Contract Balances and Performance Obligations - Receivables (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Accounts Receivable, after Allowance for Credit Loss [Abstract]
Billed Receivables	$ 206,714	$ 196,960
Unbilled Receivables	127,651	73,221
Receivables Gross	334,365	270,181
Allowance for doubtful accounts	(2,568)	(3,439)	$ (2,941)
Net receivables	331,797	266,742
Accounts receivable, net	297,427	266,742
Accounts Receivable, net , noncurrent		34,400
Expense, Allowance for Credit Loss	518	623
Write-off	$ (1,389)	$ (125)