Recent Authoritative Accounting Guidance (Details) - USD ($) $ in Millions	Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total stockholders’ equity	$ 1,956.1		$ 2,013.9	$ 1,736.9	$ 1,693.9
Off-balance sheet credit liability	2.1	$ 0.2	0.0	0.0
Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Off-balance sheet credit liability		2.3		0.0
Accounting Standards Update 2016-13 | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses		30.0
Deferred tax assets		8.2
Retained earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total stockholders’ equity	$ 897.6		$ 953.6	$ 874.7	$ 851.8
Retained earnings | Accounting Standards Update 2016-13 | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total stockholders’ equity		24.1
Off-balance sheet credit liability		$ 2.3