Loans and the Allowance for Credit Losses - Summary of Changes in Allowance for Credit Losses (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, beginning balance			$ 45,284	$ 43,674
Allowance for loan commitments, beginning balance			574	571
Total beginning allowance for credit losses			45,858	44,245
Provision for loan losses			3,843	5,068
Provision for loan commitments			33	26
Total provision for credit losses	$ 1,708	$ 2,383	3,876	5,094
Charge-offs			(4,959)	(6,240)
Recoveries			3,470	2,407
Net charge-offs			(1,489)	(3,833)
Allowance for loan losses, ending balance	47,638	44,909	47,638	44,909
Allowance for loan commitments, ending balance	607	597	607	597
Total ending allowance for credit losses	48,245	45,506	48,245	45,506
Commercial Real Estate - Land and Construction [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, beginning balance			3,117	4,348
Allowance for loan commitments, beginning balance			119	151
Total beginning allowance for credit losses			3,236	4,499
Provision for loan losses			1,465	1,039
Provision for loan commitments			44	14
Total provision for credit losses			1,509	1,053
Charge-offs			(136)
Recoveries			264	70
Net charge-offs			128	70
Allowance for loan losses, ending balance	4,710	5,457	4,710	5,457
Allowance for loan commitments, ending balance	163	165	163	165
Total ending allowance for credit losses	4,873	5,622	4,873	5,622
Commercial Real Estate - Improved Property [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, beginning balance			21,166	18,628
Allowance for loan commitments, beginning balance			26	17
Total beginning allowance for credit losses			21,192	18,645
Provision for loan losses			(1,774)	558
Provision for loan commitments			(8)	1
Total provision for credit losses			(1,782)	559
Charge-offs			(692)	(1,574)
Recoveries			776	376
Net charge-offs			84	(1,198)
Allowance for loan losses, ending balance	19,476	17,988	19,476	17,988
Allowance for loan commitments, ending balance	18	18	18	18
Total ending allowance for credit losses	19,494	18,006	19,494	18,006
Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, beginning balance			9,414	8,412
Allowance for loan commitments, beginning balance			173	188
Total beginning allowance for credit losses			9,587	8,600
Provision for loan losses			2,100	1,552
Provision for loan commitments			2	(9)
Total provision for credit losses			2,102	1,543
Charge-offs			(616)	(1,205)
Recoveries			636	475
Net charge-offs			20	(730)
Allowance for loan losses, ending balance	11,534	9,234	11,534	9,234
Allowance for loan commitments, ending balance	175	179	175	179
Total ending allowance for credit losses	11,709	9,413	11,709	9,413
Deposit Overdraft [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, beginning balance			821	760
Total beginning allowance for credit losses			821	760
Provision for loan losses			439	444
Total provision for credit losses			439	444
Charge-offs			(541)	(611)
Recoveries			197	181
Net charge-offs			(344)	(430)
Allowance for loan losses, ending balance	916	774	916	774
Total ending allowance for credit losses	916	774	916	774
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, beginning balance			3,206	4,106
Allowance for loan commitments, beginning balance			7	9
Total beginning allowance for credit losses			3,213	4,115
Provision for loan losses			944	39
Provision for loan commitments			2	1
Total provision for credit losses			946	40
Charge-offs			(509)	(592)
Recoveries			252	164
Net charge-offs			(257)	(428)
Allowance for loan losses, ending balance	3,893	3,717	3,893	3,717
Allowance for loan commitments, ending balance	9	10	9	10
Total ending allowance for credit losses	3,902	3,727	3,902	3,727
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, beginning balance			3,063	3,998
Allowance for loan commitments, beginning balance			37	44
Total beginning allowance for credit losses			3,100	4,042
Provision for loan losses			615	970
Provision for loan commitments				2
Total provision for credit losses			615	972
Charge-offs			(1,793)	(1,965)
Recoveries			1,066	990
Net charge-offs			(727)	(975)
Allowance for loan losses, ending balance	2,951	3,993	2,951	3,993
Allowance for loan commitments, ending balance	37	46	37	46
Total ending allowance for credit losses	2,988	4,039	2,988	4,039
Home Equity [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, beginning balance			4,497	3,422
Allowance for loan commitments, beginning balance			212	162
Total beginning allowance for credit losses			4,709	3,584
Provision for loan losses			54	466
Provision for loan commitments			(7)	17
Total provision for credit losses			47	483
Charge-offs			(672)	(293)
Recoveries			279	151
Net charge-offs			(393)	(142)
Allowance for loan losses, ending balance	4,158	3,746	4,158	3,746
Allowance for loan commitments, ending balance	205	179	205	179
Total ending allowance for credit losses	$ 4,363	$ 3,925	$ 4,363	$ 3,925