Business Combinations - Carrying Value of Loans Acquired (Detail) - USD ($) $ in Thousands	Oct. 23, 2020	Feb. 08, 2019
Almena State Bank [Member]
Business Acquisition [Line Items]
Fair value of acquired loans	$ 31,407
Almena State Bank [Member] | Commercial Real Estate [Member]
Business Acquisition [Line Items]
Fair value of acquired loans	5,491
Almena State Bank [Member] | Commercial and Industrial [Member]
Business Acquisition [Line Items]
Fair value of acquired loans	6,140
Almena State Bank [Member] | Residential Real Estate [Member]
Business Acquisition [Line Items]
Fair value of acquired loans	3,339
Almena State Bank [Member] | Agricultural Real Estate [Member]
Business Acquisition [Line Items]
Fair value of acquired loans	4,122
Almena State Bank [Member] | Consumer [Member]
Business Acquisition [Line Items]
Fair value of acquired loans	1,769
Almena State Bank [Member] | Agricultural [Member]
Business Acquisition [Line Items]
Fair value of acquired loans	10,546
Almena State Bank [Member] | Non Credit Impaired Loans [Member]
Business Acquisition [Line Items]
Fair value of acquired loans	25,447
Almena State Bank [Member] | Non Credit Impaired Loans [Member] | Commercial Real Estate [Member]
Business Acquisition [Line Items]
Fair value of acquired loans	3,895
Almena State Bank [Member] | Non Credit Impaired Loans [Member] | Commercial and Industrial [Member]
Business Acquisition [Line Items]
Fair value of acquired loans	5,848
Almena State Bank [Member] | Non Credit Impaired Loans [Member] | Residential Real Estate [Member]
Business Acquisition [Line Items]
Fair value of acquired loans	3,157
Almena State Bank [Member] | Non Credit Impaired Loans [Member] | Agricultural Real Estate [Member]
Business Acquisition [Line Items]
Fair value of acquired loans	3,226
Almena State Bank [Member] | Non Credit Impaired Loans [Member] | Consumer [Member]
Business Acquisition [Line Items]
Fair value of acquired loans	1,769
Almena State Bank [Member] | Non Credit Impaired Loans [Member] | Agricultural [Member]
Business Acquisition [Line Items]
Fair value of acquired loans	7,552
Almena State Bank [Member] | Purchase Credit Impaired Loans [Member]
Business Acquisition [Line Items]
Fair value of acquired loans	5,960
Almena State Bank [Member] | Purchase Credit Impaired Loans [Member] | Commercial Real Estate [Member]
Business Acquisition [Line Items]
Fair value of acquired loans	1,596
Almena State Bank [Member] | Purchase Credit Impaired Loans [Member] | Commercial and Industrial [Member]
Business Acquisition [Line Items]
Fair value of acquired loans	292
Almena State Bank [Member] | Purchase Credit Impaired Loans [Member] | Residential Real Estate [Member]
Business Acquisition [Line Items]
Fair value of acquired loans	182
Almena State Bank [Member] | Purchase Credit Impaired Loans [Member] | Agricultural Real Estate [Member]
Business Acquisition [Line Items]
Fair value of acquired loans	896
Almena State Bank [Member] | Purchase Credit Impaired Loans [Member] | Agricultural [Member]
Business Acquisition [Line Items]
Fair value of acquired loans	$ 2,994
MidFirst Bank [Member]
Business Acquisition [Line Items]
Fair value of acquired loans		$ 6,507
MidFirst Bank [Member] | Commercial Real Estate [Member]
Business Acquisition [Line Items]
Fair value of acquired loans		668
MidFirst Bank [Member] | Commercial and Industrial [Member]
Business Acquisition [Line Items]
Fair value of acquired loans		34
MidFirst Bank [Member] | Residential Real Estate [Member]
Business Acquisition [Line Items]
Fair value of acquired loans		3,271
MidFirst Bank [Member] | Consumer [Member]
Business Acquisition [Line Items]
Fair value of acquired loans		2,534
MidFirst Bank [Member] | Non Credit Impaired Loans [Member]
Business Acquisition [Line Items]
Fair value of acquired loans		6,507
MidFirst Bank [Member] | Non Credit Impaired Loans [Member] | Commercial Real Estate [Member]
Business Acquisition [Line Items]
Fair value of acquired loans		668
MidFirst Bank [Member] | Non Credit Impaired Loans [Member] | Commercial and Industrial [Member]
Business Acquisition [Line Items]
Fair value of acquired loans		34
MidFirst Bank [Member] | Non Credit Impaired Loans [Member] | Residential Real Estate [Member]
Business Acquisition [Line Items]
Fair value of acquired loans		3,271
MidFirst Bank [Member] | Non Credit Impaired Loans [Member] | Consumer [Member]
Business Acquisition [Line Items]
Fair value of acquired loans		$ 2,534