Consolidated Balance Sheets - USD ($) $ in Millions	Jun. 30, 2026	Dec. 31, 2025
Assets [Abstract]
Cash and due from banks	$ 344.2	$ 358.2
Interest bearing deposits in banks	822.8	951.4
Federal funds sold	0.1	0.1
Total cash and cash equivalents	1,167.1	1,309.7
Investment securities:
Available-for-sale, at fair value	5,769.8	5,288.1
Held-to-maturity (estimated fair values of $2,000.3 at June 30, 2026 and $2,136.6 at December 31, 2025)	2,215.8	2,342.1
Total investment securities	7,985.6	7,630.2
Federal Home Loan Bank Stock and Federal Reserve Bank Stock	106.3	106.3
Loans held for sale ($2.1 and $1.1 of which is recorded at fair value at June 30, 2026 and December 31, 2025, respectively)	2.1	73.6
Allowance for credit losses	(182.2)	(191.4)
Net loans held for investment	14,099.2	15,010.2
Goodwill	1,100.9	1,100.9
Bank Owned Life Insurance	528.1	523.0
Premises and equipment, net of accumulated depreciation	412.8	406.6
Other intangibles, net of accumulated amortization	46.7	53.3
Accrued interest receivable	97.3	102.6
Mortgage servicing rights, net of accumulated amortization	22.0	23.1
Real Estate Acquired Through Foreclosure	5.3	3.4
Deferred tax assets	57.6	59.6
Other assets	254.0	238.1
Total assets	25,885.0	26,640.6
Deposits:
Noninterest bearing	5,312.0	5,286.8
Interest bearing	16,129.3	16,801.5
Total deposits	21,441.3	22,088.3
Securities sold under repurchase agreements	455.2	479.6
Accounts payable and accrued expenses	334.6	286.8
Accrued interest payable	27.7	36.9
Long-term debt	146.8	146.3
Allowance for credit losses on off-balance sheet credit exposures	6.9	5.9
Subordinated debentures held by subsidiary trusts	149.9	149.8
Total liabilities	$ 22,562.4	$ 23,193.6
Preferred Stock, Shares Authorized	100,000
Preferred Stock, Par or Stated Value Per Share	$ 0.00001	$ 0.00001
Common Stock, Shares, Issued	95,548,084	101,105,745
Stockholders’ equity:
Preferred stock, $0.00001 par value; 100,000 shares authorized at June 30, 2026 and December 31, 2025; zero issued and outstanding, respectively	$ 0.0	$ 0.0
Common stock and additional paid-in-capital, $0.00001 par value; 150,000,000 shares authorized at June 30, 2026 and December 31, 2025; 95,548,084 and 101,105,745 shares issued and outstanding, respectively	2,199.5	2,350.9
Retained earnings	1,326.6	1,274.2
Accumulated other comprehensive loss, net	(203.5)	(178.1)
Total stockholders’ equity	3,322.6	3,447.0
Total liabilities and stockholders’ equity	$ 25,885.0	$ 26,640.6
Common Stock, Shares Authorized	150,000,000
Shares outstanding (in shares)	95,548,084	101,105,745