Description of Business and Summary of Significant Accounting Policies - Schedule of Impact of ASC 326 Adoption on Allowance for Credit losses on Loans (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans	$ 91,366		$ 54,238	$ 51,389
Pre ASC 326 Adoption [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans		$ 54,238
ASC 326 [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans		51,043
ASC 326 [Member] | Impact of ASC Adoption [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans		(3,195)
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans	7,035		5,625
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member] | Pre ASC 326 Adoption [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans		5,625
Real Estate [Member] | Commercial Real Estate Non-Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans	11,842		8,358
Real Estate [Member] | Commercial Real Estate Non-Owner Occupied [Member] | Pre ASC 326 Adoption [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans		8,358
Real Estate [Member] | Construction and Development Less than 60 Months [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans	2,560		2,214
Real Estate [Member] | Construction and Development Less than 60 Months [Member] | Pre ASC 326 Adoption [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans		2,214
Real Estate [Member] | Construction Residential Real Estate Less than 60 Months [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans	627		1,933
Real Estate [Member] | Construction Residential Real Estate Less than 60 Months [Member] | Pre ASC 326 Adoption [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans		1,933
Real Estate [Member] | Residential Real Estate First Lien [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans	2,570		8,692
Real Estate [Member] | Residential Real Estate First Lien [Member] | Pre ASC 326 Adoption [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans		8,692
Real Estate [Member] | Residential Real Estate All Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans	2,230		2,767
Real Estate [Member] | Residential Real Estate All Other [Member] | Pre ASC 326 Adoption [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans		2,767
Real Estate [Member] | Farmland [Member] | Pre ASC 326 Adoption [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans		2,821
Real Estate [Member] | ASC 326 [Member] | Commercial Real Estate Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans		2,819
Real Estate [Member] | ASC 326 [Member] | Commercial Real Estate Owner Occupied [Member] | Impact of ASC Adoption [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans		(2,806)
Real Estate [Member] | ASC 326 [Member] | Commercial Real Estate Non-Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans		2,851
Real Estate [Member] | ASC 326 [Member] | Commercial Real Estate Non-Owner Occupied [Member] | Impact of ASC Adoption [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans		(5,507)
Real Estate [Member] | ASC 326 [Member] | Construction and Development Less than 60 Months [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans		1,158
Real Estate [Member] | ASC 326 [Member] | Construction and Development Less than 60 Months [Member] | Impact of ASC Adoption [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans		(1,056)
Real Estate [Member] | ASC 326 [Member] | Construction Residential Real Estate Less than 60 Months [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans		1,155
Real Estate [Member] | ASC 326 [Member] | Construction Residential Real Estate Less than 60 Months [Member] | Impact of ASC Adoption [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans		(778)
Real Estate [Member] | ASC 326 [Member] | Residential Real Estate First Lien [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans		4,861
Real Estate [Member] | ASC 326 [Member] | Residential Real Estate First Lien [Member] | Impact of ASC Adoption [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans		(3,831)
Real Estate [Member] | ASC 326 [Member] | Residential Real Estate All Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans		1,359
Real Estate [Member] | ASC 326 [Member] | Residential Real Estate All Other [Member] | Impact of ASC Adoption [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans		(1,408)
Real Estate [Member] | ASC 326 [Member] | Farmland [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans		1,413
Real Estate [Member] | ASC 326 [Member] | Farmland [Member] | Impact of ASC Adoption [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans		(1,408)
Commercial and Agricultural Non-Real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans	32,400		13,462
Commercial and Agricultural Non-Real Estate [Member] | Pre ASC 326 Adoption [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans		13,462
Commercial and Agricultural Non-Real Estate [Member] | ASC 326 [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans		26,657
Commercial and Agricultural Non-Real Estate [Member] | ASC 326 [Member] | Impact of ASC Adoption [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans		13,195
Consumer Non-real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans	3,377		3,252
Consumer Non-real Estate [Member] | Pre ASC 326 Adoption [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans		3,252
Consumer Non-real Estate [Member] | ASC 326 [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans		2,630
Consumer Non-real Estate [Member] | ASC 326 [Member] | Impact of ASC Adoption [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans		(622)
Oil and Gas [Member] | Pre ASC 326 Adoption [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans		1,883
Oil and Gas [Member] | ASC 326 [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans		537
Oil and Gas [Member] | ASC 326 [Member] | Impact of ASC Adoption [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans		(1,346)
Other Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans	3,182		2,632	$ 2,423
Other Loans [Member] | Pre ASC 326 Adoption [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans		2,632
Other Loans [Member] | ASC 326 [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans		2,516
Other Loans [Member] | ASC 326 [Member] | Impact of ASC Adoption [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans		(116)
Pegasus Bank [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans	$ 4,556		$ 599
Pegasus Bank [Member] | Pre ASC 326 Adoption [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans		599
Pegasus Bank [Member] | ASC 326 [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans		3,087
Pegasus Bank [Member] | ASC 326 [Member] | Impact of ASC Adoption [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans		$ 2,488