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	Sep. 30, 2020	Jun. 30, 2020	Jan. 01, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans	$ 106,126	$ 89,500		$ 54,238	$ 55,928	$ 55,108	$ 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	7,894	6,630		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 Owner Occupied [Member] | ASC 326 [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans			2,819
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member] | ASC 326 [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] | Commercial Real Estate Non-Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans	14,904	9,483		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] | Commercial Real Estate Non-Owner Occupied [Member] | ASC 326 [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans			2,851
Real Estate [Member] | Commercial Real Estate Non-Owner Occupied [Member] | ASC 326 [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] | Construction and Development Less than 60 Months [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans	1,589	1,755		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 and Development Less than 60 Months [Member] | ASC 326 [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans			1,158
Real Estate [Member] | Construction and Development Less than 60 Months [Member] | ASC 326 [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] | Construction Residential Real Estate Less than 60 Months [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans	2,660	2,259		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] | Construction Residential Real Estate Less than 60 Months [Member] | ASC 326 [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans			1,155
Real Estate [Member] | Construction Residential Real Estate Less than 60 Months [Member] | ASC 326 [Member] | Impact of ASC Adoption [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans			(778)
Real Estate [Member] | Residential Real Estate First Lien [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans	10,264	8,553		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 First Lien [Member] | ASC 326 [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans			4,861
Real Estate [Member] | Residential Real Estate First Lien [Member] | ASC 326 [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] | Residential Real Estate All Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans	2,856	2,720		2,767	12,201	11,721	10,673
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] | Residential Real Estate All Other [Member] | ASC 326 [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans			1,359
Real Estate [Member] | Residential Real Estate All Other [Member] | ASC 326 [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] | 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] | Farmland [Member] | ASC 326 [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans			1,413
Real Estate [Member] | Farmland [Member] | ASC 326 [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	49,442	44,505		15,345
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			15,345
Commercial and Agricultural Non-Real Estate [Member] | ASC 326 [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans			27,194
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			11,849
Consumer Non-real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans	5,101	4,714		3,252	3,274	3,234	3,065
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)
Other Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses on loans	3,221	2,513		2,632	2,647	$ 2,449	$ 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	$ 3,785	$ 3,857		$ 599	$ 64
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