Earnings per Share - Dilutive and Antidilutive securities (Details) shares in Thousands, item in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) item shares	Dec. 31, 2015 shares	Dec. 31, 2014 shares
Antidilutive securities and effect of dilutive securities
Effect of dilutive securities - Convertible Notes (in shares) | shares	2,697	97	3,432
2017 Notes
Antidilutive securities and effect of dilutive securities
Amount by which if-converted value of the Notes are less than principal amount	$ 34.6
2018 Notes
Antidilutive securities and effect of dilutive securities
Amount by which if-converted value of the Notes exceed principal amount	22.7
2019 Notes
Antidilutive securities and effect of dilutive securities
Amount by which if-converted value of the Notes exceed principal amount	$ 33.1
Effect of dilutive securities - Convertible Notes (in shares) | shares	2,700
Convertible Senior Notes
Antidilutive securities and effect of dilutive securities
Potential shares of common stock contingently issuable upon conversion of the Convertible Notes | item	62.6
Shares excluded from diluted EPS calculations | shares	59,900
Convertible Senior Notes | 2017 Notes
Antidilutive securities and effect of dilutive securities
Amount by which if-converted value of the Notes are less than principal amount	$ 34.6
Effect of dilutive securities - Convertible Notes (in shares) | shares	0
Convertible Senior Notes | 2018 Notes
Antidilutive securities and effect of dilutive securities
Amount by which if-converted value of the Notes exceed principal amount	$ 22.7
Convertible Senior Notes | 2019 Notes
Antidilutive securities and effect of dilutive securities
Amount by which if-converted value of the Notes exceed principal amount	$ 33.1
Restricted stock
Antidilutive securities and effect of dilutive securities
Number of anti-dilutive common shares excluded from the calculation of diluted income per share | shares	600	1,500	2,000