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, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Loans and Leases Receivable Disclosure [Line Items]
Loans pooled for evaluation	$ 29,675	$ 30,266	$ 27,352
Individually evaluated for impairment	935	2,194	2,699
Total allowance for loan losses	30,616	32,582	30,323	$ 32,503
Loans pooled for evaluation	4,277,033	3,979,744	2,971,371
Individually evaluated for impairment	19,917	28,047	28,234
Total loans, net of unamortized deferred loan fees and discounts	4,307,366	4,022,014	3,015,165
Commercial
Loans and Leases Receivable Disclosure [Line Items]
Loans pooled for evaluation		663
Total allowance for loan losses		663
Residential
Loans and Leases Receivable Disclosure [Line Items]
Loans pooled for evaluation		1,834
Total allowance for loan losses		1,834
Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Loans pooled for evaluation	14,174	15,357	13,283
Individually evaluated for impairment	127	147	260
Total allowance for loan losses	14,301	15,620	13,758	14,265
Loans pooled for evaluation	3,307,833	3,116,086	2,271,165
Individually evaluated for impairment	13,723	16,884	19,209
Total loans, net of unamortized deferred loan fees and discounts	3,328,290	3,143,100	2,300,322
Mortgage Loans on Real Estate | Commercial
Loans and Leases Receivable Disclosure [Line Items]
Loans pooled for evaluation	11,917	12,737	11,351
Individually evaluated for impairment	78	91	30
Total allowance for loan losses	11,995	12,944	11,441	11,517
Loans pooled for evaluation	2,804,812	2,606,819	1,892,422
Individually evaluated for impairment	8,649	12,563	13,911
Total loans, net of unamortized deferred loan fees and discounts	2,818,782	2,627,838	1,914,896
Consumer
Loans and Leases Receivable Disclosure [Line Items]
Loans pooled for evaluation	7,594	8,103	7,619
Individually evaluated for impairment	178	266	591
Total allowance for loan losses	7,778	8,375	8,227	10,310
Loans pooled for evaluation	440,473	411,389	349,431
Individually evaluated for impairment	3,864	5,945	4,415
Total loans, net of unamortized deferred loan fees and discounts	445,542	418,982	356,874
Consumer | Home equity lines of credit
Loans and Leases Receivable Disclosure [Line Items]
Loans pooled for evaluation	5,451	5,838	5,356
Individually evaluated for impairment	115	198	427
Total allowance for loan losses	5,572	6,042	5,800	7,044
Loans pooled for evaluation	331,437	322,764	283,502
Individually evaluated for impairment	2,074	2,646	2,688
Total loans, net of unamortized deferred loan fees and discounts	334,300	326,577	288,688
Commercial
Loans and Leases Receivable Disclosure [Line Items]
Loans pooled for evaluation	4,519	4,309	4,624
Individually evaluated for impairment	630	1,781	1,848
Total allowance for loan losses	5,149	6,090	6,512	5,831
Loans pooled for evaluation	278,900	268,885	213,358
Individually evaluated for impairment	2,330	5,218	4,470
Total loans, net of unamortized deferred loan fees and discounts	283,707	276,548	220,412
Construction
Loans and Leases Receivable Disclosure [Line Items]
Loans pooled for evaluation	3,388	2,497	1,826
Individually evaluated for impairment	0		0
Total allowance for loan losses	3,388	2,497	1,826	2,097
Loans pooled for evaluation	249,827	183,384	137,417
Individually evaluated for impairment	0	0	140
Total loans, net of unamortized deferred loan fees and discounts	249,827	183,384	137,557
Construction | Commercial
Loans and Leases Receivable Disclosure [Line Items]
Loans pooled for evaluation	318		642
Individually evaluated for impairment	0
Total allowance for loan losses	318	663	642	680
Loans pooled for evaluation	46,861	62,088	69,627
Individually evaluated for impairment	0
Total loans, net of unamortized deferred loan fees and discounts	46,861	62,088	69,627
Construction | Residential
Loans and Leases Receivable Disclosure [Line Items]
Loans pooled for evaluation	3,070		1,184
Individually evaluated for impairment	0
Total allowance for loan losses	3,070	1,834	1,184	1,417
Loans pooled for evaluation	202,966	121,296	67,790
Individually evaluated for impairment	0		140
Total loans, net of unamortized deferred loan fees and discounts	202,966	121,296	67,930
Residential 1-4 family | Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Loans pooled for evaluation	2,257	2,620	1,932
