Loans (Unallocated Portion of Allowance for Loan Losses) (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	$ 132,167	$ 132,132	$ 155,364	$ 153,045
Historical Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	69,087	65,398
Specific Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	28,483	16,235
General Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	19,732	22,100
Macroeconomic Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	14,865	28,399
Commercial Portfolio Segment [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	51,593	48,580	59,614	52,915
Commercial Portfolio Segment [Member] | Historical Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	29,015	25,351
Commercial Portfolio Segment [Member] | Specific Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	7,849	2,558
Commercial Portfolio Segment [Member] | General Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	9,840	10,062
Commercial Portfolio Segment [Member] | Macroeconomic Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	4,889	10,609
Commercial And Industrial Energy Financing Receivable [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	37,382	29,052	51,528	60,653
Commercial And Industrial Energy Financing Receivable [Member] | Historical Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	7,873	9,697
Commercial And Industrial Energy Financing Receivable [Member] | Specific Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	20,246	9,671
Commercial And Industrial Energy Financing Receivable [Member] | General Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	5,196	6,014
Commercial And Industrial Energy Financing Receivable [Member] | Macroeconomic Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	4,067	3,670
Commercial Real Estate Portfolio Segment [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	31,037	38,777	30,948	30,213
Commercial Real Estate Portfolio Segment [Member] | Historical Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	21,947	20,817
Commercial Real Estate Portfolio Segment [Member] | Specific Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	383	2,599
Commercial Real Estate Portfolio Segment [Member] | General Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	4,201	4,366
Commercial Real Estate Portfolio Segment [Member] | Macroeconomic Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	4,506	10,995
Total consumer real estate loans [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	4,113	6,103	5,657	4,238
Total consumer real estate loans [Member] | Historical Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	2,690	2,688
Total consumer real estate loans [Member] | Specific Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	0	0
Total consumer real estate loans [Member] | General Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	904	1,671
Total consumer real estate loans [Member] | Macroeconomic Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	519	1,744
Consumer Loan [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	8,042	9,620	$ 7,617	$ 5,026
Consumer Loan [Member] | Historical Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	7,562	6,845
Consumer Loan [Member] | Specific Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	5	1,407
Consumer Loan [Member] | General Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	(409)	(13)
Consumer Loan [Member] | Macroeconomic Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	$ 884	$ 1,381