Details of Selected Consolidated Balance Sheet Captions - Accounts Receivables Detail Table (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017
Condensed Balance Sheet Statements, Captions [Line Items]
Total accounts receivable	$ 268,090	$ 233,128
Less: allowance for doubtful accounts	14,795	10,865
Net accounts receivable	253,295	222,263
Billed and Unbilled Receivables | Billed accounts receivable
Condensed Balance Sheet Statements, Captions [Line Items]
Total accounts receivable	138,794	135,091
Billed and Unbilled Receivables | Unbilled revenue
Condensed Balance Sheet Statements, Captions [Line Items]
Total accounts receivable	81,005	73,143
Other accounts receivable
Condensed Balance Sheet Statements, Captions [Line Items]
Total accounts receivable	$ 48,291	$ 24,894