Business Combination & Asset Purchase - Additional Information (Detail)				3 Months Ended	12 Months Ended
	Nov. 16, 2020 USD ($) shares	Jan. 01, 2019 USD ($) Office $ / shares shares	Dec. 13, 2013 USD ($)	Jun. 30, 2019 Loan	Dec. 31, 2020 USD ($) shares	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($)	Nov. 30, 2020 USD ($) Client	Jan. 01, 2020 USD ($)
Business Acquisition [Line Items]
Common stock, shares outstanding | shares					12,230,000	12,230,000
Business combination, acquisition related costs						$ 1,280,000	$ 742,100
Business combination, acquisition related costs percentage							98.40%
Recognition of core deposit intangible asset with acquired purchase						$ 3,900,000
Remaining economic useful life						7 years
Goodwill					$ 47,340,000	$ 47,340,000
Fair value of assets acquired					257,200,000
Gross principal and contractual interest					359,200,000
Acquisition expected to be uncollectible					$ 4,700,000
Loan receivable weighted average life					70 months
Business combination, premises and equipment written down value					$ 1,200,000
Business combination, average remaining life					16 years 9 months
Fair value for certificate of deposit, valuation amount					$ 500,000
Fair value for certificate of deposit, amortization period					1 year 6 months
Fair value of Federal Home Loan Bank (FHLB) advances, valuation amount					$ 1,300,000
Fair value of Federal Home Loan Bank (FHLB) advances, amortization period					2 years 3 months 18 days
Fair value adjustment of loans acquired and accounted		$ 2,118,000			$ 0	62,000			$ 62,000
Number of commercial purchased credit impaired loans paid off | Loan				2
Discount recognized at acquisition related to commercial purchased credit-impaired loans						1,985,000
Amortization expense					720,000	727,000	$ 167,000
Core Deposits [Member] | Custar [Member]
Business Acquisition [Line Items]
Recognition of core deposit intangible asset with acquired purchase			$ 1,170,000
Customer Lists [Member]
Business Acquisition [Line Items]
Amortization expense					$ 16,000
Consulting Fees [Member]
Business Acquisition [Line Items]
Business combination, acquisition related costs						19,300	340,000
Other General and Administrative Expenses [Member]
Business Acquisition [Line Items]
Business combination, acquisition related costs						199,800	331,500
Data Processing [Member]
Business Acquisition [Line Items]
Business combination, acquisition related costs						867,600	$ 58,600
Employee Benefits [Member]
Business Acquisition [Line Items]
Business combination, acquisition related costs						163,000.0
ATM Expense [Member]
Business Acquisition [Line Items]
Business combination, acquisition related costs						31,400
Bank of Geneva [Member]
Business Acquisition [Line Items]
Number of full-service offices | Office		6
Pro-forma operating revenue, net of tax						7,400,000
Limberlost Bancshares, Inc. [Member]
Business Acquisition [Line Items]
Common stock issued in exchange of each outstanding share | shares		1,830,000
Cash payment for exchange of each share | $ / shares		$ 8,465.00
Common stock, shares outstanding | shares		1,000
Share price | $ / shares		$ 38.49
Total consideration for acquisition		$ 78,902,000
Cash paid for acquisition		8,465,000				$ 8,465,000
Stock issued for acquisition		70,437,000
Goodwill		43,266,000
Limberlost Bancshares, Inc. [Member] | Core Deposits [Member]
Business Acquisition [Line Items]
Recognition of core deposit intangible asset with acquired purchase		$ 3,900,000
Remaining economic useful life		7 years
Adams County Financial Resources
Business Acquisition [Line Items]
Common stock issued in exchange of each outstanding share | shares	40,049
Total consideration for acquisition	$ 825,000
Stock issued for acquisition	825,000
Assets under management amount								$ 83,000
Number of clients assets under management | Client								450
Increase to noninterest income	500,000
Adams County Financial Resources | Customer Lists [Member]
Business Acquisition [Line Items]
Recognition of core deposit intangible asset with acquired purchase	$ 800,000
Remaining economic useful life	6 years 6 months