Quarterly report pursuant to Section 13 or 15(d)

Long-term Debt - Summary of Components of Convertible Notes (Details)

v3.8.0.1
Long-term Debt - Summary of Components of Convertible Notes (Details) - Convertible Senior Notes [Member] - 4.125% Convertible Senior Notes Due September 1, 2022 [Member] - USD ($)
Mar. 31, 2018
Dec. 31, 2017
Debt Instrument [Line Items]    
Principal $ 150,000,000 $ 150,000,000
Accrued interest 1,000,000 3,000,000
Unamortized financing costs (5,000,000) (5,000,000)
Carrying value of convertible notes $ 146,000,000 $ 148,000,000