Receivables - Summary of Receivables (Detail) - USD ($) $ in Thousands		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Receivables [Abstract]
Billed		$ 124,731	$ 114,464
Unbilled	[1]	45,247	46,435
Receivables, Gross, Current, Total		169,978	160,899
Less: allowance for doubtful accounts		(2,192)	(2,126)	$ (2,927)
Receivables, net		$ 167,786	$ 158,773

[1] Represents revenue recorded in excess of amounts billable pursuant to contract provisions and generally become billable at contractually specified dates or upon the attainment of milestones. Unbilled amounts are expected to be realized within one year.