Allowance for Loan Losses - Summary of Activity in Allowance for Loan Losses, Net of Unearned Fees for Periods Indicated (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Loans and Leases Receivable Disclosure [Line Items]
Allowance for Loan Losses, Loans pooled for evaluation	$ 30,266	$ 27,352	$ 27,760
Allowance for Loan Losses, Individually evaluated for impairment	2,194	2,699	2,046
Total allowance for loan losses	32,582	30,323	32,503	$ 36,011
Loans, Net of Unearned fees , Loans pooled for evaluation	3,979,744	2,971,371	2,706,409
Loans, Net of Unearned fees , Individually evaluated for impairment	28,047	28,234	28,140
Total loans, net of unamortized deferred loan fees and discounts	4,022,014	3,015,165	2,759,593
Mortgage Loans on Real Estate [Member]
Loans and Leases Receivable Disclosure [Line Items]
Allowance for Loan Losses, Loans pooled for evaluation	15,357	13,283	12,368
Allowance for Loan Losses, Individually evaluated for impairment	147	260	262
Total allowance for loan losses	15,620	13,758	14,265	13,911
Loans, Net of Unearned fees , Loans pooled for evaluation	3,116,086	2,271,165	2,020,018
Loans, Net of Unearned fees , Individually evaluated for impairment	16,884	19,209	19,175
Total loans, net of unamortized deferred loan fees and discounts	3,143,100	2,300,322	2,053,464
Mortgage Loans on Real Estate [Member] | Commercial [Member]
Loans and Leases Receivable Disclosure [Line Items]
Allowance for Loan Losses, Loans pooled for evaluation	12,737	11,351	10,064
Allowance for Loan Losses, Individually evaluated for impairment	91	30	4
Total allowance for loan losses	12,944	11,441	11,517	11,015
Loans, Net of Unearned fees , Loans pooled for evaluation	2,606,819	1,892,422	1,657,238
Loans, Net of Unearned fees , Individually evaluated for impairment	12,563	13,911	15,081
Total loans, net of unamortized deferred loan fees and discounts	2,627,838	1,914,896	1,685,121
Consumer [Member]
Loans and Leases Receivable Disclosure [Line Items]
Allowance for Loan Losses, Loans pooled for evaluation	8,103	7,619	9,575
Allowance for Loan Losses, Individually evaluated for impairment	266	591	654
Total allowance for loan losses	8,375	8,227	10,310	15,118
Loans, Net of Unearned fees , Loans pooled for evaluation	411,389	349,431	355,698
Loans, Net of Unearned fees , Individually evaluated for impairment	5,945	4,415	4,858
Total loans, net of unamortized deferred loan fees and discounts	418,982	356,874	366,663
Consumer [Member] | Home Equity Lines of Credit [Member]
Loans and Leases Receivable Disclosure [Line Items]
Allowance for Loan Losses, Loans pooled for evaluation	5,838	5,356	6,616
Allowance for Loan Losses, Individually evaluated for impairment	198	427	411
Total allowance for loan losses	6,042	5,800	7,044	11,253
Loans, Net of Unearned fees , Loans pooled for evaluation	322,764	283,502	282,159
Loans, Net of Unearned fees , Individually evaluated for impairment	2,646	2,688	3,196
Total loans, net of unamortized deferred loan fees and discounts	326,577	288,688	289,715
Commercial Portfolio Segment [Member]
Loans and Leases Receivable Disclosure [Line Items]
Allowance for Loan Losses, Loans pooled for evaluation	4,309	4,624	3,765
Allowance for Loan Losses, Individually evaluated for impairment	1,781	1,848	1,130
Total allowance for loan losses	6,090	6,512	5,831	5,271
Loans, Net of Unearned fees , Loans pooled for evaluation	268,885	213,358	208,960
Loans, Net of Unearned fees , Individually evaluated for impairment	5,218	4,470	4,096
Total loans, net of unamortized deferred loan fees and discounts	276,548	220,412	217,047
Construction [Member]
Loans and Leases Receivable Disclosure [Line Items]
Allowance for Loan Losses, Loans pooled for evaluation	2,497	1,826	2,052
Total allowance for loan losses	2,497	1,826	2,097	1,711
Loans, Net of Unearned fees , Loans pooled for evaluation	183,384	137,417	121,733
Loans, Net of Unearned fees , Individually evaluated for impairment		140	11
Total loans, net of unamortized deferred loan fees and discounts	183,384	137,557	122,419
Construction [Member] | Commercial [Member]
Loans and Leases Receivable Disclosure [Line Items]
Allowance for Loan Losses, Loans pooled for evaluation	663	642	680
Total allowance for loan losses	663	642	680	812
Loans, Net of Unearned fees , Loans pooled for evaluation	62,088	69,627	66,990
Total loans, net of unamortized deferred loan fees and discounts	62,088	69,627	66,990
Construction [Member] | Residential [Member]
Loans and Leases Receivable Disclosure [Line Items]
Allowance for Loan Losses, Loans pooled for evaluation	1,834	1,184	1,372
Total allowance for loan losses	1,834	1,184	1,417	899
Loans, Net of Unearned fees , Loans pooled for evaluation	121,296	67,790	54,743
Loans, Net of Unearned fees , Individually evaluated for impairment		140	11
Total loans, net of unamortized deferred loan fees and discounts	121,296	67,930	55,429
Residential 1-4 Family [Member] | Mortgage Loans on Real Estate [Member]
