Non-performing Loans and Impaired Loans - Payment Status by Class of Loan (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	$ 3,599,697	$ 2,996,548
Total Past Due	16,662	12,605
Loans Not Past Due	24,464	20,334
Total	$ 3,624,161	$ 3,016,771
Total Past Due, Percentage of Total Loans	0.46%	0.42%
Loans Not Past Due, Percentage of Total Loans	0.68%	0.67%
Current,Percentage of total loans	99.32%	99.33%
Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	$ 2,078,416	$ 1,715,104
Total Past Due	9,297	6,586
Loans Not Past Due	14,828	10,265
Total	2,093,244	1,725,369
Commercial [Member] | Owner Occupied Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	672,729	556,516
Total Past Due	3,761	3,413
Loans Not Past Due	3,788	4,947
Total	676,517	561,463
Commercial [Member] | Non Owner Occupied Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	827,610	716,574
Total Past Due	3,445	1,046
Loans Not Past Due	6,193	1,240
Total	833,803	717,814
Commercial [Member] | Residential Spec Homes [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	9,469	4,707
Total Past Due	261
Loans Not Past Due	752	492
Total	10,221	5,199
Commercial [Member] | Development & Spec Land [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	74,885	46,479
Total Past Due	177	68
Loans Not Past Due	194	68
Total	75,079	46,547
Commercial [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	493,723	390,828
Total Past Due	1,653	2,059
Loans Not Past Due	3,901	3,518
Total	497,624	394,346
Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	887,385	739,650
Total Past Due	4,107	3,269
Loans Not Past Due	6,326	4,636
Total	893,711	744,286
Real Estate [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	790,848	641,500
Total Past Due	4,107	3,269
Loans Not Past Due	6,326	4,636
Total	797,174	646,136
Real Estate [Member] | Residential Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	24,593	24,030
Total	24,593	24,030
Real Estate [Member] | Mortgage Warehousing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	71,944	74,120
Total	71,944	74,120
Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	633,896	541,794
Total Past Due	3,258	2,750
Loans Not Past Due	3,310	5,433
Total	637,206	547,116
Consumer [Member] | Direct Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	37,345	38,027
Total Past Due	55	35
Loans Not Past Due	72	146
Total	37,417	38,173
Consumer [Member] | Indirect Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	316,613	311,494
Total Past Due	986	916
Loans Not Past Due	1,016	2,683
Total	317,629	314,177
Consumer [Member] | Home Equity Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	279,938	192,162
Total Past Due	2,217	1,799
Loans Not Past Due	2,222	2,604
Total	282,160	194,766
30 - 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 8,376	$ 5,100
Total Past Due, Percentage of Total Loans	0.23%	0.17%
30 - 59 Days Past Due [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 4,537	$ 1,719
30 - 59 Days Past Due [Member] | Commercial [Member] | Owner Occupied Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	27	537
30 - 59 Days Past Due [Member] | Commercial [Member] | Non Owner Occupied Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,386	175
30 - 59 Days Past Due [Member] | Commercial [Member] | Residential Spec Homes [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	491	492
30 - 59 Days Past Due [Member] | Commercial [Member] | Development & Spec Land [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	17
30 - 59 Days Past Due [Member] | Commercial [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,616	515
30 - 59 Days Past Due [Member] | Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,910	1,131
30 - 59 Days Past Due [Member] | Real Estate [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,910	1,131
30 - 59 Days Past Due [Member] | Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,929	2,250
30 - 59 Days Past Due [Member] | Consumer [Member] | Direct Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	67	93
30 - 59 Days Past Due [Member] | Consumer [Member] | Indirect Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	906	1,396
30 - 59 Days Past Due [Member] | Consumer [Member] | Home Equity Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	956	761
60 - 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 1,604	$ 2,061
Total Past Due, Percentage of Total Loans	0.04%	0.07%
60 - 89 Days Past Due [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 994	$ 1,752
60 - 89 Days Past Due [Member] | Commercial [Member] | Owner Occupied Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		997
60 - 89 Days Past Due [Member] | Commercial [Member] | Non Owner Occupied Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	362	19
60 - 89 Days Past Due [Member] | Commercial [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	632	736
60 - 89 Days Past Due [Member] | Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	169	56
60 - 89 Days Past Due [Member] | Real Estate [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	169	56
60 - 89 Days Past Due [Member] | Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	441	253
60 - 89 Days Past Due [Member] | Consumer [Member] | Direct Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	48	18
60 - 89 Days Past Due [Member] | Consumer [Member] | Indirect Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	129	198
60 - 89 Days Past Due [Member] | Consumer [Member] | Home Equity Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	264	37
Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 192	$ 568
Total Past Due, Percentage of Total Loans	0.01%	0.02%
Greater than 90 Days Past Due [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		$ 208
Greater than 90 Days Past Due [Member] | Commercial [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		208
Greater than 90 Days Past Due [Member] | Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 140	180
Greater than 90 Days Past Due [Member] | Real Estate [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	140	180
Greater than 90 Days Past Due [Member] | Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	52	180
Greater than 90 Days Past Due [Member] | Consumer [Member] | Direct Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	17
Greater than 90 Days Past Due [Member] | Consumer [Member] | Indirect Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	30	173
Greater than 90 Days Past Due [Member] | Consumer [Member] | Home Equity Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 5	$ 7