Loans (Unallocated Portion of Allowance for Loan Losses) (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	$ 99,542	$ 92,438	$ 104,453	$ 110,147
Historical Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	59,604	53,738
Specific Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	1,680	6,926
Environmental Risk Adjustment [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	13,477	11,806
Distressed Industries [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	3,093	8,196
Excessive Industry Concentrations [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	2,492	1,866
Large Relationship Concentrations [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	3,807	2,610
Highly-Leveraged Credit Relationships [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	5,305	5,154
Policy Exceptions [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	2,782	2,492
Credit and Collateral Exceptions [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	2,164	1,398
Loans Not Reviewed by Concurrence [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	7,906	7,524
Adjustment for Recoveries [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	(15,837)	(12,200)
General Macroeconomic Risk [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	13,069	2,928
Commercial and Industrial [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	59,192	52,790	54,164	42,774
Commercial and Industrial [Member] | Historical Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	32,421	29,357
Commercial and Industrial [Member] | Specific Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	1,613	4,140
Commercial and Industrial [Member] | Environmental Risk Adjustment [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	6,773	5,497
Commercial and Industrial [Member] | Distressed Industries [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	3,090	7,812
Commercial and Industrial [Member] | Excessive Industry Concentrations [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	2,114	1,499
Commercial and Industrial [Member] | Large Relationship Concentrations [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	2,248	1,529
Commercial and Industrial [Member] | Highly-Leveraged Credit Relationships [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	3,958	4,535
Commercial and Industrial [Member] | Policy Exceptions [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	1,907	0
Commercial and Industrial [Member] | Credit and Collateral Exceptions [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	1,483	0
Commercial and Industrial [Member] | Loans Not Reviewed by Concurrence [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	2,110	2,009
Commercial and Industrial [Member] | Adjustment for Recoveries [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	(6,234)	(3,588)
Commercial and Industrial [Member] | General Macroeconomic Risk [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	7,709	0
Commercial Real Estate [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	27,163	22,590	29,346	20,912
Commercial Real Estate [Member] | Historical Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	14,684	13,042
Commercial Real Estate [Member] | Specific Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	67	2,786
Commercial Real Estate [Member] | Environmental Risk Adjustment [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	3,547	3,314
Commercial Real Estate [Member] | Distressed Industries [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	3	384
Commercial Real Estate [Member] | Excessive Industry Concentrations [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	378	367
Commercial Real Estate [Member] | Large Relationship Concentrations [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	1,559	1,081
Commercial Real Estate [Member] | Highly-Leveraged Credit Relationships [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	1,347	619
Commercial Real Estate [Member] | Policy Exceptions [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	875	0
Commercial Real Estate [Member] | Credit and Collateral Exceptions [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	681	0
Commercial Real Estate [Member] | Loans Not Reviewed by Concurrence [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	2,284	2,201
Commercial Real Estate [Member] | Adjustment for Recoveries [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	(1,800)	(1,204)
Commercial Real Estate [Member] | General Macroeconomic Risk [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	3,538	0
Consumer Real Estate [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	5,178	5,230	5,252	3,540
Consumer Real Estate [Member] | Historical Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	2,017	2,644
Consumer Real Estate [Member] | Environmental Risk Adjustment [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	474	664
Consumer Real Estate [Member] | Loans Not Reviewed by Concurrence [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	2,336	2,250
Consumer Real Estate [Member] | Adjustment for Recoveries [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	(364)	(328)
Consumer Real Estate [Member] | General Macroeconomic Risk [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	715	0
Consumer and Other [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	8,009	5,010	3,507	12,635
Consumer and Other [Member] | Historical Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	10,482	8,695
Consumer and Other [Member] | Environmental Risk Adjustment [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	2,683	2,331
Consumer and Other [Member] | Loans Not Reviewed by Concurrence [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	1,176	1,064
Consumer and Other [Member] | Adjustment for Recoveries [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	(7,439)	(7,080)
Consumer and Other [Member] | General Macroeconomic Risk [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	1,107	0
Unallocated [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	0	6,818	12,184	30,286
Unallocated [Member] | Policy Exceptions [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	0	2,492
Unallocated [Member] | Credit and Collateral Exceptions [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	0	1,398
Unallocated [Member] | General Macroeconomic Risk [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	$ 0	$ 2,928