Fair Value Accounting - Fair Value of Assets and Liabilities (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Hedged Asset, Fair Value Hedge, Cumulative Increase (Decrease)	$ 38,500,000	$ 85,500,000
Hedged Liability, Fair Value Hedge, Cumulative Increase (Decrease)	0	(2,700,000)
Investment securities - equity	158,500,000	167,300,000
Subordinated Debt Obligations, Fair Value Disclosure	67,400,000	65,900,000
Debt Securities, Available-for-sale	6,188,800,000	4,708,500,000
Servicing Asset at Fair Value, Amount	698,000,000.0	0
Debt Securities, Available-for-sale, Amortized Cost	6,166,500,000	4,586,400,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	103,600,000	137,600,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	(81,300,000)	(15,500,000)
Other Security Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	81,700,000	55,900,000
Debt Securities, Available-for-sale, Amortized Cost	75,300,000	54,100,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	11,000,000.0	7,300,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	(4,600,000)	(5,500,000)
Collateralized Loan Obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	926,200,000	146,900,000
Debt Securities, Available-for-sale, Amortized Cost	926,000,000.0	146,900,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	500,000	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	(300,000)	0
Commercial Mortgage Backed Securities Issued By US Government Sponsored Enterprise [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	68,500,000	84,600,000
Debt Securities, Available-for-sale, Amortized Cost	68,200,000	80,800,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	900,000	3,800,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	(600,000)	0
Corporate debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	382,900,000	270,200,000
Debt Securities, Available-for-sale, Amortized Cost	382,700,000	271,100,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	9,200,000	4,800,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	(9,000,000.0)	(5,700,000)
Private label residential mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	1,508,000,000	1,476,900,000
Debt Securities, Available-for-sale, Amortized Cost	1,528,700,000	1,461,700,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	3,500,000	15,700,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	(24,200,000)	(500,000)
Residential mortgage-backed securities issued by GSEs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	1,993,400,000	1,486,600,000
Debt Securities, Available-for-sale, Amortized Cost	2,027,500,000	1,462,500,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	7,300,000	27,900,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	(41,400,000)	(3,800,000)
Nontaxable Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	1,215,100,000	1,187,400,000
Debt Securities, Available-for-sale, Amortized Cost	1,145,100,000	1,109,300,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	71,200,000	78,100,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	(1,200,000)	0
US Treasury Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	13,000,000.0
Debt Securities, Available-for-sale, Amortized Cost	13,000,000.0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0
Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities - equity	158,500,000	167,300,000
Loans Held-for-sale, Fair Value Disclosure	3,939,700,000
Derivative Liability	99,800,000	87,500,000
Derivative Asset	50,200,000	4,200,000
Debt Securities, Available-for-sale	6,188,800,000	4,708,500,000
Servicing Asset at Fair Value, Amount	698,000,000.0
Fair Value, Recurring [Member] | Other Security Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	81,700,000	55,900,000
Fair Value, Recurring [Member] | Collateralized Loan Obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	926,200,000	146,900,000
Fair Value, Recurring [Member] | Commercial Mortgage Backed Securities Issued By US Government Sponsored Enterprise [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	68,500,000	84,600,000
Fair Value, Recurring [Member] | Corporate debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	382,900,000	270,200,000
Fair Value, Recurring [Member] | Private label residential mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	1,508,000,000	1,476,900,000
Fair Value, Recurring [Member] | Residential mortgage-backed securities issued by GSEs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	1,993,400,000	1,486,600,000
Fair Value, Recurring [Member] | Nontaxable Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	1,215,100,000	1,187,400,000
Fair Value, Recurring [Member] | US Treasury Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	13,000,000.0
Fair Value, Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities - equity	141,300,000	141,700,000
Loans Held-for-sale, Fair Value Disclosure	0
Derivative Liability	0	0
Derivative Asset	0	0
Subordinated Debt Obligations, Fair Value Disclosure	0	0
Debt Securities, Available-for-sale	40,400,000	26,500,000
Servicing Asset at Fair Value, Amount	0
Fair Value, Recurring [Member] | Level 1 [Member] | Other Security Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	27,400,000	26,500,000
