Short-Term Borrowings - Summary of Federal Funds Purchased and Other Short-term Borrowings (Detail) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Federal Funds Purchased [Member]
Short-term Debt [Line Items]
Average balance		$ 41,000
Average rate paid		0.54%
Short Term Borrowings [Member]
Short-term Debt [Line Items]
Outstanding balance	$ 37,800,000	$ 42,700,000
Maximum indebtedness	50,300,000	42,700,000
Average balance	$ 10,609,000	$ 1,951,000
Average rate paid	0.17%	0.19%
Interest rate on balance	0.15%	0.14%