Receivables - Summary of Receivables (Detail) - USD ($) $ in Thousands		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Receivables [Abstract]
Billed		$ 114,464	$ 123,083
Unbilled	[1]	46,435	35,139
Receivables, Gross, Current, Total		160,899	158,222
Less: allowance for doubtful accounts		(2,126)	(2,927)	$ (3,157)
Receivables, net		$ 158,773	$ 155,295

[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.