Loans, Leases and Allowance for Credit Losses - Summary of Recorded Investment in Nonaccrual Loans and Loans Past Due 90 Days Still Accruing Interest by Loan Class (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual with No Allowance for Credit Loss	$ 38.9	$ 104.9
Nonaccrual with an Allowance for Credit Loss	33.7	10.3
Total Nonaccrual	72.6	115.2
Loans Past Due 90 Days or More and Still Accruing	0.0	0.0
Loans and Leases Receivable, Impaired, Interest Lost on Nonaccrual Loans	5.3	5.0	$ 2.2
Financing Receivable, Held-for-Sale	5,635.1	0.0
Loans and Leases Receivable, Net of Deferred Income	39,075.4	27,053.0
Tech & Innovation [Member]
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual with No Allowance for Credit Loss	2.1	9.6
Nonaccrual with an Allowance for Credit Loss	11.2	3.9
Total Nonaccrual	13.3	13.5
Loans Past Due 90 Days or More and Still Accruing	0.0	0.0
Loans and Leases Receivable, Net of Deferred Income	1,417.8	1,403.0
Other commercial and industrial [Member]
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual with No Allowance for Credit Loss	12.7	10.9
Nonaccrual with an Allowance for Credit Loss	3.4	6.3
Total Nonaccrual	16.1	17.2
Loans Past Due 90 Days or More and Still Accruing	0.0	0.0
Loans and Leases Receivable, Net of Deferred Income	6,465.7	5,911.2
Commercial Real Estate Owner Occupied [Member]
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual with No Allowance for Credit Loss	11.6	34.5
Nonaccrual with an Allowance for Credit Loss	1.4	0.0
Total Nonaccrual	13.0	34.5
Loans Past Due 90 Days or More and Still Accruing	0.0	0.0
Loans and Leases Receivable, Net of Deferred Income	1,723.7	1,909.3
Hotel franchise finance [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Net of Deferred Income	2,534.0	1,983.9
Other Commercial Real Estate Non owner Occupied [Member]
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual with No Allowance for Credit Loss	11.3	36.5
Nonaccrual with an Allowance for Credit Loss	1.8	0.0
Total Nonaccrual	13.1	36.5
Loans Past Due 90 Days or More and Still Accruing	0.0	0.0
Loans and Leases Receivable, Net of Deferred Income	3,951.8	3,640.2
Residential Real Estate [Member]
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual with No Allowance for Credit Loss	0.0	11.4
Nonaccrual with an Allowance for Credit Loss	15.1	0.0
Total Nonaccrual	15.1	11.4
Loans Past Due 90 Days or More and Still Accruing	0.0	0.0
Loans and Leases Receivable, Net of Deferred Income	9,242.8	2,378.5
Construction and land development [Member]
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual with No Allowance for Credit Loss	1.0
Nonaccrual with an Allowance for Credit Loss	0.0
Total Nonaccrual	1.0
Loans Past Due 90 Days or More and Still Accruing	0.0
Loans and Leases Receivable, Net of Deferred Income	3,005.8	2,429.4
Warehouse lending [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Net of Deferred Income	5,155.9	4,340.2
Municipal and nonprofit [Member]
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual with No Allowance for Credit Loss		1.9
Nonaccrual with an Allowance for Credit Loss		0.0
Total Nonaccrual		1.9
Loans Past Due 90 Days or More and Still Accruing		0.0
Loans and Leases Receivable, Net of Deferred Income	1,579.2	1,728.8
Other, loan segment [Member]
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual with No Allowance for Credit Loss	0.2	0.1
Nonaccrual with an Allowance for Credit Loss	0.2	0.1
Total Nonaccrual	0.4	0.2
Loans Past Due 90 Days or More and Still Accruing	0.0	0.0
Loans and Leases Receivable, Net of Deferred Income	168.9	183.2
Construction And Land Development Land [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Net of Deferred Income	3,005.8	2,429.4
Equity fund resources
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual with No Allowance for Credit Loss	0.0
Nonaccrual with an Allowance for Credit Loss	0.6
Total Nonaccrual	0.6
Loans Past Due 90 Days or More and Still Accruing	0.0
Loans and Leases Receivable, Net of Deferred Income	3,829.8	1,145.3
Financial Asset, Not Past Due
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	39,022.9	27,041.8
Financial Asset, Not Past Due | Tech & Innovation [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	1,417.8	1,403.0
Financial Asset, Not Past Due | Other commercial and industrial [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	6,465.7	5,911.0
Financial Asset, Not Past Due | Commercial Real Estate Owner Occupied [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	1,723.7	1,909.3
Financial Asset, Not Past Due | Hotel franchise finance [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	2,534.0	1,983.9
Financial Asset, Not Past Due | Other Commercial Real Estate Non owner Occupied [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	3,951.8	3,640.2
Financial Asset, Not Past Due | Residential Real Estate [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	9,190.4	2,368.0
Financial Asset, Not Past Due | Construction and land development [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	3,005.8	2,429.4
Financial Asset, Not Past Due | Warehouse lending [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	5,155.9	4,340.2
Financial Asset, Not Past Due | Municipal and nonprofit [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	1,579.2	1,728.8
Financial Asset, Not Past Due | Other, loan segment [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	168.8	182.7
Financial Asset, Not Past Due | Equity fund resources
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	3,829.8	1,145.3
Financial Asset, 30 to 59 Days Past Due [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	50.8	9.7
Financial Asset, 30 to 59 Days Past Due [Member] | Tech & Innovation [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	0.0	0.0
Financial Asset, 30 to 59 Days Past Due [Member] | Other commercial and industrial [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	0.0	0.2
Financial Asset, 30 to 59 Days Past Due [Member] | Commercial Real Estate Owner Occupied [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	0.0	0.0
Financial Asset, 30 to 59 Days Past Due [Member] | Hotel franchise finance [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	0.0	0.0
