Allowance for Loan Losses - Summary of Activity in Allowance for Loan Losses, Net of Unearned Fees for Periods Indicated (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Loans and Leases Receivable Disclosure [Line Items]
Allowance for Loan Losses, Loans pooled for evaluation	$ 30,416		$ 30,266	$ 26,496
Allowance for Loan Losses, Individually evaluated for impairment	2,442		2,194	2,889
Total allowance for loan losses	32,868	$ 32,064	32,582	29,524	$ 29,973	$ 30,323
Loans, Net of Unearned fees , Loans pooled for evaluation	4,067,497		3,979,744	3,105,241
Loans, Net of Unearned fees , Individually evaluated for impairment	24,695		28,047	27,211
Total loans, net of unamortized deferred loan fees and discounts	4,103,687		4,022,014	3,146,313
Mortgage Loans on Real Estate [Member]
Loans and Leases Receivable Disclosure [Line Items]
Allowance for Loan Losses, Loans pooled for evaluation	14,537		15,357	13,260
Allowance for Loan Losses, Individually evaluated for impairment	138		147	229
Total allowance for loan losses	14,675	14,830	15,620	13,598	13,665	13,758
Loans, Net of Unearned fees , Loans pooled for evaluation	3,155,996		3,116,086	2,374,219
Loans, Net of Unearned fees , Individually evaluated for impairment	15,335		16,884	17,506
Total loans, net of unamortized deferred loan fees and discounts	3,178,730		3,143,100	2,401,040
Mortgage Loans on Real Estate [Member] | Commercial [Member]
Loans and Leases Receivable Disclosure [Line Items]
Allowance for Loan Losses, Loans pooled for evaluation	12,015		12,737	11,466
Allowance for Loan Losses, Individually evaluated for impairment	84		91	82
Total allowance for loan losses	12,099	12,330	12,944	11,607	11,495	11,441
Loans, Net of Unearned fees , Loans pooled for evaluation	2,655,692		2,606,819	1,997,591
Loans, Net of Unearned fees , Individually evaluated for impairment	11,030		12,563	11,162
Total loans, net of unamortized deferred loan fees and discounts	2,672,681		2,627,838	2,016,348
Consumer [Member]
Loans and Leases Receivable Disclosure [Line Items]
Allowance for Loan Losses, Loans pooled for evaluation	8,378		8,103	6,597
Allowance for Loan Losses, Individually evaluated for impairment	164		266	533
Total allowance for loan losses	8,552	8,341	8,375	7,137	7,718	8,227
Loans, Net of Unearned fees , Loans pooled for evaluation	428,572		411,389	343,898
Loans, Net of Unearned fees , Individually evaluated for impairment	4,258		5,945	4,954
Total loans, net of unamortized deferred loan fees and discounts	434,388		418,982	350,925
Consumer [Member] | Home Equity Lines of Credit [Member]
Loans and Leases Receivable Disclosure [Line Items]
Allowance for Loan Losses, Loans pooled for evaluation	5,764		5,838	4,754
Allowance for Loan Losses, Individually evaluated for impairment	85		198	287
Total allowance for loan losses	5,859	6,015	6,042	5,048	5,412	5,800
Loans, Net of Unearned fees , Loans pooled for evaluation	327,726		322,764	282,611
Loans, Net of Unearned fees , Individually evaluated for impairment	2,046		2,646	2,250
Total loans, net of unamortized deferred loan fees and discounts	330,900		326,577	286,436
Commercial Portfolio Segment [Member]
Loans and Leases Receivable Disclosure [Line Items]
Allowance for Loan Losses, Loans pooled for evaluation	4,605		4,309	4,228
Allowance for Loan Losses, Individually evaluated for impairment	2,140		1,781	2,127
Total allowance for loan losses	6,745	6,078	6,090	6,378	6,392	6,512
Loans, Net of Unearned fees , Loans pooled for evaluation	268,405		268,885	230,395
Loans, Net of Unearned fees , Individually evaluated for impairment	5,102		5,218	4,751
Total loans, net of unamortized deferred loan fees and discounts	276,045		276,548	237,619
Construction [Member]
Loans and Leases Receivable Disclosure [Line Items]
Allowance for Loan Losses, Loans pooled for evaluation	2,896		2,497	2,411
Total allowance for loan losses	2,896	2,815	2,497	2,411	2,198	1,826
Loans, Net of Unearned fees , Loans pooled for evaluation	214,524		183,384	156,729
