Stock-Based Compensation Plans - Schedule of Fair Value at the Date of Grant (Detail)	12 Months Ended
	Sep. 30, 2017 shares
Fiscal 2015 (2015 - 2017) [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Minimum Shares	8,440
Target Shares	42,199
Maximum Shares	84,398
Fiscal 2016 (2016 - 2018) [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Minimum Shares	13,268
Target Shares	66,338
Maximum Shares	132,676
Fiscal 2017 (2017 - 2019) [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Minimum Shares	10,437
Target Shares	52,185
Maximum Shares	104,370