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, 2018 USD ($) Modification	Jun. 30, 2017 USD ($) Modification	Jun. 30, 2018 USD ($) Modification	Jun. 30, 2017 USD ($) Modification
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	137	191	287	359
Pre-modification Recorded Investment	$ 58,013	$ 105,222	$ 128,015	$ 149,914
Post- modification	$ 58,909	$ 89,163	$ 131,531	$ 129,055
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	28	30	48	50
Pre-modification Recorded Investment	$ 7,200	$ 26,045	$ 13,980	$ 32,747
Post- modification	7,945	26,058	14,696	32,655
Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	20,384	24,087	70,040	37,734
Principal Deferral [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	7,376	11,782	13,200	14,773
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	5,556	6,505	6,853
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	$ 31,816	59,520	54,158	84,468
Combination of Concession Types [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Post- modification		$ 14,276	$ 927	$ 17,882
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	47	63	103	113
Pre-modification Recorded Investment	$ 41,390	$ 65,613	$ 89,384	$ 77,534
Post- modification	40,834	48,960	90,178	56,883
Commercial, Financial, Leasing, etc. [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	9,673	8,172	45,346	12,561
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	5,556	6,111	6,362
Commercial, Financial, Leasing, etc. [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 25,021	$ 35,232	$ 38,068	$ 37,960
Residential Builder and Developer [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification				3
Pre-modification Recorded Investment				$ 12,291
Post- modification				10,879
Residential Builder and Developer [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification				$ 10,879
Other Commercial Construction [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification		1	1	2
Pre-modification Recorded Investment		$ 66	$ 752	$ 168
Post- modification		66	746	168
Other Commercial Construction [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification		$ 66	$ 746	$ 168
Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	30	30	77	71
Pre-modification Recorded Investment	$ 7,951	$ 7,956	$ 20,587	$ 17,336
Post- modification	8,580	8,468	22,427	18,416
Residential [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	2,814	2,982	9,759	8,575
Residential [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 5,766	$ 5,486	$ 12,668	$ 9,841
Residential Limited Documentation [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	3	7	5	13
Pre-modification Recorded Investment	$ 584	$ 1,831	$ 879	$ 3,209
Post- modification	658	1,895	1,043	3,420
Residential Limited Documentation [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	200	235	467	235
Residential Limited Documentation [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 458	$ 1,660	$ 576	$ 3,185
Home Equity Lines and Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	10	35	24	60
Pre-modification Recorded Investment	$ 555	$ 3,229	$ 1,903	$ 5,731
Post- modification	559	3,234	1,911	5,736
Home Equity Lines and Loans [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification		416	4	579
Home Equity Lines and Loans [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Post- modification				491
Home Equity Lines and Loans [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 559	$ 2,818	$ 1,907	$ 4,666
Other [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification		3	2	5
Pre-modification Recorded Investment		$ 54	$ 49	$ 80
Post- modification		54	49	80
Other [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification		$ 54	$ 49	$ 80
Automobile [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	19	22	27	42
Pre-modification Recorded Investment	$ 333	$ 428	$ 481	$ 818
Post- modification	333	428	481	818
Automobile [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	321	380	469	763
Automobile [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 12	$ 48	$ 12	$ 55