Fair Value of Financial Assets and Liabilities - Summary of Fair Value of Financial Assets and Liabilities (Details) - USD ($) $ in Thousands | Jul. 31, 2015 | Apr. 30, 2015 |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents: | $ 53,450 | $ 54,041 |
Short-term investments: | 49,696 | 52,730 |
Fair value, measurements, recurring | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents: | 12,577 | 4,064 |
Short-term investments: | 49,696 | 52,730 |
Total assets | 62,273 | 56,794 |
Fair value, measurements, recurring | Fair value, inputs, level 1 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents: | 4,210 | 2,831 |
Short-term investments: | 33,789 | 28,808 |
Total assets | 37,999 | 31,639 |
Fair value, measurements, recurring | Fair value, inputs, level 2 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents: | 8,367 | 1,233 |
Short-term investments: | 15,907 | 23,922 |
Total assets | 24,274 | 25,155 |
Fair value, measurements, recurring | Fair value, inputs, level 3 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents: | 0 | 0 |
Short-term investments: | 0 | 0 |
Total assets | 0 | 0 |
Certificates of deposit | Fair value, measurements, recurring | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Short-term investments: | 4,510 | 4,004 |
Certificates of deposit | Fair value, measurements, recurring | Fair value, inputs, level 1 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Short-term investments: | 0 | 0 |
Certificates of deposit | Fair value, measurements, recurring | Fair value, inputs, level 2 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Short-term investments: | 4,510 | 4,004 |
Certificates of deposit | Fair value, measurements, recurring | Fair value, inputs, level 3 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Short-term investments: | 0 | 0 |
Municipal bonds | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents: | 1,597 | 102 |
Municipal bonds | Fair value, measurements, recurring | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents: | 1,597 | 102 |
Short-term investments: | 641 | 4,565 |
Municipal bonds | Fair value, measurements, recurring | Fair value, inputs, level 1 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents: | 0 | 0 |
Short-term investments: | 0 | 0 |
Municipal bonds | Fair value, measurements, recurring | Fair value, inputs, level 2 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents: | 1,597 | 102 |
Short-term investments: | 641 | 4,565 |
Municipal bonds | Fair value, measurements, recurring | Fair value, inputs, level 3 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents: | 0 | 0 |
Short-term investments: | 0 | 0 |
Commercial paper | Fair value, measurements, recurring | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents: | 6,770 | 875 |
Short-term investments: | 3,798 | 6,273 |
Commercial paper | Fair value, measurements, recurring | Fair value, inputs, level 1 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents: | 0 | 0 |
Short-term investments: | 0 | 0 |
Commercial paper | Fair value, measurements, recurring | Fair value, inputs, level 2 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents: | 6,770 | 875 |
Short-term investments: | 3,798 | 6,273 |
Commercial paper | Fair value, measurements, recurring | Fair value, inputs, level 3 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents: | 0 | 0 |
Short-term investments: | 0 | 0 |
Corporate bonds | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents: | 0 | 256 |
Corporate bonds | Fair value, measurements, recurring | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents: | 0 | 256 |
Short-term investments: | 5,152 | 6,372 |
Corporate bonds | Fair value, measurements, recurring | Fair value, inputs, level 1 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents: | 0 | 0 |
Short-term investments: | 0 | 0 |
Corporate bonds | Fair value, measurements, recurring | Fair value, inputs, level 2 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents: | 0 | 256 |
Short-term investments: | 5,152 | 6,372 |
Corporate bonds | Fair value, measurements, recurring | Fair value, inputs, level 3 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents: | 0 | 0 |
Short-term investments: | 0 | 0 |
U.S. Treasury notes | Fair value, measurements, recurring | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Short-term investments: | 23,790 | 23,809 |
U.S. Treasury notes | Fair value, measurements, recurring | Fair value, inputs, level 1 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Short-term investments: | 23,790 | 23,809 |
U.S. Treasury notes | Fair value, measurements, recurring | Fair value, inputs, level 2 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Short-term investments: | 0 | 0 |
U.S. Treasury notes | Fair value, measurements, recurring | Fair value, inputs, level 3 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Short-term investments: | 0 | 0 |
U.S. Treasury bonds | Fair value, measurements, recurring | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Short-term investments: | 9,999 | 4,999 |
U.S. Treasury bonds | Fair value, measurements, recurring | Fair value, inputs, level 1 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Short-term investments: | 9,999 | 4,999 |
U.S. Treasury bonds | Fair value, measurements, recurring | Fair value, inputs, level 2 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Short-term investments: | 0 | 0 |
U.S. Treasury bonds | Fair value, measurements, recurring | Fair value, inputs, level 3 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Short-term investments: | 0 | 0 |
Corporate notes | Fair value, measurements, recurring | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Short-term investments: | 1,806 | 2,708 |
Corporate notes | Fair value, measurements, recurring | Fair value, inputs, level 1 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Short-term investments: | 0 | 0 |
Corporate notes | Fair value, measurements, recurring | Fair value, inputs, level 2 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Short-term investments: | 1,806 | 2,708 |
Corporate notes | Fair value, measurements, recurring | Fair value, inputs, level 3 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Short-term investments: | 0 | 0 |
Money market funds | Fair value, measurements, recurring | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents: | 4,210 | 2,831 |
Money market funds | Fair value, measurements, recurring | Fair value, inputs, level 1 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents: | 4,210 | 2,831 |
Money market funds | Fair value, measurements, recurring | Fair value, inputs, level 2 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents: | 0 | 0 |
Money market funds | Fair value, measurements, recurring | Fair value, inputs, level 3 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents: | $ 0 | $ 0 |