Restructuring costs - Rollforward of restructuring liability (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Restructuring liability
Accrued costs	$ 3,807	$ 1,757	$ 5,382	$ 3,749
Employee Separation and other
Restructuring liability
Balance as of the beginning of the period			2,000
Accrued costs			4,000
Cash payments			(5,000)
Balance as of the end of the period	1,000		1,000
Consulting Costs
Restructuring liability
Balance as of the beginning of the period			800
Accrued costs			1,400
Cash payments			(2,000)
Balance as of the end of the period	$ 200		$ 200