Securities Sold Under Agreement to Repurchase and Other Borrowings - Additional Information (Detail) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Schedule of Held-to-maturity Securities [Line Items]
Securities sold under agreement to repurchase, Amount	$ 197,000
Other borrowings, Amount	0	$ 512,000
U.S. Agency Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities sold under agreement to repurchase, Amount	$ 4,900,000	$ 0