Financial Asset, 30 to 59 Days Past Due [Member] | Other Commercial Real Estate Non owner Occupied [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	0.0	0.0
Financial Asset, 30 to 59 Days Past Due [Member] | Residential Real Estate [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	50.7	9.1
Financial Asset, 30 to 59 Days Past Due [Member] | Construction and land development [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	0.0	0.0
Financial Asset, 30 to 59 Days Past Due [Member] | Warehouse lending [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	0.0	0.0
Financial Asset, 30 to 59 Days Past Due [Member] | Municipal and nonprofit [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	0.0	0.0
Financial Asset, 30 to 59 Days Past Due [Member] | Other, loan segment [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	0.1	0.4
Financial Asset, 30 to 59 Days Past Due [Member] | Equity fund resources
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	0.0	0.0
Financial Asset, 60 to 89 Days Past Due [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	1.7	1.5
Financial Asset, 60 to 89 Days Past Due [Member] | Tech & Innovation [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	0.0	0.0
Financial Asset, 60 to 89 Days Past Due [Member] | Other commercial and industrial [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	0.0	0.0
Financial Asset, 60 to 89 Days Past Due [Member] | Commercial Real Estate Owner Occupied [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	0.0	0.0
Financial Asset, 60 to 89 Days Past Due [Member] | Hotel franchise finance [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	0.0	0.0
Financial Asset, 60 to 89 Days Past Due [Member] | Other Commercial Real Estate Non owner Occupied [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	0.0	0.0
Financial Asset, 60 to 89 Days Past Due [Member] | Residential Real Estate [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	1.7	1.4
Financial Asset, 60 to 89 Days Past Due [Member] | Construction and land development [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	0.0	0.0
Financial Asset, 60 to 89 Days Past Due [Member] | Warehouse lending [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	0.0	0.0
Financial Asset, 60 to 89 Days Past Due [Member] | Municipal and nonprofit [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	0.0	0.0
Financial Asset, 60 to 89 Days Past Due [Member] | Other, loan segment [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	0.0	0.1
Financial Asset, 60 to 89 Days Past Due [Member] | Equity fund resources
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	0.0	0.0
Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans Past Due 90 Days or More and Still Accruing	0.0	0.0
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Tech & Innovation [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans Past Due 90 Days or More and Still Accruing	0.0	0.0
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Other commercial and industrial [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans Past Due 90 Days or More and Still Accruing	0.0	0.0
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Commercial Real Estate Owner Occupied [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans Past Due 90 Days or More and Still Accruing	0.0	0.0
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Hotel franchise finance [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans Past Due 90 Days or More and Still Accruing	0.0	0.0
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Other Commercial Real Estate Non owner Occupied [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans Past Due 90 Days or More and Still Accruing	0.0	0.0
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Residential Real Estate [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans Past Due 90 Days or More and Still Accruing	0.0	0.0
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Construction and land development [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans Past Due 90 Days or More and Still Accruing	0.0	0.0
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Warehouse lending [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans Past Due 90 Days or More and Still Accruing	0.0	0.0
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Municipal and nonprofit [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans Past Due 90 Days or More and Still Accruing	0.0	0.0
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Other, loan segment [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans Past Due 90 Days or More and Still Accruing	0.0	0.0
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Equity fund resources
Financing Receivable, Nonaccrual [Line Items]
Loans Past Due 90 Days or More and Still Accruing	0.0	0.0
Financial Asset, Past Due
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	52.5	11.2
Financial Asset, Past Due | Tech & Innovation [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	0.0	0.0
Financial Asset, Past Due | Other commercial and industrial [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	0.0	0.2
Financial Asset, Past Due | Commercial Real Estate Owner Occupied [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	0.0	0.0
Financial Asset, Past Due | Hotel franchise finance [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	0.0	0.0
Financial Asset, Past Due | Other Commercial Real Estate Non owner Occupied [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	0.0	0.0
Financial Asset, Past Due | Residential Real Estate [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	52.4	10.5
Financial Asset, Past Due | Construction and land development [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	0.0	0.0
Financial Asset, Past Due | Warehouse lending [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	0.0	0.0
Financial Asset, Past Due | Municipal and nonprofit [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	0.0	0.0
Financial Asset, Past Due | Other, loan segment [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	0.1	0.5
Financial Asset, Past Due | Equity fund resources
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Gross	$ 0.0	$ 0.0