Loans and Leases and the Allowance for Credit Losses - Loan Modification Activities that were Considered Troubled Debt Restructurings (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($) Modification	Mar. 31, 2018 USD ($) Modification
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	132	150
Pre-modification Recorded Investment	$ 46,537	$ 70,002
Post- modification	$ 46,291	$ 72,622
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	15	20
Pre-modification Recorded Investment	$ 9,241	$ 6,780
Post- modification	8,954	6,751
Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	10,924	49,656
Principal Deferral [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	987	5,824
Interest Rate Reduction [Member]
Financing Receivable, Modifications [Line Items]
Post- modification		624
Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	35,367	22,342
Combination of Concession Types [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 7,967	$ 927
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	65	56
Pre-modification Recorded Investment	$ 30,615	$ 47,994
Post- modification	30,744	49,344
Commercial, Financial, Leasing, etc. [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	6,474	35,673
Commercial, Financial, Leasing, etc. [Member] | Interest Rate Reduction [Member]
Financing Receivable, Modifications [Line Items]
Post- modification		624
Commercial, Financial, Leasing, etc. [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 24,270	$ 13,047
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	1
Pre-modification Recorded Investment	$ 418	$ 752
Post- modification	366	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	$ 366
Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	17	47
Pre-modification Recorded Investment	$ 3,816	$ 12,636
Post- modification	4,024	13,847
Residential [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	1,751	6,945
Residential [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 2,273	$ 6,902
Residential Limited Documentation [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	1	2
Pre-modification Recorded Investment	$ 236	$ 295
Post- modification	239	385
Residential Limited Documentation [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 239	267
Residential Limited Documentation [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification		$ 118
Home Equity Lines and Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	7	14
Pre-modification Recorded Investment	$ 476	$ 1,348
Post- modification	491	1,352
Home Equity Lines and Loans [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	37	4
Home Equity Lines and Loans [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 454	$ 1,348
Automobile [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	20	8
Pre-modification Recorded Investment	$ 317	$ 148
Post- modification	317	148
Automobile [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	280	$ 148
Automobile [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 37
Recreational Finance [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	4	2
Pre-modification Recorded Investment	$ 88	$ 49
Post- modification	88	49
Recreational Finance [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 88	$ 49