Non-performing Loans and Impaired Loans - Loans by Credit Grades (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment [Line Items]
Total	$ 3,624,161	$ 3,016,771
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	2,093,244	1,725,369
Commercial [Member] | Owner Occupied Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	676,517	561,463
Commercial [Member] | Non Owner Occupied Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	833,803	717,814
Commercial [Member] | Residential Development [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	10,221	5,199
Commercial [Member] | Development & Spec Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	75,079	46,547
Commercial [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	497,624	394,346
Commercial [Member] | Residential Spec Homes [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	10,221	5,199
Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	893,711	744,286
Real Estate [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	797,174	646,136
Real Estate [Member] | Residential Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	24,593	24,030
Real Estate [Member] | Mortgage Warehousing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	71,944	74,120
Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	637,206	547,116
Consumer [Member] | Direct Installment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	37,417	38,173
Consumer [Member] | Indirect Installment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	317,629	314,177
Consumer [Member] | Home Equity Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	282,160	194,766
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	$ 3,561,168	$ 2,954,944
Percentage of total loans	98.26%	97.95%
Pass [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	$ 2,039,184	$ 1,671,634
Pass [Member] | Commercial [Member] | Owner Occupied Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	656,354	538,177
Pass [Member] | Commercial [Member] | Non Owner Occupied Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	815,974	702,269
Pass [Member] | Commercial [Member] | Residential Development [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	9,960	5,199
Pass [Member] | Commercial [Member] | Development & Spec Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	74,805	46,382
Pass [Member] | Commercial [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	482,091	379,607
Pass [Member] | Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	888,200	739,459
Pass [Member] | Real Estate [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	791,663	641,309
Pass [Member] | Real Estate [Member] | Residential Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	24,593	24,030
Pass [Member] | Real Estate [Member] | Mortgage Warehousing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	71,944	74,120
Pass [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	633,784	543,851
Pass [Member] | Consumer [Member] | Direct Installment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	37,345	38,138
Pass [Member] | Consumer [Member] | Indirect Installment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	316,613	313,088
Pass [Member] | Consumer [Member] | Home Equity Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	279,826	192,625
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	$ 21,265	$ 23,052
Percentage of total loans	0.59%	0.76%
Special Mention [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	$ 21,265	$ 23,052
Special Mention [Member] | Commercial [Member] | Owner Occupied Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	5,046	6,618
Special Mention [Member] | Commercial [Member] | Non Owner Occupied Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	9,048	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	7,074	6,655
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	$ 41,728	$ 38,775
Percentage of total loans	1.15%	1.29%
Substandard [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	$ 32,795	$ 30,683
Substandard [Member] | Commercial [Member] | Owner Occupied Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	15,117	16,668
Substandard [Member] | Commercial [Member] | Non Owner Occupied Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	8,781	5,863
Substandard [Member] | Commercial [Member] | Development & Spec Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	177	68
Substandard [Member] | Commercial [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	8,459	8,084
Substandard [Member] | Commercial [Member] | Residential Spec Homes [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	261
Substandard [Member] | Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	5,511	4,827
Substandard [Member] | Real Estate [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	5,511	4,827
Substandard [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	3,422	3,265
Substandard [Member] | Consumer [Member] | Direct Installment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	72	35
Substandard [Member] | Consumer [Member] | Indirect Installment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	1,016	1,089
Substandard [Member] | Consumer [Member] | Home Equity Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	$ 2,334	$ 2,141
Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Percentage of total loans	0.00%	0.00%