Fair Value Measurements (Narrative) (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Senior Notes | 2017 Senior Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, fair value	$ 458.8	$ 485.0
Convertible Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, fair value	69.3	$ 193.4
Term Loan B
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, fair value	$ 418.6