Restructuring Costs - Rollforward of Restructuring Liability (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Restructuring liability
Accrued costs	$ 7,746	$ 3,807	$ 11,881	$ 5,382
Employee Separation and Other
Restructuring liability
Balance as of the beginning of the period			5,200
Accrued costs			6,900
Cash payments			(8,300)
Balance as of the end of the period	3,800		3,800
Consulting Costs
Restructuring liability
Balance as of the beginning of the period			800
Accrued costs			5,000
Cash payments			(2,500)
Balance as of the end of the period	$ 3,300		$ 3,300