Loans and Allowance for Loan Losses - Internal Loan Grading by Class of Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable Recorded Investment [Line Items]
Total loans	$ 5,042,502	$ 4,975,976
Real Estate [Member] | Non-residential Real Estate Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	639,019	626,621
Real Estate [Member] | Non-residential Real Estate Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,189,769	1,146,128
Real Estate [Member] | Residential Real Estate Permanent Mortgage [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	333,666	328,702
Real Estate [Member] | Residential Real Estate All Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	841,433	827,504
Commercial and Financial [Member] | Non-consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,326,604	1,283,654
Consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	327,006	326,862
Other Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	142,420	141,909
Acquired Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	242,585	294,596
Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	3,959,825	3,902,046
Grade 1 [Member] | Real Estate [Member] | Non-residential Real Estate Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	459,381	451,059
Grade 1 [Member] | Real Estate [Member] | Non-residential Real Estate Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	956,483	932,454
Grade 1 [Member] | Real Estate [Member] | Residential Real Estate Permanent Mortgage [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	283,951	279,870
Grade 1 [Member] | Real Estate [Member] | Residential Real Estate All Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	659,846	644,217
Grade 1 [Member] | Commercial and Financial [Member] | Non-consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,033,690	1,000,089
Grade 1 [Member] | Consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	302,263	302,217
Grade 1 [Member] | Other Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	136,737	136,132
Grade 1 [Member] | Acquired Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	127,474	156,008
Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	945,165	948,216
Grade 2 [Member] | Real Estate [Member] | Non-residential Real Estate Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	153,357	157,715
Grade 2 [Member] | Real Estate [Member] | Non-residential Real Estate Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	206,591	188,341
Grade 2 [Member] | Real Estate [Member] | Residential Real Estate Permanent Mortgage [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	41,010	39,806
Grade 2 [Member] | Real Estate [Member] | Residential Real Estate All Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	159,703	162,003
Grade 2 [Member] | Commercial and Financial [Member] | Non-consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	264,192	264,134
Grade 2 [Member] | Consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	21,860	21,600
Grade 2 [Member] | Other Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	4,317	5,542
Grade 2 [Member] | Acquired Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	94,135	109,075
Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	115,919	103,111
Grade 3 [Member] | Real Estate [Member] | Non-residential Real Estate Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	25,456	16,949
Grade 3 [Member] | Real Estate [Member] | Non-residential Real Estate Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	25,665	25,146
Grade 3 [Member] | Real Estate [Member] | Residential Real Estate Permanent Mortgage [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	7,080	7,401
Grade 3 [Member] | Real Estate [Member] | Residential Real Estate All Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	15,943	15,232
Grade 3 [Member] | Commercial and Financial [Member] | Non-consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	24,726	15,128
Grade 3 [Member] | Consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	2,246	2,255
Grade 3 [Member] | Other Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,348	116
Grade 3 [Member] | Acquired Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	13,455	20,884
Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	21,278	22,258
Grade 4 [Member] | Real Estate [Member] | Non-residential Real Estate Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	825	898
Grade 4 [Member] | Real Estate [Member] | Non-residential Real Estate Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,030	187
Grade 4 [Member] | Real Estate [Member] | Residential Real Estate Permanent Mortgage [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,625	1,625
Grade 4 [Member] | Real Estate [Member] | Residential Real Estate All Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	5,941	6,052
Grade 4 [Member] | Commercial and Financial [Member] | Non-consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	3,996	4,303
Grade 4 [Member] | Consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	637	790
Grade 4 [Member] | Other Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	18	119
Grade 4 [Member] | Acquired Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	7,206	8,284
Grade 5 [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	315	345
Grade 5 [Member] | Acquired Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	$ 315	$ 345