Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017
Assets:
Available-for-sale securities	$ 53,518	$ 2,670
Fair Value, Measurements, Recurring
Assets:
Available-for-sale securities	53,518	2,670
Foreign exchange contracts	170	4
Total Assets	104,260	2,719
Liabilities:
Foreign exchange contracts	177	146
Term loan	196,071
Total Liabilities	196,248	146
Fair Value, Measurements, Recurring | Cash equivalents
Assets:
Cash and cash equivalents	50,572	45
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Assets:
Total Assets	50,572	42
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring | Cash equivalents
Assets:
Cash and cash equivalents	50,572	42
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Assets:
Available-for-sale securities	53,518	2,670
Foreign exchange contracts	170	4
Total Assets	53,688	2,677
Liabilities:
Foreign exchange contracts	177	146
Term loan	196,071
Total Liabilities	$ 196,248	146
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Cash equivalents
Assets:
Cash and cash equivalents		$ 3