Summary of Significant Accounting Policies - Carrying Amount of Goodwill and Intangible Assets (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Goodwill
Balance at beginning of year	$ 13,801	$ 10,259
Goodwill acquired		3,542
Balance at end of year	13,801	13,801	$ 10,259
Intangible assets
Balance at beginning of year	2,487	1,759
Intangible assets acquired		1,491
Amortization	(643)	(763)	(637)
Balance at end of year	$ 1,844	$ 2,487	$ 1,759