Loans and Leases and the Allowance for Credit Losses - Loan Modification Activities that were Considered Troubled Debt Restructurings (Detail) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019 USD ($) Modification	Jun. 30, 2018 USD ($) Modification	Jun. 30, 2019 USD ($) Modification	Jun. 30, 2018 USD ($) Modification
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	93	137	225	287
Pre-modification Recorded Investment	$ 23,577	$ 58,013	$ 70,114	$ 128,015
Post- modification	$ 23,958	$ 58,909	$ 70,249	$ 131,531
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	14	28	29	48
Pre-modification Recorded Investment	$ 10,340	$ 7,200	$ 19,581	$ 13,980
Post- modification	10,218	7,945	19,172	14,696
Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	7,669	20,384	18,593	70,040
Principal Deferral [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	2,577	7,376	3,564	13,200
Interest Rate Reduction [Member]
Financing Receivable, Modifications [Line Items]
Post- modification		204		828
Interest Rate Reduction [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Post- modification		175		175
Other [Member]
Financing Receivable, Modifications [Line Items]
Post- modification		6,505		6,505
Other [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Post- modification		394		394
Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	16,289	$ 31,816	51,656	54,158
Combination of Concession Types [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 7,641		$ 15,608	$ 927
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	24	47	89	103
Pre-modification Recorded Investment	$ 2,597	$ 41,390	$ 33,212	$ 89,384
Post- modification	2,558	40,834	33,302	90,178
Commercial, Financial, Leasing, etc. [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	667	9,673	7,141	45,346
Commercial, Financial, Leasing, etc. [Member] | Interest Rate Reduction [Member]
Financing Receivable, Modifications [Line Items]
Post- modification		29		653
Commercial, Financial, Leasing, etc. [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Post- modification		6,111		6,111
Commercial, Financial, Leasing, etc. [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 1,891	$ 25,021	$ 26,161	$ 38,068
Residential Builder and Developer [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification			2
Pre-modification Recorded Investment			$ 1,330
Post- modification			1,068
Residential Builder and Developer [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification			$ 1,068
Other Commercial Construction [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	1		2	1
Pre-modification Recorded Investment	$ 1,038		$ 1,456	$ 752
Post- modification	1,033		1,399	746
Other Commercial Construction [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification				$ 746
Other Commercial Construction [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 1,033		$ 1,399
Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	26	30	43	77
Pre-modification Recorded Investment	$ 7,513	$ 7,951	$ 11,329	$ 20,587
Post- modification	8,042	8,580	12,066	22,427
Residential [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	4,008	2,814	5,759	9,759
Residential [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 4,034	$ 5,766	$ 6,307	$ 12,668
Residential Limited Documentation [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	2	3	3	5
Pre-modification Recorded Investment	$ 612	$ 584	$ 848	$ 879
Post- modification	625	658	864	1,043
Residential Limited Documentation [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	160	200	399	467
Residential Limited Documentation [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 465	$ 458	$ 465	$ 576
Home Equity Lines and Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	13	10	20	24
Pre-modification Recorded Investment	$ 1,273	$ 555	$ 1,749	$ 1,903
Post- modification	1,278	559	1,769	1,911
Home Equity Lines and Loans [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	53		90	4
Home Equity Lines and Loans [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 1,225	$ 559	$ 1,679	$ 1,907
Automobile [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	12	19	32	27
Pre-modification Recorded Investment	$ 189	$ 333	$ 506	$ 481
Post- modification	189	333	506	481
Automobile [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 189	321	469	469
Automobile [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification		$ 12	$ 37	$ 12
Recreational Finance [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	1		5	2
Pre-modification Recorded Investment	$ 15		$ 103	$ 49
Post- modification	15		103	49
Recreational Finance [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 15		$ 103	$ 49