Long-term Debt - Summary of Long-term Debt (Details) - USD ($) $ in Millions	Mar. 31, 2017	Jan. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Total senior debt	$ 383.1		$ 388.0
Total convertible senior notes	241.7		240.0
Total convertible subordinated notes	0.0		35.6
Total debt, net of unamortized discount and deferred financing costs	624.8		663.6
Less: Amounts due within one year	(19.9)		(55.6)
Total long-term debt, net of unamortized discount and deferred financing costs	604.9		608.0
Term loan
Debt Instrument [Line Items]
Total senior debt	385.0		390.0
Unamortized deferred financing costs	$ (1.9)		(2.0)
Effective interest rate	3.23%
2.25% Senior Convertible Notes
Debt Instrument [Line Items]
Principal amount	$ 300.0		300.0
Unamortized deferred financing costs	(58.3)		(60.0)
Total convertible senior notes	$ 241.7		$ 240.0
Effective interest rate	5.80%		5.80%
Debt instrument interest rate stated percentage	2.25%
4.0625% Debentures
Debt Instrument [Line Items]
Total convertible subordinated notes	$ 0.0	$ 35.6	$ 35.6
Debt instrument interest rate stated percentage	4.0625%