Loans and Leases - Schedule of Subsequently Defaulted TDRs (Detail) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018 USD ($) SecurityLoan	Sep. 30, 2017 USD ($) SecurityLoan	Sep. 30, 2018 USD ($) SecurityLoan	Sep. 30, 2017 USD ($) SecurityLoan
Accounts, Notes, Loans and Financing Receivable
Threshold period for loans in default (in days)			30 days
TDRs \| TDRs Occurring during the Period
Accounts, Notes, Loans and Financing Receivable
Number of Loans \| SecurityLoan	45	107	163	293
Pre-modification Outstanding Recorded Investment	$ 6,720	$ 23,821	$ 59,322	$ 49,445
Post-modification Outstanding Recorded Investment	$ 6,537	$ 24,586	$ 45,954	$ 51,517
Number of loans \| SecurityLoan	14	118	88	174
Recorded investment	$ 1,529	$ 9,446	$ 18,195	$ 20,988
TDRs \| Commercial Loans \| Commercial real estate - Construction \| TDRs Occurring during the Period
Accounts, Notes, Loans and Financing Receivable
Number of Loans \| SecurityLoan	0	2	1	2
Pre-modification Outstanding Recorded Investment	$ 0	$ 1,166	$ 1,950	$ 1,166
Post-modification Outstanding Recorded Investment	$ 0	$ 1,164	$ 976	$ 1,164
Number of loans \| SecurityLoan	0	2	0	2
Recorded investment	$ 0	$ 1,164	$ 0	$ 1,164
TDRs \| Commercial Loans \| Commercial real estate - owner-occupied \| TDRs Occurring during the Period
Accounts, Notes, Loans and Financing Receivable
Number of Loans \| SecurityLoan	1	3	8	5
Pre-modification Outstanding Recorded Investment	$ 2,312	$ 717	$ 15,233	$ 2,447
Post-modification Outstanding Recorded Investment	$ 2,312	$ 713	$ 13,373	$ 2,411
Number of loans \| SecurityLoan	1	4	6	8
Recorded investment	$ 929	$ 1,304	$ 10,101	$ 3,234
TDRs \| Commercial Loans \| Commercial real estate - non-owner-occupied \| TDRs Occurring during the Period
Accounts, Notes, Loans and Financing Receivable
Number of Loans \| SecurityLoan	6	10	13	21
Pre-modification Outstanding Recorded Investment	$ 1,818	$ 5,306	$ 3,228	$ 9,645
Post-modification Outstanding Recorded Investment	$ 1,790	$ 5,298	$ 3,064	$ 11,505
Number of loans \| SecurityLoan	1	11	6	16
Recorded investment	$ 7	$ 2,206	$ 1,084	$ 4,929
TDRs \| Commercial Loans \| Commercial and industrial \| TDRs Occurring during the Period
Accounts, Notes, Loans and Financing Receivable
Number of Loans \| SecurityLoan	9	11	32	44
Pre-modification Outstanding Recorded Investment	$ 829	$ 11,650	$ 32,827	$ 18,743
Post-modification Outstanding Recorded Investment	$ 804	$ 12,502	$ 22,769	$ 19,399
Number of loans \| SecurityLoan	2	16	12	31
Recorded investment	$ 127	$ 1,008	$ 3,632	$ 5,939
TDRs \| Residential Mortgage \| Residential mortgage \| TDRs Occurring during the Period
Accounts, Notes, Loans and Financing Receivable
Number of Loans \| SecurityLoan	3	7	9	16
Pre-modification Outstanding Recorded Investment	$ 257	$ 409	$ 898	$ 1,126
Post-modification Outstanding Recorded Investment	$ 255	$ 392	$ 837	$ 1,030
Number of loans \| SecurityLoan	0	13	8	18
Recorded investment	$ 0	$ 819	$ 912	$ 1,243
TDRs \| Consumer and Other Loans \| Consumer - Home equity \| TDRs Occurring during the Period
Accounts, Notes, Loans and Financing Receivable
Number of Loans \| SecurityLoan	15	38	47	99
Pre-modification Outstanding Recorded Investment	$ 1,152	$ 3,495	$ 4,130	$ 13,573
Post-modification Outstanding Recorded Investment	$ 1,124	$ 3,479	$ 4,047	$ 13,471
Number of loans \| SecurityLoan	4	23	17	34
Recorded investment	$ 380	$ 2,150	$ 1,978	$ 3,215
TDRs \| Consumer and Other Loans \| Consumer - Other \| TDRs Occurring during the Period
Accounts, Notes, Loans and Financing Receivable
Number of Loans \| SecurityLoan	11	36	53	106
Pre-modification Outstanding Recorded Investment	$ 352	$ 1,078	$ 1,056	$ 2,745
Post-modification Outstanding Recorded Investment	$ 252	$ 1,038	$ 888	$ 2,537
Number of loans \| SecurityLoan	6	49	39	65
Recorded investment	$ 86	$ 795	$ 488	$ 1,264

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-Name Accounting Standards Codification
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