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Debt - 2024 Notes (Details) - USD ($)
1 Months Ended 3 Months Ended 12 Months Ended
Mar. 28, 2015
Mar. 31, 2014
Sep. 30, 2017
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Nov. 30, 2014
Mar. 29, 2014
Debt Instrument [Line Items]                
Debt issuance costs       $ 11,900,000 $ 0 $ 0    
Loss on extinguishment of debt     $ (21,200,000) $ 21,200,000 $ 0 $ 14,300,000    
Senior notes | 2024 Notes                
Debt Instrument [Line Items]                
Proceeds from issuance of debt   $ 325,000,000            
Debt issuance costs   $ 3,900,000            
Senior notes | 2024 Notes | Prior to March 15, 2019                
Debt Instrument [Line Items]                
Percentage of debt redemption price       100.00%        
Senior notes | 2018 Notes                
Debt Instrument [Line Items]                
Aggregate principal amount of debt redeemed               $ 280,000,000
Senior notes | 2020 Notes                
Debt Instrument [Line Items]                
Aggregate principal amount of debt redeemed             $ 245,000,000  
Percentage of debt redemption 104.063% 10.00%            
Repayments of debt   $ 35,000,000