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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 |  |

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