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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

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