Long-term Debt - Summary of Long-term Debt (Details) - USD ($)	Jun. 30, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Total senior debt	$ 378,100,000	$ 388,000,000
Total convertible senior notes	243,600,000	240,000,000
Total convertible subordinated notes	0	35,600,000
Total debt, net of unamortized discount and deferred financing costs	621,700,000	663,600,000
Less: Amounts due within one year	(19,900,000)	(55,600,000)
Total long-term debt, net of unamortized discount and deferred financing costs	601,800,000	608,000,000
Term loan
Debt Instrument [Line Items]
Total senior debt	380,000,000	390,000,000
Unamortized discount and deferred financing costs	$ (1,900,000)	(2,000,000)
Effective interest rate	3.48%
2.25% Senior Convertible Notes
Debt Instrument [Line Items]
Principal amount	$ 300,000,000.0	300,000,000
Unamortized discount and deferred financing costs	(56,400,000)	(60,000,000)
Total convertible senior notes	$ 243,600,000	$ 240,000,000
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	$ 35,600,000
Debt instrument interest rate stated percentage	4.0625%