Fair Value, Recurring [Member] | Level 1 [Member] | Collateralized Loan Obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Level 1 [Member] | Commercial Mortgage Backed Securities Issued By US Government Sponsored Enterprise [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Level 1 [Member] | Corporate debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Level 1 [Member] | Private label residential mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Level 1 [Member] | Residential mortgage-backed securities issued by GSEs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Level 1 [Member] | Nontaxable Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Level 1 [Member] | US Treasury Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	13,000,000.0
Fair Value, Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities - equity	17,200,000	25,600,000
Loans Held-for-sale, Fair Value Disclosure	3,894,200,000
Derivative Liability	98,200,000	87,500,000
Derivative Asset	39,200,000	4,200,000
Subordinated Debt Obligations, Fair Value Disclosure	0	0
Debt Securities, Available-for-sale	6,148,400,000	4,682,000,000
Servicing Asset at Fair Value, Amount	0
Fair Value, Recurring [Member] | Level 2 [Member] | Other Security Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	54,300,000	29,400,000
Fair Value, Recurring [Member] | Level 2 [Member] | Collateralized Loan Obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	926,200,000	146,900,000
Fair Value, Recurring [Member] | Level 2 [Member] | Commercial Mortgage Backed Securities Issued By US Government Sponsored Enterprise [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	68,500,000	84,600,000
Fair Value, Recurring [Member] | Level 2 [Member] | Corporate debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	382,900,000	270,200,000
Fair Value, Recurring [Member] | Level 2 [Member] | Private label residential mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	1,508,000,000	1,476,900,000
Fair Value, Recurring [Member] | Level 2 [Member] | Residential mortgage-backed securities issued by GSEs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	1,993,400,000	1,486,600,000
Fair Value, Recurring [Member] | Level 2 [Member] | Nontaxable Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	1,215,100,000	1,187,400,000
Fair Value, Recurring [Member] | Level 2 [Member] | US Treasury Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	0
Fair Value, Recurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities - equity	0	0
Loans Held-for-sale, Fair Value Disclosure	45,500,000
Derivative Liability	1,600,000	0
Derivative Asset	11,000,000.0	0
Subordinated Debt Obligations, Fair Value Disclosure	67,400,000	65,900,000
Debt Securities, Available-for-sale	0	0
Servicing Asset at Fair Value, Amount	698,000,000.0
Fair Value, Recurring [Member] | Level 3 [Member] | Other Security Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Level 3 [Member] | Collateralized Loan Obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Level 3 [Member] | Commercial Mortgage Backed Securities Issued By US Government Sponsored Enterprise [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Level 3 [Member] | Corporate debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Level 3 [Member] | Private label residential mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Level 3 [Member] | Residential mortgage-backed securities issued by GSEs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Level 3 [Member] | Nontaxable Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Level 3 [Member] | US Treasury Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	0
Fair Value, Recurring [Member] | CRA investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities - equity	44,600,000	53,400,000
Fair Value, Recurring [Member] | CRA investments [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities - equity	27,400,000	27,800,000
Fair Value, Recurring [Member] | CRA investments [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities - equity	17,200,000	25,600,000
Fair Value, Recurring [Member] | CRA investments [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities - equity	0	0
Fair Value, Recurring [Member] | Preferred Stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities - equity	113,900,000	113,900,000
Fair Value, Recurring [Member] | Preferred Stock [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities - equity	113,900,000	113,900,000
Fair Value, Recurring [Member] | Preferred Stock [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities - equity	0	0
Fair Value, Recurring [Member] | Preferred Stock [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities - equity	0	0
Junior Subordinated Debt [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Subordinated Debt Obligations, Fair Value Disclosure	$ 67,400,000	$ 65,900,000
Junior subordinated debt, Significant Unobservable Inputs	Implied credit rating of the Company	Implied credit rating of the Company
Valuation Technique, Discounted Cash Flow [Member] | Junior Subordinated Debt [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Junior subordinated debt, Significant Unobservable Inputs	Discounted cash flow	Discounted cash flow