Loans and Leases and the Allowance for Credit Losses - Loan Modification Activities that were Considered Troubled Debt Restructurings (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) Modification	Dec. 31, 2016 USD ($) Modification	Dec. 31, 2015 USD ($) Modification
Financing Receivable Modifications [Line Items]
Number of modifications | Modification	654	739	817
Pre- modification recorded investment	$ 216,063	$ 279,696	$ 204,800
Post- modification	$ 191,522	$ 268,415	$ 198,405
Commercial Real Estate [Member]
Financing Receivable Modifications [Line Items]
Number of modifications | Modification	83	81	58
Pre- modification recorded investment	$ 44,924	$ 44,870	$ 56,893
Post- modification	40,882	43,737	55,717
Principal Deferral [Member]
Financing Receivable Modifications [Line Items]
Post- modification	62,302	164,883	123,206
Principal Deferral [Member] | Commercial Real Estate [Member]
Financing Receivable Modifications [Line Items]
Post- modification	17,039	23,558	48,388
Other [Member]
Financing Receivable Modifications [Line Items]
Post- modification	7,818	4,676	17,683
Other [Member] | Commercial Real Estate [Member]
Financing Receivable Modifications [Line Items]
Post- modification	868	4,576	4,087
Combination of Concession Types [Member]
Financing Receivable Modifications [Line Items]
Post- modification	121,402	98,856	57,516
Combination of Concession Types [Member] | Commercial Real Estate [Member]
Financing Receivable Modifications [Line Items]
Post- modification	$ 22,975	$ 15,603	$ 3,242
Residential [Member]
Financing Receivable Modifications [Line Items]
Number of modifications | Modification	141	119	85
Pre- modification recorded investment	$ 31,827	$ 20,057	$ 10,485
Post- modification	34,607	21,138	11,072
Residential [Member] | Principal Deferral [Member]
Financing Receivable Modifications [Line Items]
Post- modification	16,633	11,771	6,528
Residential [Member] | Other [Member]
Financing Receivable Modifications [Line Items]
Post- modification			267
Residential [Member] | Combination of Concession Types [Member]
Financing Receivable Modifications [Line Items]
Post- modification	$ 17,974	$ 9,367	$ 4,277
Residential Limited Documentation [Member]
Financing Receivable Modifications [Line Items]
Number of modifications | Modification	20	21	11
Pre- modification recorded investment	$ 4,230	$ 3,560	$ 1,962
Post- modification	4,572	3,964	2,072
Residential Limited Documentation [Member] | Principal Deferral [Member]
Financing Receivable Modifications [Line Items]
Post- modification	911	1,047	437
Residential Limited Documentation [Member] | Combination of Concession Types [Member]
Financing Receivable Modifications [Line Items]
Post- modification	$ 3,661	$ 2,917	$ 1,635
Home Equity Lines and Loans [Member]
Financing Receivable Modifications [Line Items]
Number of modifications | Modification	110	103	71
Pre- modification recorded investment	$ 10,049	$ 11,870	$ 7,378
Post- modification	10,213	11,871	7,379
Home Equity Lines and Loans [Member] | Principal Deferral [Member]
Financing Receivable Modifications [Line Items]
Post- modification	1,137	761	2,175
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	$ 8,585	$ 11,110	$ 5,204
Automobile [Member]
Financing Receivable Modifications [Line Items]
Number of modifications | Modification	69	163	302
Pre- modification recorded investment	$ 1,378	$ 1,264	$ 3,053
Post- modification	1,378	1,264	3,053
Automobile [Member] | Principal Deferral [Member]
Financing Receivable Modifications [Line Items]
Post- modification	1,203	1,124	1,818
Automobile [Member] | Other [Member]
Financing Receivable Modifications [Line Items]
Post- modification		55	287
Automobile [Member] | Combination of Concession Types [Member]
Financing Receivable Modifications [Line Items]
Post- modification	$ 175	$ 85	$ 948
Other [Member]
Financing Receivable Modifications [Line Items]
Number of modifications | Modification	9	79	155
Pre- modification recorded investment	$ 160	$ 1,209	$ 2,507
Post- modification	160	1,209	2,507
Other [Member] | Principal Deferral [Member]
Financing Receivable Modifications [Line Items]
Post- modification	$ 160	968	1,995
Other [Member] | Other [Member]
Financing Receivable Modifications [Line Items]
Post- modification		45	116
Other [Member] | Combination of Concession Types [Member]
Financing Receivable Modifications [Line Items]
Post- modification		$ 196	$ 396
Residential Builder and Developer [Member]
Financing Receivable Modifications [Line Items]
Number of modifications | Modification	3	6	2
Pre- modification recorded investment	$ 12,291	$ 39,660	$ 10,650
Post- modification	10,879	38,081	10,598
Residential Builder and Developer [Member] | Principal Deferral [Member]
Financing Receivable Modifications [Line Items]
Post- modification		22,958	$ 10,598
Residential Builder and Developer [Member] | Combination of Concession Types [Member]
Financing Receivable Modifications [Line Items]
Post- modification	$ 10,879	$ 15,123
Other Commercial Construction [Member]
Financing Receivable Modifications [Line Items]
Number of modifications | Modification	2	3	6
Pre- modification recorded investment	$ 168	$ 3,113	$ 10,743
Post- modification	168	3,032	10,835
Other Commercial Construction [Member] | Principal Deferral [Member]
Financing Receivable Modifications [Line Items]
Post- modification	$ 168	250	460
Other Commercial Construction [Member] | Combination of Concession Types [Member]
Financing Receivable Modifications [Line Items]
Post- modification		$ 2,782	$ 10,375
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable Modifications [Line Items]
Number of modifications | Modification	217	164	127
Pre- modification recorded investment	$ 111,036	$ 154,093	$ 101,129
Post- modification	88,663	144,119	95,172
Commercial, Financial, Leasing, etc. [Member] | Principal Deferral [Member]
Financing Receivable Modifications [Line Items]
Post- modification	25,051	102,446	50,807
Commercial, Financial, Leasing, etc. [Member] | Other [Member]
Financing Receivable Modifications [Line Items]
Post- modification	6,459		12,926
Commercial, Financial, Leasing, etc. [Member] | Combination of Concession Types [Member]
Financing Receivable Modifications [Line Items]
Post- modification	$ 57,153	$ 41,673	$ 31,439