Restructuring - Rollforward of restructuring liability (Details) - USD ($)	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Restructuring liability
Accrued costs	$ 15,386,000	$ 5,018,000	$ 2,260,000
Employee Separation and other
Restructuring liability
Balance as of the beginning of the period	600	1,000.0
Accrued costs	7,500	4,200
Cash payments	(6,100)	(4,600)
Balance as of the end of the period	2,000.0	600	$ 1,000.0
Consulting Costs
Restructuring liability
Balance as of the beginning of the period	300
Accrued costs	7,900	800
Cash payments	(7,400)	(500)
Balance as of the end of the period	$ 800	$ 300