Contract Balance - Receivables (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Sep. 30, 2023
Revenue from Contract with Customer [Abstract]
Billed	$ 225,447	$ 234,745
Unbilled	189,930	203,896
Receivables Gross	415,377	438,641
Less: allowance for doubtful accounts	(5,406)	(4,978)
Accounts Receivable, after Allowance for Credit Loss	409,971	433,663
Less: long-term receivables	(42,493)	(45,716)
Accounts receivable, net	$ 367,478	$ 387,947