Derivative Financial Instruments and Hedging Activities - Schedule of Notional Amount and Fair Value (Detail) - USD ($)	Mar. 31, 2020	Dec. 31, 2019
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gross Amount Recognized	$ 36,100,000	$ 18,400,000
Gross Amounts Recognized	945,700,000	341,000,000.0
Financial liabilities	197,300,000	81,600,000
Financial liabilities	198,500,000	96,200,000
Forward commitments to sell residential mortgage loans
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gross Amount Recognized	600,000	500,000
Interest rate-lock commitments on residential mortgage loans
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Financial liabilities	700,000	500,000
Derivatives Not Designated as Hedging Instruments
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gross Amounts Recognized	945,700,000	341,000,000.0
Financial liabilities	198,500,000	96,200,000
Derivatives Not Designated as Hedging Instruments \| Forward commitments to sell residential mortgage loans
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	77,700,000	23,300,000
Gross Amounts Recognized	600,000	500,000
Financial liabilities	0	0
Derivatives Not Designated as Hedging Instruments \| Interest rate-lock commitments on residential mortgage loans
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	53,800,000	33,600,000
Gross Amounts Recognized	0	0
Financial liabilities	700,000	500,000
Derivatives Designated as Hedging Instruments
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gross Amounts Recognized	0	0
Financial liabilities	0	0
Interest rate swaps \| Derivatives Not Designated as Hedging Instruments \| Commercial customers
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	9,207,600,000	8,847,700,000
Gross Amounts Recognized	905,400,000	320,500,000
Financial liabilities	0	13,900,000
Interest rate swaps \| Derivatives Not Designated as Hedging Instruments \| Institutional counterparties
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	9,211,400,000	8,851,800,000
Gross Amount Recognized	27,500,000	17,100,000
Financial liabilities	184,500,000	78,200,000
Interest rate swaps \| Derivatives Designated as Hedging Instruments \| Cash flow \| FHLB advances
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	550,000,000	0
Gross Amounts Recognized	0	0
Financial liabilities	0	0
Interest rate swaps \| Derivatives Designated as Hedging Instruments \| Cash flow \| Loans
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	210,000,000.0	210,000,000.0
Gross Amounts Recognized	0	0
Financial liabilities	0	0
Interest rate swaps \| Derivatives Designated as Hedging Instruments \| Subordinated notes \| Fair value
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	375,000,000.0	375,000,000.0
Gross Amounts Recognized	0	0
Financial liabilities	0	0
Interest rate caps \| Derivatives Not Designated as Hedging Instruments \| Commercial customers
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	253,400,000	246,000,000.0
Gross Amounts Recognized	3,600,000	1,600,000
Financial liabilities	0	100,000
Interest rate caps \| Derivatives Not Designated as Hedging Instruments \| Institutional counterparties
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	253,400,000	246,000,000.0
Gross Amount Recognized	0	100,000
Financial liabilities	3,600,000	1,600,000
Risk Participation Agreements \| Derivatives Not Designated as Hedging Instruments
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	910,300,000	882,800,000
Gross Amounts Recognized	0	0
Financial liabilities	500,000	100,000
Foreign exchange contracts
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gross Amount Recognized	8,600,000	1,200,000
Financial liabilities	9,200,000	1,800,000
Foreign exchange contracts \| Derivatives Not Designated as Hedging Instruments
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	237,700,000	180,400,000
Gross Amount Recognized	8,600,000	1,200,000
Financial liabilities	$ 9,200,000	$ 1,800,000

Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and elected not to be offset.

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Fair value of financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, not subject to a master netting arrangement.

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