Non-performing Loans and Impaired Loans - Loans by Credit Grades (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Total	$ 2,421,076	$ 2,130,369
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	1,270,160	1,066,199
Commercial [Member] | Owner Occupied Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	403,184	337,548
Commercial [Member] | Non Owner Occupied Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	531,560	461,897
Commercial [Member] | Residential Development [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	4,031	5,006
Commercial [Member] | Development & Spec Land Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	43,299	31,228
Commercial [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	288,086	230,520
Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	663,759	664,571
Real Estate [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	553,451	508,233
Real Estate [Member] | Residential Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	14,825	20,611
Real Estate [Member] | Mortgage Warehousing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	95,483	135,727
Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	487,157	399,599
Consumer [Member] | Direct Installment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	85,726	71,150
Consumer [Member] | Direct Installment Purchased [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	88	119
Consumer [Member] | Indirect Installment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	207,293	153,204
Consumer [Member] | Home Equity Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	194,050	175,126
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	$ 2,372,439	$ 2,090,978
Percentage of total loans	97.99%	98.15%
Pass [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	$ 1,230,406	$ 1,035,059
Pass [Member] | Commercial [Member] | Owner Occupied Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	386,856	322,924
Pass [Member] | Commercial [Member] | Non Owner Occupied Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	523,831	455,648
Pass [Member] | Commercial [Member] | Residential Development [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	4,031	5,006
Pass [Member] | Commercial [Member] | Development & Spec Land Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	43,066	31,057
Pass [Member] | Commercial [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	272,622	220,424
Pass [Member] | Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	658,333	659,549
Pass [Member] | Real Estate [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	548,249	503,444
Pass [Member] | Real Estate [Member] | Residential Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	14,601	20,378
Pass [Member] | Real Estate [Member] | Mortgage Warehousing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	95,483	135,727
Pass [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	483,701	396,370
Pass [Member] | Consumer [Member] | Direct Installment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	85,416	70,638
Pass [Member] | Consumer [Member] | Direct Installment Purchased [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	88	119
Pass [Member] | Consumer [Member] | Indirect Installment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	206,259	152,496
Pass [Member] | Consumer [Member] | Home Equity Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	191,938	173,117
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	$ 11,753	$ 9,029
Percentage of total loans	0.49%	0.42%
Special Mention [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	$ 11,753	$ 9,029
Special Mention [Member] | Commercial [Member] | Owner Occupied Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	5,776	4,960
Special Mention [Member] | Commercial [Member] | Non Owner Occupied Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	1,008	341
Special Mention [Member] | Commercial [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	4,969	3,728
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	$ 36,883	$ 30,362
Percentage of total loans	1.52%	1.43%
Substandard [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	$ 28,001	$ 22,111
Substandard [Member] | Commercial [Member] | Owner Occupied Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	10,552	9,664
Substandard [Member] | Commercial [Member] | Non Owner Occupied Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	6,721	5,908
Substandard [Member] | Commercial [Member] | Development & Spec Land Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	233	171
Substandard [Member] | Commercial [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	10,495	6,368
Substandard [Member] | Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	5,426	5,022
Substandard [Member] | Real Estate [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	5,202	4,789
Substandard [Member] | Real Estate [Member] | Residential Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	224	233
Substandard [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	3,456	3,229
Substandard [Member] | Consumer [Member] | Direct Installment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	310	512
Substandard [Member] | Consumer [Member] | Indirect Installment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	1,034	708
Substandard [Member] | Consumer [Member] | Home Equity Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	$ 2,112	$ 2,009
Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Percentage of total loans	0.00%	0.00%