Loans, Net of Unearned fees , Individually evaluated for impairment				0
Total loans, net of unamortized deferred loan fees and discounts	214,524		183,384	156,729
Construction [Member] | Commercial [Member]
Loans and Leases Receivable Disclosure [Line Items]
Allowance for Loan Losses, Loans pooled for evaluation	358		663	977
Total allowance for loan losses	358	407	663	977	847	642
Loans, Net of Unearned fees , Loans pooled for evaluation	57,009		62,088	83,151
Total loans, net of unamortized deferred loan fees and discounts	57,009		62,088	83,151
Construction [Member] | Residential [Member]
Loans and Leases Receivable Disclosure [Line Items]
Allowance for Loan Losses, Loans pooled for evaluation	2,538		1,834	1,434
Total allowance for loan losses	2,538	2,408	1,834	1,434	1,351	1,184
Loans, Net of Unearned fees , Loans pooled for evaluation	157,515		121,296	73,578
Total loans, net of unamortized deferred loan fees and discounts	157,515		121,296	73,578
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	2,522		2,620	1,794
Allowance for Loan Losses, Individually evaluated for impairment	54		56	147
Total allowance for loan losses	2,576	2,500	2,676	1,991	2,170	2,317
Loans, Net of Unearned fees , Loans pooled for evaluation	500,304		509,267	376,628
Loans, Net of Unearned fees , Individually evaluated for impairment	4,305		4,321	6,344
Total loans, net of unamortized deferred loan fees and discounts	506,049		515,262	384,692
Home Equity Loans [Member] | Consumer [Member]
Loans and Leases Receivable Disclosure [Line Items]
Allowance for Loan Losses, Loans pooled for evaluation	1,181		1,486	1,340
Allowance for Loan Losses, Individually evaluated for impairment	61		54	192
Total allowance for loan losses	1,242	1,286	1,540	1,532	1,736	1,841
Loans, Net of Unearned fees , Loans pooled for evaluation	29,860		33,142	38,074
Loans, Net of Unearned fees , Individually evaluated for impairment	2,056		3,103	2,457
Total loans, net of unamortized deferred loan fees and discounts	32,345		36,684	40,986
Other Consumer [Member] | Consumer [Member]
Loans and Leases Receivable Disclosure [Line Items]
Allowance for Loan Losses, Loans pooled for evaluation	1,433		779	503
Allowance for Loan Losses, Individually evaluated for impairment	18		14	54
Total allowance for loan losses	1,451	$ 1,040	793	557	$ 570	$ 586
Loans, Net of Unearned fees , Loans pooled for evaluation	70,986		55,483	23,213
Loans, Net of Unearned fees , Individually evaluated for impairment	156		196	247
Total loans, net of unamortized deferred loan fees and discounts	71,143		55,721	23,503
Financial Asset Acquired with Credit Deterioration [Member]
Loans and Leases Receivable Disclosure [Line Items]
Allowance for Loan Losses, Loans acquired with deteriorated credit quality	10		122	139
Total loans, net of unamortized deferred loan fees and discounts	11,495		14,223	13,861
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	109
Total loans, net of unamortized deferred loan fees and discounts	7,399		10,130	9,315
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	59
Total loans, net of unamortized deferred loan fees and discounts	5,959		8,456	7,595
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	10		6	7
Total loans, net of unamortized deferred loan fees and discounts	1,558		1,648	2,073
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	10		6	7
Total loans, net of unamortized deferred loan fees and discounts	1,128		1,167	1,575
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				23
Total loans, net of unamortized deferred loan fees and discounts	2,538		2,445	2,473
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				50
Total loans, net of unamortized deferred loan fees and discounts	1,440		1,674	1,720
Financial Asset Acquired with Credit Deterioration [Member] | Home Equity Loans [Member] | Consumer [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	429		439	455
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	$ 1		$ 42	$ 43