Other Comprehensive Income/Loss - Schedule of Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Investment securities available-for sale:
Change in net unrealized gain during period, pre-tax	$ 2.5	$ (57.5)	$ (23.9)	$ 20.7
Change in net unrealized gain during period, tax expense (benefit)	(0.7)	14.4	5.9	(5.2)
OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, after Tax	1.8	(43.1)	(18.0)	15.5
Reclassification adjustment for net gains included in income, pre-tax	0.0	0.1	0.0	23.5
Reclassification adjustment for net gains included in income, tax expense (benefit)	0.0	0.0	0.0	(5.8)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0.0	0.1	0.0	17.7
OCI, Debt Securities, Available-for-Sale, Transfer from Held-to-Maturity, Gain (Loss), before Adjustment, after Tax			0.0	(5.4)
OCI, Debt Securities, Available-for-Sale, Transfer from Held-to-Maturity, Gain (Loss), before Adjustment, Tax			0.0	1.8
OCI, Debt Securities, Available-for-Sale, Transfer to Held-to-Maturity, Adjustment from AOCI for Amortization of Gain (Loss), after Tax	(0.1)	(0.3)	(0.3)	(0.6)
Unrealized loss on derivatives, tax expense (benefit)	(1.2)	(0.4)	(2.1)	(0.5)
Unrealized loss on derivatives, net of tax	(3.7)	(17.7)	(16.7)	(10.6)
Other comprehensive income (loss), before tax	1.9	(79.9)	(38.6)	24.1
Other Comprehensive Income (Loss), tax expense (benefit)	(0.5)	20.0	9.6	(6.0)
Other Comprehensive Income (Loss), Net of Tax	1.4	(59.9)	(29.0)	18.1
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification and Tax	(5.1)	(23.6)	(22.5)	(14.1)
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, before Tax	4.6	1.5	8.1	2.0
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax	3.4	1.1	6.0	1.5
Total stockholders’ equity	3,225.3	3,121.2	3,225.3	3,121.2	$ 3,209.7	$ 3,227.5	$ 3,160.3	$ 3,073.8
Reclassification adjustment for securities transferred from held-to-maturity to available-for-sale	0.0	0.0	0.0	(7.2)
OCI, Debt Securities, Available-for-Sale, Transfer to Held-to-Maturity, Adjustment from AOCI for Amortization of Gain (Loss), before Tax	(0.1)	(0.4)	(0.3)	(0.8)
Amortization of unrealized gains on available-for-sale securities transferred into held-to-maturity, tax expense (benefit)	0.0	0.1	0.0	0.2
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification, Tax	$ 1.4	$ 5.9	$ 5.8	$ 3.5