Fair Value of Financial Instruments - Notes Payable (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016	Sep. 23, 2016	Jun. 30, 2015	Jan. 31, 2013
Notes Payable | 11% PhaRMA Notes
Fair value disclosures
Aggregate principal amount of notes issued in private placement					$ 175.0
Notes Payable | 11% PhaRMA Notes | Significant Unobservable Inputs (Level 3)
Fair value disclosures
Estimated fair value	$ 134.9
Notes Payable | 8.375% Notes due 2026
Fair value disclosures
Aggregate principal amount of notes issued in private placement			$ 150.0
Notes Payable | 8.375% Notes due 2026 | Significant Unobservable Inputs (Level 3)
Fair value disclosures
Aggregate principal amount of notes issued in private placement			$ 150.0
Estimated fair value	155.8
Convertible Senior Notes | 2.25% Convertible Senior Notes due in 2022
Fair value disclosures
Aggregate principal amount of notes issued in private placement				$ 335.7
Convertible Senior Notes | 2.25% Convertible Senior Notes due in 2022 | Significant Other Observable Inputs (Level 2)
Fair value disclosures
Estimated fair value	$ 450.5	$ 384.2