Fair Value Measurement - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Increase in fair value			$ 250,000
Derivative instrument maximum maturity period			30 years
Transfers between level 1 and level 2			$ 0		$ 0
Fair value of the collateral dependent loans, net carrying amount	$ 1,400,000	$ 8,200,000	1,400,000	$ 8,200,000	4,000,000
Specific allowance for collateral dependent loans	5,000	1,000,000	$ 5,000	1,000,000	1,300,000
Discount applied to appraisals for estimated selling costs percentage			10.00%
Mortgage servicing rights carried at fair value, valuation allowance net change during the period			$ 5,000	766,000
Net impairment reflected in other income	2,000	292,000	5,000	727,000
Other real estate owned carried at fair value	483,000	1,000,000	483,000	1,000,000	1,000,000
Valuation allowance related to other real estate owned	389,000	1,000,000	389,000	1,000,000	1,000,000
Recovery of expense	0	(27,000)	$ (38,000)	(26,000)
Maximum maturity period of short term borrowings			90 days
Collateral Dependent Loans [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Increase (decrease) in provision for loan losses	252,000	592,000	$ 479,000	3,600,000
Mortgage Servicing Rights [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Mortgage servicing rights carried at fair value	87,000	$ 2,800,000	87,000	$ 2,800,000
Construction [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value option, loans held as assets, aggregate amount in nonaccrual status	$ 0		$ 0		$ 0