Stock Options and Employee Stock Purchase Plan - Summary of Options Outstanding Segregated By Range (Detail) - $ / shares	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option Outstanding at September 30, 2015 (in shares)	1,602,822	1,449,409	1,240,941
Outstanding Options, Weighted Average Exercise Price (usd per share)	$ 9.51	$ 10.03	$ 10.31
Options Exercisable at September 30, 2015 (in shares)	1,062,837	885,777
Range I [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option Outstanding at September 30, 2015 (in shares)	1,245,264
Option Outstanding, Weighted Average Remaining Contractual Life	6 years 8 months 12 days
Outstanding Options, Weighted Average Exercise Price (usd per share)	$ 8.17
Options Exercisable at September 30, 2015 (in shares)	773,336
Options Exercisable, Weighted Average Exercise Price	$ 8.15
Exercise Price, Lower range	4.50
Exercise Price, Upper range	$ 9.87
Range II [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option Outstanding at September 30, 2015 (in shares)	330,900
Option Outstanding, Weighted Average Remaining Contractual Life	5 years 5 months 25 days
Outstanding Options, Weighted Average Exercise Price (usd per share)	$ 12.33
Options Exercisable at September 30, 2015 (in shares)	262,843
Options Exercisable, Weighted Average Exercise Price	$ 12.79
Exercise Price, Lower range	10.00
Exercise Price, Upper range	$ 15.50
Range III [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option Outstanding at September 30, 2015 (in shares)	26,658
Option Outstanding, Weighted Average Remaining Contractual Life	4 months 17 days
Outstanding Options, Weighted Average Exercise Price (usd per share)	$ 37.18
Options Exercisable at September 30, 2015 (in shares)	26,658
Options Exercisable, Weighted Average Exercise Price	$ 37.18
Exercise Price, Lower range	21.40
Exercise Price, Upper range	$ 46.90