Fair Value Measurements - Cash Equivalents (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Sep. 30, 2019	Sep. 30, 2018
Cash equivalents
Assets:
Cash equivalents	$ 16,164	$ 50,572
Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash equivalents
Assets:
Cash equivalents	6,188	50,572
Quoted Prices in Active Markets for Identical Assets (Level 1) | Money market funds
Assets:
Cash equivalents	6,200	$ 50,600
Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents	10,000
Significant Other Observable Inputs (Level 2) | Cash equivalents
Assets:
Cash equivalents	$ 9,976