Revenue from Contracts with Customers - Contract Balances (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Mar. 31, 2020	Mar. 31, 2020	Sep. 30, 2019
Accounts Receivable, after Allowance for Credit Loss, Current [Abstract]
Accounts receivable, net	$ 179,014	$ 179,014	$ 165,602
Contract with Customer, Asset, Net, Current [Abstract]
Contract assets	$ 15,100	$ 15,100	14,000
Capitalized Contract Cost [Abstract]
Sales commission amortization period	60 months	60 months
Deferred commissions	$ 600	$ 600	800
Deferred commission amortization expense	100	300
Contract with Customer, Liability [Abstract]
Current contract liabilities	29,090	29,090	29,435
Contract liabilities	29,100	$ 29,100	$ 29,400
Revenue recognized	$ 10,100