Fair Value Measurements (Details) - USD ($) $ in Thousands	6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Sep. 30, 2019
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Exchangeable notes, fair value	$ 107,469
Accrued Contingent Consideration
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning	18,226	$ 5,999
Contingent consideration accrued at time of business combination	0	4,605
Change in the fair value of warrant liabilities, included in Other expenses	12	2,153
Contingent consideration paid	(6,477)	(4,194)
Balance, ending	11,761	$ 8,563
Accrued Expenses and Other Current Liabilities
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Contingent consideration	8,484		$ 10,223
Other Long-term Liabilities
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Contingent consideration	$ 3,277		$ 8,003