Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2017 USD ($) Segment shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($) shares
Summary Of Significant Accounting Policies [Line Items]
Number of reportable operating segment | Segment	1
Period of delinquent loan	90 days
Advertising costs	$ 2,243,000	$ 1,799,000	$ 1,580,000
Number of nonqualified options or restricted stock for key employees and independent director | shares	500,000
Description of award terms	For key employees, the plan vesting schedule is one-fourth of granted stock-based awards per year beginning one year after the grant date with 100% vested on the fourth anniversary. For independent directors, the vesting schedule is one-third of granted stock-based awards per year beginning one year after the grant date with 100% vested on the third anniversary.
Unrecognized compensation cost related to nonvested stock options granted	$ 0	$ 0
Stock options, granted | shares	0	0	0
Shares granted, restricted common stock | shares	39,673	52,750	48,300
Compensation expense restricted stock awards	$ 928,000	$ 820,000	$ 621,000
Average amount of non interest bearing reserve with federal reserve bank	$ 50,000	$ 50,000
Independent Directors [Member]
Summary Of Significant Accounting Policies [Line Items]
Starting period of vesting of stock based award	1 year
Aggregate percentage of stock based awards to be matured	100.00%
Stock incentive plan, vesting per year	33.33%
Award vesting period	3 years
Key Employees [Member]
Summary Of Significant Accounting Policies [Line Items]
Starting period of vesting of stock based award	1 year
Aggregate percentage of stock based awards to be matured	100.00%
Stock incentive plan, vesting per year	25.00%
Award vesting period	4 years
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Percentage of tax benefit realized	50.00%
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Period of Consumer loans charged off	180 days
Premises and Equipment [Member] | Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Useful lives of premises and equipment	3 years
Premises and Equipment [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Useful lives of premises and equipment	39 years
Furniture, Fixtures and Equipment [Member] | Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Useful lives of premises and equipment	3 years
Furniture, Fixtures and Equipment [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Useful lives of premises and equipment	10 years
Buildings and Building Improvements [Member] | Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Useful lives of premises and equipment	15 years
Buildings and Building Improvements [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Useful lives of premises and equipment	39 years
Core Deposit [Member] | FC Banc Corp [Member]
Summary Of Significant Accounting Policies [Line Items]
Amortization of intangible assets	7 years
Core Deposit [Member] | Lake National Bank of Mentor, Ohio [Member]
Summary Of Significant Accounting Policies [Line Items]
Amortization of intangible assets	4 years