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Loans and Allowance for Loan Losses - Internal Loan Grading by Class of Loans (Detail) - USD ($) $ in Thousands | Dec. 31, 2018 | Dec. 31, 2017
--- | --- | ---
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | $ 4,975,976 | $ 4,721,995
Real Estate [Member] | Non-residential Real Estate Owner Occupied [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 626,621 | 641,618
Real Estate [Member] | Non-residential Real Estate Other [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 1,146,128 | 1,126,591
Real Estate [Member] | Residential Real Estate Permanent Mortgage [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 328,702 | 330,334
Real Estate [Member] | Residential Real Estate All Other [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 827,504 | 785,655
Commercial and Financial [Member] | Non-consumer Non-real Estate [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 1,283,654 | 1,284,405
Consumer Non-real Estate [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 326,862 | 288,920
Other Loans [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 141,909 | 144,445
Acquired Loans [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 294,596 | 120,027
Grade 1 [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 3,902,046 | 3,851,837
Grade 1 [Member] | Real Estate [Member] | Non-residential Real Estate Owner Occupied [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 451,059 | 520,641
Grade 1 [Member] | Real Estate [Member] | Non-residential Real Estate Other [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 932,454 | 931,295
Grade 1 [Member] | Real Estate [Member] | Residential Real Estate Permanent Mortgage [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 279,870 | 289,200
Grade 1 [Member] | Real Estate [Member] | Residential Real Estate All Other [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 644,217 | 621,401
Grade 1 [Member] | Commercial and Financial [Member] | Non-consumer Non-real Estate [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 1,000,089 | 1,018,172
Grade 1 [Member] | Consumer Non-real Estate [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 302,217 | 268,826
Grade 1 [Member] | Other Loans [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 136,132 | 136,617
Grade 1 [Member] | Acquired Loans [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 156,008 | 65,685
Grade 2 [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 948,216 | 758,681
Grade 2 [Member] | Real Estate [Member] | Non-residential Real Estate Owner Occupied [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 157,715 | 105,696
Grade 2 [Member] | Real Estate [Member] | Non-residential Real Estate Other [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 188,341 | 178,282
Grade 2 [Member] | Real Estate [Member] | Residential Real Estate Permanent Mortgage [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 39,806 | 33,033
Grade 2 [Member] | Real Estate [Member] | Residential Real Estate All Other [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 162,003 | 149,201
Grade 2 [Member] | Commercial and Financial [Member] | Non-consumer Non-real Estate [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 264,134 | 234,884
Grade 2 [Member] | Consumer Non-real Estate [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 21,600 | 17,499
Grade 2 [Member] | Other Loans [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 5,542 | 5,668
Grade 2 [Member] | Acquired Loans [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 109,075 | 34,418
Grade 3 [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 103,111 | 88,588
Grade 3 [Member] | Real Estate [Member] | Non-residential Real Estate Owner Occupied [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 16,949 | 13,852
Grade 3 [Member] | Real Estate [Member] | Non-residential Real Estate Other [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 25,146 | 14,290
Grade 3 [Member] | Real Estate [Member] | Residential Real Estate Permanent Mortgage [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 7,401 | 6,352
Grade 3 [Member] | Real Estate [Member] | Residential Real Estate All Other [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 15,232 | 9,418
Grade 3 [Member] | Commercial and Financial [Member] | Non-consumer Non-real Estate [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 15,128 | 24,322
Grade 3 [Member] | Consumer Non-real Estate [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 2,255 | 2,038
Grade 3 [Member] | Other Loans [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 116 | 1,203
Grade 3 [Member] | Acquired Loans [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 20,884 | 17,113
Grade 4 [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 22,258 | 22,859
Grade 4 [Member] | Real Estate [Member] | Non-residential Real Estate Owner Occupied [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 898 | 1,429
Grade 4 [Member] | Real Estate [Member] | Non-residential Real Estate Other [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 187 | 2,724
Grade 4 [Member] | Real Estate [Member] | Residential Real Estate Permanent Mortgage [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 1,625 | 1,749
Grade 4 [Member] | Real Estate [Member] | Residential Real Estate All Other [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 6,052 | 5,635
Grade 4 [Member] | Commercial and Financial [Member] | Non-consumer Non-real Estate [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 4,303 | 6,997
Grade 4 [Member] | Consumer Non-real Estate [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 790 | 557
Grade 4 [Member] | Other Loans [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 119 | 957
Grade 4 [Member] | Acquired Loans [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 8,284 | 2,811
Grade 5 [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | 345 | 30
Grade 5 [Member] | Commercial and Financial [Member] | Non-consumer Non-real Estate [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans |  | $ 30
Grade 5 [Member] | Acquired Loans [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Total loans | $ 345 |

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