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Debt - Schedule of Components of Long-term Debt (Details) - USD ($)
Mar. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Debt Instrument [Line Items]      
Other debt $ 20,700,000 $ 21,300,000  
Total 646,800,000 644,700,000  
Less – current maturities 10,600,000 10,800,000  
Total long-term debt 636,200,000 633,900,000  
5.50% convertible senior notes due March 1, 2021      
Debt Instrument [Line Items]      
Face value     $ 1,000
Senior Notes | 10.75% senior notes due April 15, 2022      
Debt Instrument [Line Items]      
Face value 440,000,000 440,000,000  
Unamortized discount and fees 9,800,000 10,400,000  
Senior notes 430,200,000 429,600,000  
Senior Notes | 5.50% convertible senior notes due March 1, 2021      
Debt Instrument [Line Items]      
Face value 213,500,000 213,500,000 $ 213,500,000.0
Unamortized discount and fees 25,300,000 27,200,000  
Senior notes 188,200,000 186,300,000  
Capital Lease Obligations      
Debt Instrument [Line Items]      
Capital leases $ 7,700,000 $ 7,500,000