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Loans, Leases and Allowance for Credit Losses - Schedule of Held for Investment Loan Portfolio Composition of Loans, Leases and Allowance for Credit Losses (Detail) - USD ($) $ in Millions	Jun. 30, 2025	Mar. 31, 2025	Dec. 31, 2024	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans HFI, net of deferred fees and costs	$ 55,939.0		$ 53,676.0
Less: allowance for credit losses	(394.7)	$ (388.6)	(373.8)	$ (351.8)	$ (340.3)	$ (336.7)
Net loans HFI	55,544.0		53,302.0
Warehouse lending
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans HFI, net of deferred fees and costs	8,574.0		8,207.0
Less: allowance for credit losses	(5.9)	(6.3)	(6.4)	(6.5)	(7.3)	(5.8)
Municipal & nonprofit
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans HFI, net of deferred fees and costs	1,634.0		1,620.0
Less: allowance for credit losses	(11.3)	(14.8)	(14.7)	(14.0)	(13.9)	(14.7)
Tech & innovation
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans HFI, net of deferred fees and costs	3,609.0		3,383.0
Less: allowance for credit losses	(45.7)	(44.9)	(55.9)	(45.0)	(48.0)	(42.1)
Equity fund resources
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans HFI, net of deferred fees and costs	857.0		884.0
Less: allowance for credit losses	(2.2)	(1.4)	(1.6)	(1.7)	(1.2)	(1.3)
Other commercial and industrial
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans HFI, net of deferred fees and costs	10,474.0		9,175.0
Less: allowance for credit losses	(109.2)	(91.7)	(77.8)	(84.3)	(67.1)	(81.4)
CRE - owner occupied
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans HFI, net of deferred fees and costs	1,598.0		1,675.0
Less: allowance for credit losses	(3.9)	(3.7)	(3.4)	(5.0)	(6.2)	(6.0)
Hotel franchise finance
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans HFI, net of deferred fees and costs	3,929.0		3,815.0
Less: allowance for credit losses	(36.0)	(33.2)	(35.3)	(39.6)	(35.8)	(33.4)
Other CRE - non-owner occupied
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans HFI, net of deferred fees and costs	6,552.0		6,342.0
Less: allowance for credit losses	(125.0)	(138.1)	(134.4)	(104.5)	(104.7)	(96.0)
Residential
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans HFI, net of deferred fees and costs	13,166.0		12,961.0
Less: allowance for credit losses	(19.9)	(19.7)	(19.7)	(18.8)	(22.1)	(23.1)
Residential EBO
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans HFI, net of deferred fees and costs	929.0		972.0
Less: allowance for credit losses	0.0	0.0	0.0	0.0	0.0	0.0
Construction and land development
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans HFI, net of deferred fees and costs	4,478.0		4,468.0
Less: allowance for credit losses	(33.6)	(32.0)	(21.3)	(29.9)	(31.9)	(30.4)
Other
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans HFI, net of deferred fees and costs	139.0		174.0
Less: allowance for credit losses	$ (2.0)	$ (2.8)	$ (3.3)	$ (2.5)	$ (2.1)	$ (2.5)