Loans and Leases and the Allowance for Credit Losses - Loan Modification Activities that were Considered Troubled Debt Restructurings (Detail) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($) Modification	Sep. 30, 2019 USD ($) Modification	Sep. 30, 2020 USD ($) Modification	Sep. 30, 2019 USD ($) Modification
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	1,085	97	3,575	322
Pre-modification Recorded Investment	$ 73,071	$ 16,466	$ 292,445	$ 86,580
Post- modification	73,598	16,845	283,415	87,094
Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	35,178	5,388	117,336	23,981
Interest Rate Reduction [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	470		803
Other [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	30		36,435
Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 37,920	$ 11,457	$ 128,841	$ 63,113
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	112	26	279	115
Pre-modification Recorded Investment	$ 35,037	$ 6,145	$ 102,865	$ 39,357
Post- modification	34,955	6,107	101,678	39,409
Commercial, Financial, Leasing, etc. [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	7,145	1,441	29,762	8,582
Commercial, Financial, Leasing, etc. [Member] | Interest Rate Reduction [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	298		298
Commercial, Financial, Leasing, etc. [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Post- modification			31,605
Commercial, Financial, Leasing, etc. [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 27,512	$ 4,666	$ 40,013	$ 30,827
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	50	9	106	38
Pre-modification Recorded Investment	$ 13,293	$ 2,986	$ 94,807	$ 22,567
Post- modification	13,308	2,972	82,623	22,144
Commercial Real Estate [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	12,506	383	24,372	3,947
Commercial Real Estate [Member] | Interest Rate Reduction [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	172		505
Commercial Real Estate [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	30		4,830
Commercial Real Estate [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 600	$ 2,589	$ 52,916	$ 18,197
Residential Builder and Developer [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification			1	2
Pre-modification Recorded Investment			$ 91	$ 1,330
Post- modification			90	1,068
Residential Builder and Developer [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification				$ 1,068
Residential Builder and Developer [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification			$ 90
Other Commercial Construction [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification				2
Pre-modification Recorded Investment				$ 1,456
Post- modification				1,399
Other Commercial Construction [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification				$ 1,399
Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	30	20	82	63
Pre-modification Recorded Investment	$ 8,544	$ 5,161	$ 27,594	$ 16,490
Post- modification	9,133	5,581	30,991	17,647
Residential [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	5,517	3,046	11,865	8,805
Residential [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 3,616	$ 2,535	$ 19,126	$ 8,842
Home Equity Lines and Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	33	12	159	32
Pre-modification Recorded Investment	$ 3,410	$ 1,392	$ 11,719	$ 3,141
Post- modification	3,415	1,399	11,745	3,168
Home Equity Lines and Loans [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	129		688	90
Home Equity Lines and Loans [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 3,286	$ 1,399	$ 11,057	$ 3,078
Recreational Finance [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	74	3	348	8
Pre-modification Recorded Investment	$ 2,734	$ 61	$ 13,619	$ 164
Post- modification	2,734	61	13,619	164
Recreational Finance [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 2,734	$ 61	$ 13,619	$ 164
Automobile [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	403	26	1,873	58
Pre-modification Recorded Investment	$ 7,007	$ 485	$ 33,541	$ 991
Post- modification	7,007	485	33,541	991
Automobile [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	7,005	457	33,539	926
Automobile [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 2	$ 28	$ 2	$ 65
Other [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	383		718
Pre-modification Recorded Investment	$ 3,046		$ 5,229
Post- modification	3,046		5,229
Other [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	142		824
Other [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 2,904		$ 4,405
Residential Limited Documentation [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification		1	9	4
Pre-modification Recorded Investment		$ 236	$ 2,980	$ 1,084
Post- modification		240	3,899	1,104
Residential Limited Documentation [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification			2,667	399
Residential Limited Documentation [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification		$ 240	$ 1,232	$ 705