Individually evaluated for impairment	49	56	230
Total allowance for loan losses	2,306	2,676	2,317	2,748
Loans pooled for evaluation	503,021	509,267	378,743
Individually evaluated for impairment	5,074	4,321	5,298
Total loans, net of unamortized deferred loan fees and discounts	509,508	515,262	385,426
Home equity loans | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Loans pooled for evaluation	567	1,486	1,734
Individually evaluated for impairment	44	54	107
Total allowance for loan losses	611	1,540	1,841	2,644
Loans pooled for evaluation	26,522	33,142	41,076
Individually evaluated for impairment	1,650	3,103	1,470
Total loans, net of unamortized deferred loan fees and discounts	28,586	36,684	43,031
Other | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Loans pooled for evaluation	1,576	779	529
Individually evaluated for impairment	19	14	57
Total allowance for loan losses	1,595	793	586	$ 622
Loans pooled for evaluation	82,514	55,483	24,853
Individually evaluated for impairment	140	196	257
Total loans, net of unamortized deferred loan fees and discounts	82,656	55,721	25,155
Financial Asset Acquired with Credit Deterioration
Loans and Leases Receivable Disclosure [Line Items]
Loans acquired with deteriorated credit quality	6	122	272
Total loans, net of unamortized deferred loan fees and discounts	10,416	14,223	15,560
Financial Asset Acquired with Credit Deterioration | Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Loans acquired with deteriorated credit quality	0	116	215
Total loans, net of unamortized deferred loan fees and discounts	6,734	10,130	9,948
Financial Asset Acquired with Credit Deterioration | Mortgage Loans on Real Estate | Commercial
Loans and Leases Receivable Disclosure [Line Items]
Loans acquired with deteriorated credit quality	0	116	60
Total loans, net of unamortized deferred loan fees and discounts	5,321	8,456	8,563
Financial Asset Acquired with Credit Deterioration | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Loans acquired with deteriorated credit quality	6	6	17
Total loans, net of unamortized deferred loan fees and discounts	1,205	1,648	3,028
Financial Asset Acquired with Credit Deterioration | Consumer | Home equity lines of credit
Loans and Leases Receivable Disclosure [Line Items]
Loans acquired with deteriorated credit quality	6	6	17
Total loans, net of unamortized deferred loan fees and discounts	789	1,167	2,498
Financial Asset Acquired with Credit Deterioration | Commercial
Loans and Leases Receivable Disclosure [Line Items]
Loans acquired with deteriorated credit quality	0		40
Total loans, net of unamortized deferred loan fees and discounts	2,477	2,445	2,584
Financial Asset Acquired with Credit Deterioration | Construction
Loans and Leases Receivable Disclosure [Line Items]
Loans acquired with deteriorated credit quality	0		0
Total loans, net of unamortized deferred loan fees and discounts	0	0	0
Financial Asset Acquired with Credit Deterioration | Construction | Commercial
Loans and Leases Receivable Disclosure [Line Items]
Loans acquired with deteriorated credit quality	0
Total loans, net of unamortized deferred loan fees and discounts	0
Financial Asset Acquired with Credit Deterioration | Construction | Residential
Loans and Leases Receivable Disclosure [Line Items]
Loans acquired with deteriorated credit quality	0
Total loans, net of unamortized deferred loan fees and discounts	0
Financial Asset Acquired with Credit Deterioration | Residential 1-4 family | Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Loans acquired with deteriorated credit quality	0		155
Total loans, net of unamortized deferred loan fees and discounts	1,413	1,674	1,385
Financial Asset Acquired with Credit Deterioration | Home equity loans | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Loans acquired with deteriorated credit quality	0
Total loans, net of unamortized deferred loan fees and discounts	414	439	485
Financial Asset Acquired with Credit Deterioration | Other | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Loans acquired with deteriorated credit quality	0
Total loans, net of unamortized deferred loan fees and discounts	$ 2	$ 42	$ 45