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Debt (Details) - USD ($) $ in Millions	Jun. 30, 2020	Jun. 25, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Less transaction costs - 2025 Notes	$ (5.5)		$ 0.0
Discount - 2025 Notes	(38.9)		0.0
Total long-term debt	208.7		154.6
Convertible Senior Notes Due 2025
Debt Instrument [Line Items]
Less transaction costs - 2025 Notes	(6.7)
Discount - 2025 Notes	$ (38.9)
Convertible Debt
Debt Instrument [Line Items]
Debt interest rate	4.125%
Long-term debt, gross	$ 225.0		0.0
Convertible Debt \| Convertible Senior Notes Due 2025
Debt Instrument [Line Items]
Debt interest rate	4.125%
Less transaction costs - 2025 Notes		$ (1.3)
Discount - 2025 Notes		$ (42.6)
Revolving Credit Facility
Debt Instrument [Line Items]
Letters of credit outstanding amount	$ 11.0		11.0
Available funds	285.9		234.4
Revolving Credit Facility \| Line of Credit
Debt Instrument [Line Items]
Long-term debt, gross	$ 28.1		$ 154.6
LIBOR borrowings \| Revolving Credit Facility
Debt Instrument [Line Items]
Interest Rate Percentage	3.00%
Base rate borrowings \| Revolving Credit Facility
Debt Instrument [Line Items]
Interest Rate Percentage	4.30%