Segment Information - Reconciliation of Reportable Segment Assets to Corresponding Consolidated Amounts (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Cash, cash equivalents and marketable securities	$ 263,275	$ 342,140
Deferred tax asset	3,489	5,064
Assets	1,503,917	1,515,999
Reportable Segments
Segment Reporting Information [Line Items]
Assets	$ 1,237,153	$ 1,168,795