Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
	Oct. 01, 2016	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Income Tax Contingency [Line Items]
Gross liability for unrecognized tax benefits		$ 353				$ 493				$ 353	$ 493
Unrecognized tax benefits that would impact effective tax rate		200				300				200	300
Decrease related to prior year tax positions										140
Net liability for accrued interest and penalties		140								140
Income tax expense (benefits)		$ 2,090	$ 2,032	$ 2,205	$ 1,980	$ 2,121	$ 1,961	$ 1,861	$ 2,250	$ 8,307	$ 8,193	$ 7,414
ASU 2016-09 [Member] | New Accounting Pronouncement Early Adoption Effect [Member]
Income Tax Contingency [Line Items]
Income tax expense (benefits)	$ (400)			$ (4)	$ (200)