Business Combination and Asset Purchase - Additional Information (Detail)			3 Months Ended	6 Months Ended		12 Months Ended
	Jan. 01, 2019 USD ($) Office $ / shares shares	Dec. 13, 2013 USD ($)	Jun. 30, 2019 USD ($) Loan shares	Jun. 30, 2019 USD ($) shares	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($) shares
Business Acquisition [Line Items]
Common stock, shares outstanding | shares			12,230,000	12,230,000		10,400,000
Business combination, acquisition related costs				$ 1,246,000		$ 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		$ 4,074,000
Fair value of assets acquired			257,200,000	257,200,000
Gross principal and contractual interest			359,200,000	359,200,000
Acquisition expected to be uncollectible			4,700,000	$ 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	$ 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	$ 1,300,000
Fair value of Federal Home Loan Bank (FHLB) advances, amortization period				2 years 3 months 18 days
Carrying amount, allowance	$ 2,118,000		$ 96,000	$ 96,000
Number of commercial purchased credit impaired loans paid off | Loan			2
Credit loss related to commercial purchased credit impaired loans			$ 1,985,000	1,985,000
Amortization expense				364,000	$ 84,000
Amortization expense			727,000	727,000
Core Deposits [Member] | Custar [Member]
Business Acquisition [Line Items]
Recognition of core deposit intangible asset with acquired purchase		$ 1,170,000
Limberlost Bancshares, Inc. [Member]
Business Acquisition [Line Items]
Common stock issued in exchange of each outstanding share | shares	1,830,000
Total consideration for acquisition	$ 78,902,000			78,902,000
Cash paid for acquisition				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
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				182,300		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				145,100
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			$ 3,500,000
Limberlost Bancshares, Inc. [Member]
Business Acquisition [Line Items]
Common stock issued in exchange of each outstanding share | shares	1,830
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	$ 78,900,000
Cash paid for acquisition	8,500,000			$ 8,465,000
Stock issued for acquisition	$ 70,400,000