Loans and the Allowance for Credit Losses - Summary of Changes in Allowance for Credit Losses (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, beginning balance				$ 48,948				$ 45,284	$ 48,948	$ 45,284	$ 43,674
Allowance for loan commitments, beginning balance				741				574	741	574	571
Total beginning allowance for credit losses				49,689				45,858	49,689	45,858	44,245
Provision for loan losses									11,065	7,597	9,983
Provision for loan commitments									133	167	3
Total provision for credit losses	$ 1,824	$ 4,121	$ 2,747	2,507	$ 2,854	$ 1,035	$ 1,708	2,168	11,198	7,764	9,986
Charge-offs									(12,657)	(10,567)	(12,689)
Recoveries									5,073	6,634	4,316
Net recoveries (charge-offs)									(7,584)	(3,933)	(8,373)
Allowance for loan losses, ending balance	52,429				48,948				52,429	48,948	45,284
Allowance for loan commitments, ending balance	874				741				874	741	574
Total ending allowance for credit losses	53,303				49,689				53,303	49,689	45,858
Commercial Real Estate - Land and Construction [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, beginning balance				4,039				3,117	4,039	3,117	4,348
Allowance for loan commitments, beginning balance				169				119	169	119	151
Total beginning allowance for credit losses				4,208				3,236	4,208	3,236	4,499
Provision for loan losses									746	650	(1,259)
Provision for loan commitments									66	50	(32)
Total provision for credit losses									812	700	(1,291)
Charge-offs									(107)	(137)	(72)
Recoveries									271	409	100
Net recoveries (charge-offs)									164	272	28
Allowance for loan losses, ending balance	4,949				4,039				4,949	4,039	3,117
Allowance for loan commitments, ending balance	235				169				235	169	119
Total ending allowance for credit losses	5,184				4,208				5,184	4,208	3,236
Commercial Real Estate - Improved Property [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, beginning balance				20,848				21,166	20,848	21,166	18,628
Allowance for loan commitments, beginning balance				33				26	33	26	17
Total beginning allowance for credit losses				20,881				21,192	20,881	21,192	18,645
Provision for loan losses									2,560	(521)	4,386
Provision for loan commitments									(11)	7	9
Total provision for credit losses									2,549	(514)	4,395
Charge-offs									(3,867)	(1,090)	(2,381)
Recoveries									752	1,293	533
Net recoveries (charge-offs)									(3,115)	203	(1,848)
Allowance for loan losses, ending balance	20,293				20,848				20,293	20,848	21,166
Allowance for loan commitments, ending balance	22				33				22	33	26
Total ending allowance for credit losses	20,315				20,881				20,315	20,881	21,192
Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, beginning balance				12,114				9,414	12,114	9,414	8,412
Allowance for loan commitments, beginning balance				262				173	262	173	188
Total beginning allowance for credit losses				12,376				9,587	12,376	9,587	8,600
Provision for loan losses									2,714	3,430	2,733
Provision for loan commitments									49	89	(15)
Total provision for credit losses									2,763	3,519	2,718
Charge-offs									(1,816)	(1,830)	(2,669)
Recoveries									1,104	1,100	938
Net recoveries (charge-offs)									(712)	(730)	(1,731)
Allowance for loan losses, ending balance	14,116				12,114				14,116	12,114	9,414
Allowance for loan commitments, ending balance	311				262				311	262	173
Total ending allowance for credit losses	14,427				12,376				14,427	12,376	9,587
Deposit Overdraft [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, beginning balance				972				821	972	821	760
Total beginning allowance for credit losses				972				821	972	821	760
Provision for loan losses									1,664	1,146	1,001
Total provision for credit losses									1,664	1,146	1,001
Charge-offs									(1,659)	(1,374)	(1,293)
Recoveries									410	379	353
Net recoveries (charge-offs)									(1,249)	(995)	(940)
Allowance for loan losses, ending balance	1,387				972				1,387	972	821
Total ending allowance for credit losses	1,387				972				1,387	972	821
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, beginning balance				3,822				3,206	3,822	3,206	4,106
Allowance for loan commitments, beginning balance				12				7	12	7	9
Total beginning allowance for credit losses				3,834				3,213	3,834	3,213	4,115
Provision for loan losses									1,400	1,612	(175)
Provision for loan commitments									3	5	(2)
Total provision for credit losses									1,403	1,617	(177)
Charge-offs									(1,276)	(1,435)	(1,064)
Recoveries									365	439	339
Net recoveries (charge-offs)									(911)	(996)	(725)
Allowance for loan losses, ending balance	4,311				3,822				4,311	3,822	3,206
Allowance for loan commitments, ending balance	15				12				15	12	7
Total ending allowance for credit losses	4,326				3,834				4,326	3,834	3,213
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, beginning balance				2,797				3,063	2,797	3,063	3,998
Allowance for loan commitments, beginning balance				39				37	39	37	44
Total beginning allowance for credit losses				2,836				3,100	2,836	3,100	4,042
Provision for loan losses									1,130	1,142	1,231
Provision for loan commitments									2	2	(7)
Total provision for credit losses									1,132	1,144	1,224
Charge-offs									(2,719)	(3,508)	(3,989)
Recoveries									1,743	2,100	1,823
Net recoveries (charge-offs)									(976)	(1,408)	(2,166)
Allowance for loan losses, ending balance	2,951				2,797				2,951	2,797	3,063
Allowance for loan commitments, ending balance	41				39				41	39	37
Total ending allowance for credit losses	2,992				2,836				2,992	2,836	3,100
Home Equity [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, beginning balance				4,356				4,497	4,356	4,497	3,422
Allowance for loan commitments, beginning balance				226				212	226	212	162
Total beginning allowance for credit losses				$ 4,582				$ 4,709	4,582	4,709	3,584
Provision for loan losses									851	138	2,066
Provision for loan commitments									24	14	50
Total provision for credit losses									875	152	2,116
Charge-offs									(1,213)	(1,193)	(1,221)
Recoveries									428	914	230
Net recoveries (charge-offs)									(785)	(279)	(991)
Allowance for loan losses, ending balance	4,422				4,356				4,422	4,356	4,497
Allowance for loan commitments, ending balance	250				226				250	226	212
Total ending allowance for credit losses	$ 4,672				$ 4,582				$ 4,672	$ 4,582	$ 4,709