Loans Held for Investment and Allowance for Credit Losses on Loans - Internal Loan Grading by Class of Loans (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Financing Receivable Recorded Investment [Line Items]
Total loans	$ 6,394,506	$ 5,662,143
Real Estate [Member] | Non-residential Real Estate Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		707,416
Real Estate [Member] | Non-residential Real Estate Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		1,137,175
Real Estate [Member] | Residential Real Estate Permanent Mortgage [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		340,572
Real Estate [Member] | Residential Real Estate Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		920,832
Commercial and Financial [Member] | Non-consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		1,454,393
Consumer Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		362,354
Other Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	822,078	154,015
Acquired Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		154,681
Pegasus Bank [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	554,548	430,705
Pegasus Bank [Member] | Real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	272,000
Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		4,462,594
Grade 1 [Member] | Real Estate [Member] | Non-residential Real Estate Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		554,942
Grade 1 [Member] | Real Estate [Member] | Non-residential Real Estate Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		861,108
Grade 1 [Member] | Real Estate [Member] | Residential Real Estate Permanent Mortgage [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		289,350
Grade 1 [Member] | Real Estate [Member] | Residential Real Estate Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		722,983
Grade 1 [Member] | Commercial and Financial [Member] | Non-consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		1,166,155
Grade 1 [Member] | Consumer Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		335,916
Grade 1 [Member] | Other Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	813,858	148,692
Grade 1 [Member] | Acquired Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		88,205
Grade 1 [Member] | Pegasus Bank [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	384,241	295,243
Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		1,081,074
Grade 2 [Member] | Real Estate [Member] | Non-residential Real Estate Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		130,783
Grade 2 [Member] | Real Estate [Member] | Non-residential Real Estate Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		252,134
Grade 2 [Member] | Real Estate [Member] | Residential Real Estate Permanent Mortgage [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		41,754
Grade 2 [Member] | Real Estate [Member] | Residential Real Estate Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		179,951
Grade 2 [Member] | Commercial and Financial [Member] | Non-consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		261,003
Grade 2 [Member] | Consumer Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		23,407
Grade 2 [Member] | Other Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	6,950	3,631
Grade 2 [Member] | Acquired Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		55,087
Grade 2 [Member] | Pegasus Bank [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	168,854	133,324
Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		96,850
Grade 3 [Member] | Real Estate [Member] | Non-residential Real Estate Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		15,191
Grade 3 [Member] | Real Estate [Member] | Non-residential Real Estate Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		23,048
Grade 3 [Member] | Real Estate [Member] | Residential Real Estate Permanent Mortgage [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		6,975
Grade 3 [Member] | Real Estate [Member] | Residential Real Estate Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		14,382
Grade 3 [Member] | Commercial and Financial [Member] | Non-consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		25,276
Grade 3 [Member] | Consumer Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		2,327
Grade 3 [Member] | Other Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	234	1,564
Grade 3 [Member] | Acquired Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		6,800
Grade 3 [Member] | Pegasus Bank [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,453	1,287
Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		21,344
Grade 4 [Member] | Real Estate [Member] | Non-residential Real Estate Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		6,500
Grade 4 [Member] | Real Estate [Member] | Non-residential Real Estate Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		868
Grade 4 [Member] | Real Estate [Member] | Residential Real Estate Permanent Mortgage [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		2,442
Grade 4 [Member] | Real Estate [Member] | Residential Real Estate Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		3,446
Grade 4 [Member] | Commercial and Financial [Member] | Non-consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		1,959
Grade 4 [Member] | Consumer Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		704
Grade 4 [Member] | Other Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	$ 1,036	128
Grade 4 [Member] | Acquired Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		4,446
Grade 4 [Member] | Pegasus Bank [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		851
Grade 5 [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		281
Grade 5 [Member] | Real Estate [Member] | Non-residential Real Estate Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		17
Grade 5 [Member] | Real Estate [Member] | Residential Real Estate Permanent Mortgage [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		51
Grade 5 [Member] | Real Estate [Member] | Residential Real Estate Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		70
Grade 5 [Member] | Acquired Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		$ 143