Loans and Leases Receivable Disclosure [Line Items]
Allowance for Loan Losses, Loans pooled for evaluation	2,620	1,932	2,304
Allowance for Loan Losses, Individually evaluated for impairment	56	230	258
Total allowance for loan losses	2,676	2,317	2,748	2,896
Loans, Net of Unearned fees , Loans pooled for evaluation	509,267	378,743	362,780
Loans, Net of Unearned fees , Individually evaluated for impairment	4,321	5,298	4,094
Total loans, net of unamortized deferred loan fees and discounts	515,262	385,426	368,343
Home Equity Loans [Member] | Consumer [Member]
Loans and Leases Receivable Disclosure [Line Items]
Allowance for Loan Losses, Loans pooled for evaluation	1,486	1,734	2,365
Allowance for Loan Losses, Individually evaluated for impairment	54	107	215
Total allowance for loan losses	1,540	1,841	2,644	3,177
Loans, Net of Unearned fees , Loans pooled for evaluation	33,142	41,076	42,992
Loans, Net of Unearned fees , Individually evaluated for impairment	3,103	1,470	1,508
Total loans, net of unamortized deferred loan fees and discounts	36,684	43,031	46,182
Other Consumer [Member] | Consumer [Member]
Loans and Leases Receivable Disclosure [Line Items]
Allowance for Loan Losses, Loans pooled for evaluation	779	529	594
Allowance for Loan Losses, Individually evaluated for impairment	14	57	28
Total allowance for loan losses	793	586	622	$ 688
Loans, Net of Unearned fees , Loans pooled for evaluation	55,483	24,853	30,547
Loans, Net of Unearned fees , Individually evaluated for impairment	196	257	154
Total loans, net of unamortized deferred loan fees and discounts	55,721	25,155	30,766
Financial Asset Acquired with Credit Deterioration [Member]
Loans and Leases Receivable Disclosure [Line Items]
Allowance for Loan Losses, Loans acquired with deteriorated credit quality	122	272	2,697
Total loans, net of unamortized deferred loan fees and discounts	14,223	15,560	25,044
Financial Asset Acquired with Credit Deterioration [Member] | Mortgage Loans on Real Estate [Member]
Loans and Leases Receivable Disclosure [Line Items]
Allowance for Loan Losses, Loans acquired with deteriorated credit quality	116	215	1,635
Total loans, net of unamortized deferred loan fees and discounts	10,130	9,948	14,271
Financial Asset Acquired with Credit Deterioration [Member] | Mortgage Loans on Real Estate [Member] | Commercial [Member]
Loans and Leases Receivable Disclosure [Line Items]
Allowance for Loan Losses, Loans acquired with deteriorated credit quality	116	60	1,449
Total loans, net of unamortized deferred loan fees and discounts	8,456	8,563	12,802
Financial Asset Acquired with Credit Deterioration [Member] | Consumer [Member]
Loans and Leases Receivable Disclosure [Line Items]
Allowance for Loan Losses, Loans acquired with deteriorated credit quality	6	17	81
Total loans, net of unamortized deferred loan fees and discounts	1,648	3,028	6,107
Financial Asset Acquired with Credit Deterioration [Member] | Consumer [Member] | Home Equity Lines of Credit [Member]
Loans and Leases Receivable Disclosure [Line Items]
Allowance for Loan Losses, Loans acquired with deteriorated credit quality	6	17	17
Total loans, net of unamortized deferred loan fees and discounts	1,167	2,498	4,360
Financial Asset Acquired with Credit Deterioration [Member] | Commercial Portfolio Segment [Member]
Loans and Leases Receivable Disclosure [Line Items]
Allowance for Loan Losses, Loans acquired with deteriorated credit quality		40	936
Total loans, net of unamortized deferred loan fees and discounts	2,445	2,584	3,991
Financial Asset Acquired with Credit Deterioration [Member] | Construction [Member]
Loans and Leases Receivable Disclosure [Line Items]
Allowance for Loan Losses, Loans acquired with deteriorated credit quality			45
Total loans, net of unamortized deferred loan fees and discounts			675
Financial Asset Acquired with Credit Deterioration [Member] | Construction [Member] | Residential [Member]
Loans and Leases Receivable Disclosure [Line Items]
Allowance for Loan Losses, Loans acquired with deteriorated credit quality			45
Total loans, net of unamortized deferred loan fees and discounts			675
Financial Asset Acquired with Credit Deterioration [Member] | Residential 1-4 Family [Member] | Mortgage Loans on Real Estate [Member]
Loans and Leases Receivable Disclosure [Line Items]
Allowance for Loan Losses, Loans acquired with deteriorated credit quality		155	186
Total loans, net of unamortized deferred loan fees and discounts	1,674	1,385	1,469
Financial Asset Acquired with Credit Deterioration [Member] | Home Equity Loans [Member] | Consumer [Member]
Loans and Leases Receivable Disclosure [Line Items]
Allowance for Loan Losses, Loans acquired with deteriorated credit quality			64
Total loans, net of unamortized deferred loan fees and discounts	439	485	1,682
Financial Asset Acquired with Credit Deterioration [Member] | Other Consumer [Member] | Consumer [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	$ 42	$ 45	$ 65