Revenue from Contracts with Customers - Contract Balances (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Sep. 30, 2020
Accounts Receivable, after Allowance for Credit Loss, Current [Abstract]
Accounts receivable, net	$ 196,679		$ 188,291
Contract with Customer, Asset, after Allowance for Credit Loss, Current [Abstract]
Contract assets	$ 12,900		16,800
Capitalized Contract Cost [Abstract]
Sales commission amortization period	60 months
Deferred commissions	$ 400		400
Deferred commission amortization expense		$ 100
Contract with Customer, Liability [Abstract]
Current contract liabilities	35,661		31,357
Contract liabilities	35,700		$ 31,400
Revenue recognized	12,600
Maximum
Capitalized Contract Cost [Abstract]
Deferred commission amortization expense	$ 100