Receivables - Activity of Allowance for Doubtful Accounts (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance, beginning of year	$ 2,126	$ 2,927
Add: expense	2,011	0	$ 1,485
Less: write-offs (net of recoveries)	(1,945)	(801)
Balance, end of year	$ 2,192	$ 2,126	$ 2,927