Fair Value Measurement - Additional Information (Detail) $ in Thousands	6 Months Ended	12 Months Ended
	Mar. 31, 2018 USD ($) Loan	Sep. 30, 2017 USD ($) Loan
Fair Value Disclosures [Abstract]
Number of impaired loans | Loan	140	164
Impaired loans, carrying value	$ 13,900	$ 15,600
Impaired loans, valuation allowance	304	345
Impaired loans, net fair value	$ 13,600	$ 15,200