Borrowings (Details) - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Long-term borrowings
Long-term debt	$ 196.1		$ 192.6
Less: current maturities	0.0		0.0
Long-term portion	196.1		192.6
Long-term Debt, Maturities, Repayments of Principal, Remainder of Fiscal Year	0.0
Long-term Debt, Maturities, Repayments of Principal in Year Two	0.0
Long-term Debt, Maturities, Repayments of Principal in Year Three	0.0
Supplemental Cash Flow Information, Interest Paid
Interest Paid, Net	4.1	$ 5.8
Convertible Debt \| Convertible Notes Due Twenty Twenty One
Long-term borrowings
Convertible Notes Payable	145.4		141.9
Long-term Debt, Maturities, Repayments of Principal in Year Four	172.5
Debt Instrument, Unamortized Discount	27.1		30.6
Line of Credit \| Credit Facility due October 11, 2022
Long-term borrowings
Long-term Line of Credit	50.7		$ 50.7
Long-term Debt, Maturities, Repayments of Principal in Year Five	$ 50.7

Including the current and noncurrent portions, carrying value as of the balance sheet date of a written promise to pay a note, initially due after one year or beyond the operating cycle if longer, which can be exchanged for a specified amount of one or more securities (typically common stock), at the option of the issuer or the holder.

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