Recently Issued and Adopted Accounting Standards - 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
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
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]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Income tax expense (benefits)	$ (400)			$ (4)	$ (200)