Pension and Other Post-Retirement Plans - Additional Information (Detail) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Other non-interest expense	$ 7,837,000	$ 10,138,000	$ 4,207,000	$ 3,899,000	$ 4,107,000	$ 4,369,000	$ 4,122,000	$ 3,987,000		$ 3,188,000	$ 2,697,000
401(k) Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Description of employees eligibility										The Company has a 401(k) Plan whereby each employee reaching the age of 21 automatically becomes a participant in the plan. Employees may contribute up to 15% of their compensation subject to certain limits based on federal tax laws. All employees who have worked for one year or 1,000 hours are eligible for an automatic employer contribution of 3% of employees’ compensation, which includes no vesting period.
Minimum age of employee to become participant										21 years
Maximum annual contributions per employee, percent										15.00%
Minimum number of year worked by employees										1 year
Minimum number of hours worked by employees										1000 hours
Employer contribution percentage on employees compensation										3.00%
Automatic employer matching contributions vesting period										0 years
Employer matching contribution, percent										50.00%
Employer match of eligible employees contributions percentage										2.00%
Employer matching contributions vesting period										4 years
Contribution expense										$ 479,000	$ 282,000
401(k) Plan [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contribution percentage on employees compensation										4.00%
Defined Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate											3.25%
Expected return on plan assets											0.00%
Supplemental Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate										3.35%	4.00%
Accrued benefits	654,000				700,000					$ 654,000	$ 700,000
Other non-interest expense										54,000	55,000
Other non-interest income										486,000
Other non-interest expense										59,000
Supplemental Retirement Plan [Member] | Scenario Forecast [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected Contributions to the plan									$ 201,000
Endorsement Split-Dollar Life Insurance Arrangements [Member]
Defined Benefit Plan Disclosure [Line Items]
Accrued benefits	$ 397,000				$ 489,000					397,000	489,000
Other non-interest expense											117,000
Post-retirement benefit expense										$ 26,000	143,000
Other non-interest income											$ 402,000