Restructuring costs - Rollforward of restructuring liability (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Restructuring liability
Accrued costs	$ 1,575	$ 1,992
Employee Separation and other
Restructuring liability
Balance as of the beginning of the period	2,000
Accrued costs	(600)
Cash payments	(2,000)
Balance as of the end of the period	600
Consulting Costs
Restructuring liability
Balance as of the beginning of the period	800
Accrued costs	(1,000)
Cash payments	$ (1,800)