Contract Balances and Performance Obligation - Receivables (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Sep. 30, 2019
Revenue from Contract with Customer [Abstract]
Accounts Receivable, after Allowance for Credit Loss, Noncurrent	$ (35,981)	$ (34,370)
Accounts receivable, net	281,640	297,427
Accounts Receivable, before Allowance for Credit Loss	186,330	206,714
Unbilled Receivables, Current	134,334	127,651
Receivables Gross	320,664	334,365
Accounts Receivable, Allowance for Credit Loss	(3,043)	(2,568)
Accounts Receivable, after Allowance for Credit Loss	$ 317,621	$ 331,797