Loans - Allowance for Credit Losses By Loan Class Accordance With Methodology Used Prior to CECL (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Loans and Leases Receivable, Allowance	$ 250,061	$ 132,167
Historical Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Loans and Leases Receivable, Allowance		69,087
Specific Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Loans and Leases Receivable, Allowance	15,672	28,483
General Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Loans and Leases Receivable, Allowance		19,732
Macroeconomic Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Loans and Leases Receivable, Allowance		14,865
Commercial Portfolio Segment [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Loans and Leases Receivable, Allowance	98,536	51,593
Commercial Portfolio Segment [Member] | Historical Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Loans and Leases Receivable, Allowance		29,015
Commercial Portfolio Segment [Member] | Specific Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Loans and Leases Receivable, Allowance	12,090	7,849
Commercial Portfolio Segment [Member] | General Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Loans and Leases Receivable, Allowance		9,840
Commercial Portfolio Segment [Member] | Macroeconomic Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Loans and Leases Receivable, Allowance		4,889
Commercial and Industrial Total Energy Loans [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Loans and Leases Receivable, Allowance	40,817	37,382
Commercial and Industrial Total Energy Loans [Member] | Historical Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Loans and Leases Receivable, Allowance		7,873
Commercial and Industrial Total Energy Loans [Member] | Specific Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Loans and Leases Receivable, Allowance	2,250	20,246
Commercial and Industrial Total Energy Loans [Member] | General Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Loans and Leases Receivable, Allowance		5,196
Commercial and Industrial Total Energy Loans [Member] | Macroeconomic Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Loans and Leases Receivable, Allowance		4,067
Commercial Real Estate Portfolio Segment [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Loans and Leases Receivable, Allowance	93,425	31,037
Commercial Real Estate Portfolio Segment [Member] | Historical Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Loans and Leases Receivable, Allowance		21,947
Commercial Real Estate Portfolio Segment [Member] | Specific Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Loans and Leases Receivable, Allowance	1,314	383
Commercial Real Estate Portfolio Segment [Member] | General Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Loans and Leases Receivable, Allowance		4,201
Commercial Real Estate Portfolio Segment [Member] | Macroeconomic Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Loans and Leases Receivable, Allowance		4,506
Total consumer real estate loans [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Loans and Leases Receivable, Allowance	8,998	4,113
Total consumer real estate loans [Member] | Historical Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Loans and Leases Receivable, Allowance		2,690
Total consumer real estate loans [Member] | Specific Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Loans and Leases Receivable, Allowance	0	0
Total consumer real estate loans [Member] | General Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Loans and Leases Receivable, Allowance		904
Total consumer real estate loans [Member] | Macroeconomic Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Loans and Leases Receivable, Allowance		519
Consumer Loan [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Loans and Leases Receivable, Allowance	8,285	8,042
Consumer Loan [Member] | Historical Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Loans and Leases Receivable, Allowance		7,562
Consumer Loan [Member] | Specific Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Loans and Leases Receivable, Allowance	$ 18	5
Consumer Loan [Member] | General Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Loans and Leases Receivable, Allowance		(409)
Consumer Loan [Member] | Macroeconomic Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Loans and Leases Receivable, Allowance		$ 884