Summary of Significant Accounting Policies (Cash and Cash Equivalents) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Accounting Policies [Abstract]
Cash and cash equivalents	$ 42.0	$ 53.7	$ 25.2
Restricted Cash, Current	0.0	0.7	0.0
Restricted Cash, Noncurrent	0.0	0.0	1.1
Cash, cash equivalents and restricted cash at beginning of period	$ 42.0	$ 54.4	$ 26.2	$ 36.9