Fair Value Measurements (Assets Measured at Fair Value on a Recurring Basis) (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands | Dec. 31, 2016 | Sep. 30, 2016 |
Quoted Prices in Active Markets for Identical Assets (Level 1) | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Total assets at fair value on a recurring basis | $ 97,271 | $ 109,163 |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Money market funds | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Total assets at fair value on a recurring basis | 97,271 | 108,963 |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate bonds | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Total assets at fair value on a recurring basis | | 200 |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Commercial Paper [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Total assets at fair value on a recurring basis | | 0 |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Municipal bonds | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Total assets at fair value on a recurring basis | 0 | 0 |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Certificates of deposit | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Total assets at fair value on a recurring basis | 0 | 0 |
Significant Other Observable Inputs (Level 2) | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Total assets at fair value on a recurring basis | 968 | 3,992 |
Significant Other Observable Inputs (Level 2) | Money market funds | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Total assets at fair value on a recurring basis | 0 | 0 |
Significant Other Observable Inputs (Level 2) | Corporate bonds | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Total assets at fair value on a recurring basis | | 0 |
Significant Other Observable Inputs (Level 2) | Commercial Paper [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Total assets at fair value on a recurring basis | | 2,501 |
Significant Other Observable Inputs (Level 2) | Municipal bonds | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Total assets at fair value on a recurring basis | 221 | 744 |
Significant Other Observable Inputs (Level 2) | Certificates of deposit | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Total assets at fair value on a recurring basis | 747 | 747 |
Significant Unobservable Inputs (Level 3) | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Total assets at fair value on a recurring basis | 0 | 0 |
Significant Unobservable Inputs (Level 3) | Money market funds | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Total assets at fair value on a recurring basis | 0 | 0 |
Significant Unobservable Inputs (Level 3) | Corporate bonds | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Total assets at fair value on a recurring basis | | 0 |
Significant Unobservable Inputs (Level 3) | Commercial Paper [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Total assets at fair value on a recurring basis | | 0 |
Significant Unobservable Inputs (Level 3) | Municipal bonds | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Total assets at fair value on a recurring basis | 0 | 0 |
Significant Unobservable Inputs (Level 3) | Certificates of deposit | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Total assets at fair value on a recurring basis | 0 | 0 |
Estimate of Fair Value Measurement [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Total assets at fair value on a recurring basis | 98,239 | 113,155 |
Estimate of Fair Value Measurement [Member] | Money market funds | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Total assets at fair value on a recurring basis | 97,271 | 108,963 |
Estimate of Fair Value Measurement [Member] | Corporate bonds | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Total assets at fair value on a recurring basis | | 200 |
Estimate of Fair Value Measurement [Member] | Commercial Paper [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Total assets at fair value on a recurring basis | | 2,501 |
Estimate of Fair Value Measurement [Member] | Municipal bonds | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Total assets at fair value on a recurring basis | 221 | 744 |
Estimate of Fair Value Measurement [Member] | Certificates of deposit | | |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | | |
Total assets at fair value on a recurring basis | $ 747 | $ 747 |