Loans and the Allowance for Credit Losses - Allowance for Credit Losses and Recorded Investments in Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans individually evaluated for impairment	$ 1,501
Allowance for loans collectively evaluated for impairment	52,816	$ 48,948
Allowance for loan commitments	1,639	741	$ 684	$ 574
Total allowance for credit losses	55,956	49,689	49,586	45,858
Individually evaluated for impairment	11,042
Collectively evaluated for impairment	7,735,160	7,646,540
Acquired with deteriorated credit quality	10,550	9,741
Total loans	7,756,752	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	4,042	4,039
Allowance for loan commitments	195	169	186	119
Total allowance for credit losses	4,237	4,208	4,355	3,236
Collectively evaluated for impairment	510,162	527,737
Acquired with deteriorated credit quality	242	335
Total loans	510,404	528,072
Commercial Real Estate - Improved Property [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans individually evaluated for impairment	1,471
Allowance for loans collectively evaluated for impairment	22,422	20,848
Allowance for loan commitments	24	33	23	26
Total allowance for credit losses	23,917	20,881	20,847	21,192
Individually evaluated for impairment	5,388
Collectively evaluated for impairment	3,330,959	3,319,672
Acquired with deteriorated credit quality	7,902	5,951
Total loans	3,344,249	3,325,623
Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans individually evaluated for impairment	10
Allowance for loans collectively evaluated for impairment	13,778	12,114
Allowance for loan commitments	1,104	262	205	173
Total allowance for credit losses	14,892	12,376	12,256	9,587
Individually evaluated for impairment	185
Collectively evaluated for impairment	1,331,248	1,264,560
Acquired with deteriorated credit quality	842	900
Total loans	1,332,275	1,265,460
Deposit Overdrafts [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans collectively evaluated for impairment	1,496	972
Total allowance for credit losses	1,496	972	997	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	3,773	3,822
Allowance for loan commitments	15	12	9	7
Total allowance for credit losses	3,800	3,834	3,784	3,213
Individually evaluated for impairment	4,662
Collectively evaluated for impairment	1,632,348	1,609,177
Acquired with deteriorated credit quality	1,564	2,430
Total loans	1,638,574	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	2,747	2,797
Allowance for loan commitments	38	39	40	37
Total allowance for credit losses	2,786	2,836	2,836	3,100
Individually evaluated for impairment	61
Collectively evaluated for impairment	343,444	326,063
Acquired with deteriorated credit quality		125
Total loans	343,505	326,188
Home Equity [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans individually evaluated for impairment	7
Allowance for loans collectively evaluated for impairment	4,558	4,356
Allowance for loan commitments	263	226	221	212
Total allowance for credit losses	4,828	4,582	$ 4,511	$ 4,709
Individually evaluated for impairment	746
Collectively evaluated for impairment	586,999	599,331
Total loans	$ 587,745	$ 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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