Investment Securities - Schedule of Unrealized Losses and Fair Value by Investment Category for Securities Held to Maturity (Detail)	Sep. 30, 2016 USD ($)	Dec. 31, 2015 USD ($) Security
Schedule of Held-to-maturity Securities [Line Items]
Count | Security		10
Less than 12 Months, Fair Value		$ 13,289,000
Less than 12 Months, Unrealized Losses		(78,000)
12 Months or More, Fair Value		3,897,000
12 Months or More, Unrealized Losses		(82,000)
Total, Fair Value		17,186,000
Total, Unrealized Losses	$ 0	$ (160,000)
Obligations of other U.S. government agencies and corporations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Count | Security		2
Less than 12 Months, Fair Value		$ 1,958,000
Less than 12 Months, Unrealized Losses		(36,000)
12 Months or More, Fair Value		1,965,000
12 Months or More, Unrealized Losses		(28,000)
Total, Fair Value		3,923,000
Total, Unrealized Losses		$ (64,000)
Obligations of state and political subdivisions [Member]
Schedule of Held-to-maturity Securities [Line Items]
Count | Security		1
Less than 12 Months, Fair Value		$ 6,862,000
Less than 12 Months, Unrealized Losses		(5,000)
Total, Fair Value		6,862,000
Total, Unrealized Losses		$ (5,000)
Residential mortgage-backed securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Count | Security		7
Less than 12 Months, Fair Value		$ 4,469,000
Less than 12 Months, Unrealized Losses		(37,000)
12 Months or More, Fair Value		1,932,000
12 Months or More, Unrealized Losses		(54,000)
Total, Fair Value		6,401,000
Total, Unrealized Losses		$ (91,000)