Non-performing Loans and Impaired Loans - Loans by Credit Grades (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment [Line Items]
Total	$ 3,673,814	$ 3,016,771
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	2,067,533	1,725,369
Commercial [Member] | Owner Occupied Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	709,597	561,463
Commercial [Member] | Non Owner Occupied Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	783,092	717,814
Commercial [Member] | Residential Development [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	14,862	5,199
Commercial [Member] | Development & Spec Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	41,102	46,547
Commercial [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	518,880	394,346
Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	954,644	744,286
Real Estate [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	798,813	646,136
Real Estate [Member] | Residential Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	22,403	24,030
Real Estate [Member] | Mortgage Warehousing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	133,428	74,120
Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	651,637	547,116
Consumer [Member] | Direct Installment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	46,468	38,173
Consumer [Member] | Indirect Installment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	329,773	314,177
Consumer [Member] | Home Equity Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	275,396	194,766
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	$ 3,582,026	$ 2,954,944
Percentage of total loans	97.50%	97.95%
Pass [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	$ 1,985,899	$ 1,671,634
Pass [Member] | Commercial [Member] | Owner Occupied Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	686,630	538,177
Pass [Member] | Commercial [Member] | Non Owner Occupied Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	764,517	702,269
Pass [Member] | Commercial [Member] | Residential Development [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	14,862	5,199
Pass [Member] | Commercial [Member] | Development & Spec Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	37,847	46,382
Pass [Member] | Commercial [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	482,043	379,607
Pass [Member] | Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	948,277	739,459
Pass [Member] | Real Estate [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	792,446	641,309
Pass [Member] | Real Estate [Member] | Residential Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	22,403	24,030
Pass [Member] | Real Estate [Member] | Mortgage Warehousing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	133,428	74,120
Pass [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	647,850	543,851
Pass [Member] | Consumer [Member] | Direct Installment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	46,433	38,138
Pass [Member] | Consumer [Member] | Indirect Installment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	328,488	313,088
Pass [Member] | Consumer [Member] | Home Equity Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	272,929	192,625
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	$ 44,024	$ 23,052
Percentage of total loans	1.20%	0.76%
Special Mention [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	$ 44,024	$ 23,052
Special Mention [Member] | Commercial [Member] | Owner Occupied Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	5,711	6,618
Special Mention [Member] | Commercial [Member] | Non Owner Occupied Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	13,002	9,682
Special Mention [Member] | Commercial [Member] | Development & Spec Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	97	97
Special Mention [Member] | Commercial [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	25,214	6,655
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	$ 47,764	$ 38,775
Percentage of total loans	1.30%	1.29%
Substandard [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	$ 37,610	$ 30,683
Substandard [Member] | Commercial [Member] | Owner Occupied Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	17,256	16,668
Substandard [Member] | Commercial [Member] | Non Owner Occupied Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	5,573	5,863
Substandard [Member] | Commercial [Member] | Development & Spec Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	3,158	68
Substandard [Member] | Commercial [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	11,623	8,084
Substandard [Member] | Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	6,367	4,827
Substandard [Member] | Real Estate [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	6,367	4,827
Substandard [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	3,787	3,265
Substandard [Member] | Consumer [Member] | Direct Installment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	35	35
Substandard [Member] | Consumer [Member] | Indirect Installment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	1,285	1,089
Substandard [Member] | Consumer [Member] | Home Equity Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	$ 2,467	$ 2,141
Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Percentage of total loans	0.00%	0.00%