Revenue (Schedule of Accounts Receivable) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Sep. 30, 2020
Contract With Customer Asset [Line Items]
Total billed receivables	$ 312,628	$ 364,554
Current unbilled receivables (contract assets)	204,592	181,792
Less: Allowance for uncollectible amounts	(7,499)	(8,359)
Total accounts receivable, net	509,721	537,987
Trade Accounts Receivable [Member]
Contract With Customer Asset [Line Items]
Billed receivables	265,732	307,914
Other (Chinese Financial Institutions) [Member]
Contract With Customer Asset [Line Items]
Billed receivables	$ 46,896	$ 56,640