Allowance for Loan Losses - Schedule Credit Quality Indicators (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	$ 4,307,366	$ 4,022,014	$ 3,015,165
Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	3,328,290	3,143,100	2,300,322
Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	445,542	418,982	356,874
Commercial
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	283,707	276,548	220,412
Construction
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	249,827	183,384	137,557
Residential 1-4 family | Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
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]
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]
Total loans, net of unamortized deferred loan fees and discounts	82,656	55,721	25,155
Originated
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	3,487,695	2,981,456
Originated | Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	2,594,318	2,254,777
Originated | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	392,693	351,133
Originated | Commercial
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	262,581	228,635
Originated | Construction
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	238,103	146,911
Originated | Residential 1-4 family | Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	373,101	343,796
Originated | Home equity loans | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	25,343	32,660
Originated | Other | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	67,896	34,020
PNCI
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	809,255	1,026,335
PNCI | Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	727,238	878,193
PNCI | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	51,644	66,201
PNCI | Commercial
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	18,649	45,468
PNCI | Construction
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	11,724	36,473
PNCI | Residential 1-4 family | Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	134,994	169,792
PNCI | Home equity loans | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	2,829	3,585
PNCI | Other | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	14,758	21,659
Commercial | Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	2,818,782	2,627,838	1,914,896
Commercial | Construction
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	46,861	62,088	69,627
Commercial | Originated | Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	2,221,217	1,910,981
Commercial | Originated | Construction
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	46,422	56,208
Commercial | PNCI | Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	592,244	708,401
Commercial | PNCI | Construction
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	439	5,880
Home equity lines of credit | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	334,300	326,577	288,688
Home equity lines of credit | Originated | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	299,454	284,453
Home equity lines of credit | PNCI | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	34,057	40,957
Residential | Construction
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	202,966	121,296	$ 67,930
Residential | Originated | Construction
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	191,681	90,703
Residential | PNCI | Construction
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	11,285	30,593
Pass | Originated
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	3,427,375	2,904,603
Pass | Originated | Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	2,552,110	2,198,816
Pass | Originated | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	383,172	342,386
Pass | Originated | Commercial
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	254,554	217,126
Pass | Originated | Construction
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	237,539	146,275
Pass | Originated | Residential 1-4 family | Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	366,149	337,189
Pass | Originated | Home equity loans | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	22,318	29,289
Pass | Originated | Other | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	67,422	33,606
Pass | PNCI
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	792,033	1,014,950
Pass | PNCI | Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	716,649	869,776
Pass | PNCI | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	49,260	63,674
Pass | PNCI | Commercial
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	18,602	45,027
Pass | PNCI | Construction
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	7,522	36,473
Pass | PNCI | Residential 1-4 family | Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	131,820	167,908
Pass | PNCI | Home equity loans | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	2,774	3,413
Pass | PNCI | Other | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	14,390	21,481
Pass | Commercial | Originated | Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	2,185,961	1,861,627
Pass | Commercial | Originated | Construction
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	46,105	55,863
Pass | Commercial | PNCI | Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	584,829	701,868
Pass | Commercial | PNCI | Construction
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	439	5,880
Pass | Home equity lines of credit | Originated | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	293,432	279,491
Pass | Home equity lines of credit | PNCI | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	32,096	38,780
Pass | Residential | Originated | Construction
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	191,434	90,412
Pass | Residential | PNCI | Construction
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	7,083	30,593
Special Mention | Originated
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	36,022	45,415
Special Mention | Originated | Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	26,982	35,207
Special Mention | Originated | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	4,897	3,704
Special Mention | Originated | Commercial
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	3,826	6,127
Special Mention | Originated | Construction
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	317	377
Special Mention | Originated | Residential 1-4 family | Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	2,497	1,724
Special Mention | Originated | Home equity loans | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	1,192	1,054
Special Mention | Originated | Other | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	373	341
Special Mention | PNCI
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	8,196	5,863
Special Mention | PNCI | Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	2,790	4,171
Special Mention | PNCI | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	1,203	1,371
Special Mention | PNCI | Commercial
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	1	321
Special Mention | PNCI | Construction
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	4,202
Special Mention | PNCI | Residential 1-4 family | Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	2,217	1,086
Special Mention | PNCI | Home equity loans | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	0	74
Special Mention | PNCI | Other | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	346	173
Special Mention | Commercial | Originated | Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	24,485	33,483
Special Mention | Commercial | Originated | Construction
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	317	345
Special Mention | Commercial | PNCI | Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	573	3,085
Special Mention | Commercial | PNCI | Construction
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	0
Special Mention | Home equity lines of credit | Originated | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	3,332	2,309
Special Mention | Home equity lines of credit | PNCI | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	857	1,124
Special Mention | Residential | Originated | Construction
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	0	32
Special Mention | Residential | PNCI | Construction
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	4,202
Substandard | Originated
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	24,298	31,438
Substandard | Originated | Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	15,226	20,754
Substandard | Originated | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	4,624	5,043
Substandard | Originated | Commercial
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	4,201	5,382
Substandard | Originated | Construction
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	247	259
Substandard | Originated | Residential 1-4 family | Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	4,455	4,883
Substandard | Originated | Home equity loans | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	1,833	2,317
Substandard | Originated | Other | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	101	73
Substandard | PNCI
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	9,026	5,522
Substandard | PNCI | Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	7,799	4,246
Substandard | PNCI | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	1,181	1,156
Substandard | PNCI | Commercial
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	46	120
Substandard | PNCI | Construction
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	0
Substandard | PNCI | Residential 1-4 family | Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	957	798
Substandard | PNCI | Home equity loans | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	55	98
Substandard | PNCI | Other | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	22	5
Substandard | Commercial | Originated | Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	10,771	15,871
Substandard | Commercial | Originated | Construction
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	0
Substandard | Commercial | PNCI | Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	6,842	3,448
Substandard | Commercial | PNCI | Construction
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	0
Substandard | Home equity lines of credit | Originated | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	2,690	2,653
Substandard | Home equity lines of credit | PNCI | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	1,104	1,053
Substandard | Residential | Originated | Construction
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	247	$ 259
Substandard | Residential | PNCI | Construction
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	$ 0