Short-Term Borrowings - Summary of Federal Funds Purchased and Other Short-term Borrowings are Included in Federal Home Loan Bank Advances on Consolidated Balance Sheets (Detail) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Federal Funds Purchased [Member]
Short-term Debt [Line Items]
Maximum indebtedness		$ 20,000,000
Average balance		$ 116,000
Average rate paid		0.86%
Short Term Borrowings [Member]
Short-term Debt [Line Items]
Outstanding balance	$ 48,300,000	$ 31,000,000
Maximum indebtedness	106,300,000	70,400,000
Average balance	$ 27,294,000	$ 10,483,000
Average rate paid	0.94%	0.42%
Interest rate on balance	1.17%	0.64%