equivalents | 0 | 0 |
Money Market Funds [Member] | Total [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Cash and Cash Equivalents | $5,898 | $11,133 |