Loans and the Allowance for Credit Losses - Allowance for Credit Losses and Recorded Investments in Loans (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans individually evaluated for impairment	$ 1,511
Allowance for loans collectively evaluated for impairment	49,348	$ 48,948
Allowance for loan commitments	1,766	741	$ 607	$ 574
Total allowance for credit losses	52,625	49,689	48,245	45,858
Individually evaluated for impairment	11,267
Collectively evaluated for impairment	7,715,955	7,646,540
Acquired with deteriorated credit quality	10,632	9,741
Total loans	7,737,854	7,656,281
Commercial Real Estate - Land and Construction [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans collectively evaluated for impairment	3,701	4,039
Allowance for loan commitments	187	169	163	119
Total allowance for credit losses	3,888	4,208	4,873	3,236
Collectively evaluated for impairment	482,804	527,737
Acquired with deteriorated credit quality	242	335
Total loans	483,046	528,072
Commercial Real Estate - Improved Property [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans individually evaluated for impairment	1,479
Allowance for loans collectively evaluated for impairment	20,888	20,848
Allowance for loan commitments	24	33	18	26
Total allowance for credit losses	22,391	20,881	19,494	21,192
Individually evaluated for impairment	5,157
Collectively evaluated for impairment	3,381,541	3,319,672
Acquired with deteriorated credit quality	7,889	5,951
Total loans	3,394,587	3,325,623
Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans individually evaluated for impairment	11
Allowance for loans collectively evaluated for impairment	12,876	12,114
Allowance for loan commitments	1,257	262	175	173
Total allowance for credit losses	14,144	12,376	11,709	9,587
Individually evaluated for impairment	192
Collectively evaluated for impairment	1,299,528	1,264,560
Acquired with deteriorated credit quality	857	900
Total loans	1,300,577	1,265,460
Deposit Overdraft [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans collectively evaluated for impairment	1,446	972
Total allowance for credit losses	1,446	972	916	821
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans individually evaluated for impairment	12
Allowance for loans collectively evaluated for impairment	3,443	3,822
Allowance for loan commitments	13	12	9	7
Total allowance for credit losses	3,468	3,834	3,902	3,213
Individually evaluated for impairment	4,922
Collectively evaluated for impairment	1,627,047	1,609,177
Acquired with deteriorated credit quality	1,644	2,430
Total loans	1,633,613	1,611,607
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans individually evaluated for impairment	1
Allowance for loans collectively evaluated for impairment	2,681	2,797
Allowance for loan commitments	36	39	37	37
Total allowance for credit losses	2,718	2,836	2,988	3,100
Individually evaluated for impairment	74
Collectively evaluated for impairment	335,654	326,063
Acquired with deteriorated credit quality		125
Total loans	335,728	326,188
Home Equity [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans individually evaluated for impairment	8
Allowance for loans collectively evaluated for impairment	4,313	4,356
Allowance for loan commitments	249	226	205	212
Total allowance for credit losses	4,570	4,582	$ 4,363	$ 4,709
Individually evaluated for impairment	922
Collectively evaluated for impairment	589,381	599,331
Total loans	$ 590,303	$ 599,331

The recorded balance, net of any applicable reductions (for example, unamortized accretable yield and allowance for loan losses). This relates to loans not accounted for debt securities with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

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