Long-term Debt - 2.25% Convertible Senior Notes (Details) $ / shares in Units, $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2017 USD ($) $ / shares	Dec. 31, 2016 USD ($) $ / shares
Debt Instrument [Line Items]
Carrying value, long-term	$ 241.7	$ 240.0
Unamortized discount and deferred financing costs	$ 3.2	3.4
2 1/4% Notes
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage	2.25%
Debt issuance costs	$ 5.8
Carrying value, long-term	241.7	240.0
Unamortized discount and deferred financing costs	58.3	60.0
Principal amount	300.0	300.0
Carrying amount of equity component, net of equity issuance costs	$ 54.5	$ 54.5
Remaining amortization period (years)	6 years 9 months	7 years
Effective interest rate	5.80%	5.80%
Conversion rate (shares of common stock per $1,000 principal amount)	38.4615	38.4615
Conversion price (in dollars per share of common stock) | $ / shares	$ 26.00	$ 26.00
Interest expense-contractual interest	$ 1.7
Interest expense-amortization of debt discount	1.6
Interest expense-amortization of deferred financing costs	0.0
Debt Component of Convertible Debt | 2 1/4% Notes
Debt Instrument [Line Items]
Debt issuance costs	4.7
Equity Component of Convertible Debt | 2 1/4% Notes
Debt Instrument [Line Items]
Debt issuance costs	$ 1.1