Annual report pursuant to Section 13 and 15(d)

Financing Arrangements - Liability Components of Financing Arrangements (Details)

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Financing Arrangements - Liability Components of Financing Arrangements (Details) - USD ($)
$ in Thousands
Dec. 31, 2017
Dec. 31, 2016
2019 Convertible Senior Notes    
Total current portion of notes payable $ 224,529 $ 212,910
2019 Convertible Senior Notes    
2019 Convertible Senior Notes    
Principal amount outstanding 245,000 245,000
Unamortized discount $ (20,471) $ (32,090)