Fair Value Measurements - Additional Information (Detail) - USD ($)	6 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Fair Value Measurements Disclosure [Line Items]
Percentage of securities using market-based information	99.90%
Percentage of securities using model-based techniques	0.10%
Minimum reserves for commercial loan	$ 500,000
Impaired loans, carrying amount	86,783,000		$ 70,689,000
Allocated allowance for loan losses	6,900,000
Fair value of allocated allowance	10,200,000
Estimated costs to sell	200,000
Provision for fair value measurements included in allowance for loan losses	6,000,000
Carrying amount of OREO	7,300,000
Written down of OREO	5,800,000
Fair value of OREO	6,500,000
Estimated cost to sell OREO	800,000
Loss from OREO included in earnings	$ 1,500,000
Short-term borrowings approximate fair value for amounts that mature, days, less than	90 days
Fair Value, Measurements, Nonrecurring [Member]
Fair Value Measurements Disclosure [Line Items]
Impaired loans, carrying amount	$ 16,800,000
Allocated allowance for loan losses	10,153,000		3,828,000
Fair value of OREO	6,527,000		7,831,000
Equity Securities [Member]
Fair Value Measurements Disclosure [Line Items]
Transfer of equity security to non-marketable equity securities, included in other assets			$ 56,000
Assets Still Held [Member]
Fair Value Measurements Disclosure [Line Items]
Change in unrealized gains or losses included in earnings relating to assets still held	$ 0	$ 0