Long-Term Debt - 2 1/4% Convertible Senior Notes (Details) $ / shares in Units, $ in Millions	1 Months Ended	12 Months Ended
	Dec. 31, 2015 USD ($)	Dec. 31, 2016 USD ($) $ / shares	Nov. 30, 2015 USD ($)	Nov. 30, 2014 USD ($)
Debt Instrument [Line Items]
Long term debt	$ 639.0	$ 663.6
Deferred financing costs	2.1	3.4
Principal amount of debt	650.6	725.6
Interest expense-amortization of deferred financing costs (less than)	0.2	2.0	$ 2.7	$ 3.6
2.25% Convertible Subordinated Debentures [Member]
Debt Instrument [Line Items]
Long term debt	0.0	240.0
Deferred financing costs	0.0	60.0
Principal amount of debt	$ 0.0	300.0
Carrying amount of equity component, net of equity issuance costs		$ 54.5
Remaining amortization period		7 years
Effective interest rate		5.80%
Common stock conversion rate		38.4615
Conversion price per share (in USD per share) | $ / shares		$ 26.00
Interest expense-contractual interest		$ 0.3
Interest expense-amortization of debt discount		0.3
Interest expense-amortization of deferred financing costs (less than)		$ 0.1