Non-performing Loans and Impaired Loans - Payment Status by Class of Loan (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 9,650	$ 9,496
Loans Not Past Due	2,841,709	2,816,206
Total	$ 2,851,359	$ 2,825,702
Total Past Due, Percentage of Total Loans	0.34%	0.34%
Loans Not Past Due, Percentage of Total Loans	99.66%	99.66%
Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 7,627	$ 4,749
Loans Not Past Due	1,643,728	1,659,318
Total	1,651,355	1,664,067
Commercial [Member] | Owner Occupied Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	5,536	3,563
Loans Not Past Due	576,160	568,419
Total	581,696	571,982
Commercial [Member] | Non Owner Occupied Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,048	634
Loans Not Past Due	676,884	678,311
Total	677,932	678,945
Commercial [Member] | Residential Spec Homes [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Not Past Due	17,473	16,431
Total	17,473	16,431
Commercial [Member] | Development & Spec Land [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	12	31
Loans Not Past Due	33,724	48,807
Total	33,736	48,838
Commercial [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,031	521
Loans Not Past Due	339,487	347,350
Total	340,518	347,871
Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	681	1,360
Loans Not Past Due	716,489	697,533
Total	717,170	698,893
Real Estate [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	681	1,297
Loans Not Past Due	594,743	587,061
Total	595,424	588,358
Real Estate [Member] | Residential Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		63
Loans Not Past Due	20,447	15,964
Total	20,447	16,027
Real Estate [Member] | Mortgage Warehousing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Not Past Due	101,299	94,508
Total	101,299	94,508
Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,342	3,387
Loans Not Past Due	481,492	459,355
Total	482,834	462,742
Consumer [Member] | Direct Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	7	88
Loans Not Past Due	37,407	37,753
Total	37,414	37,841
Consumer [Member] | Indirect Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	978	2,270
Loans Not Past Due	249,947	225,053
Total	250,925	227,323
Consumer [Member] | Home Equity Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	357	1,029
Loans Not Past Due	194,138	196,549
Total	194,495	197,578
30 - 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 8,932	$ 6,426
Total Past Due, Percentage of Total Loans	0.31%	0.23%
30 - 59 Days Past Due [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 7,323	$ 2,676
30 - 59 Days Past Due [Member] | Commercial [Member] | Owner Occupied Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	5,341	1,613
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	1,048	512
30 - 59 Days Past Due [Member] | Commercial [Member] | Development & Spec Land [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	12	31
30 - 59 Days Past Due [Member] | Commercial [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	922	520
30 - 59 Days Past Due [Member] | Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	602	1,311
30 - 59 Days Past Due [Member] | Real Estate [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	602	1,248
30 - 59 Days Past Due [Member] | Real Estate [Member] | Residential Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		63
30 - 59 Days Past Due [Member] | Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,007	2,439
30 - 59 Days Past Due [Member] | Consumer [Member] | Direct Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	7	78
30 - 59 Days Past Due [Member] | Consumer [Member] | Indirect Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	747	1,859
30 - 59 Days Past Due [Member] | Consumer [Member] | Home Equity Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	253	502
60 - 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 688	$ 2,903
Total Past Due, Percentage of Total Loans	0.02%	0.10%
60 - 89 Days Past Due [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 304	$ 2,073
60 - 89 Days Past Due [Member] | Commercial [Member] | Owner Occupied Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	195	1,950
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		122
60 - 89 Days Past Due [Member] | Commercial [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	109	1
60 - 89 Days Past Due [Member] | Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	79	49
60 - 89 Days Past Due [Member] | Real Estate [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	79	49
60 - 89 Days Past Due [Member] | Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	305	781
60 - 89 Days Past Due [Member] | Consumer [Member] | Direct Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		10
60 - 89 Days Past Due [Member] | Consumer [Member] | Indirect Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	201	244
60 - 89 Days Past Due [Member] | Consumer [Member] | Home Equity Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	104	527
Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 30	$ 167
Total Past Due, Percentage of Total Loans	0.00%	0.01%
Greater than 90 Days Past Due [Member] | Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 30	$ 167
Greater than 90 Days Past Due [Member] | Consumer [Member] | Indirect Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 30	$ 167