Fair Value Measures - Changes in Fair Value of Contingent Earn-Out Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Contingent and deferred acquisition payments	$ 17,470	$ 14,211
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	4,000	8,648
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Earn-out Liability	1,500	2,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements		(8,188)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	(2,550)
Charges (credits) to acquisition-related costs, net	(25)	1,540
Ending balance	2,925	$ 4,000
Maximum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Contingent and deferred acquisition payments	$ 4,800