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Debt - 2023 Senior Notes (Details) - 2023 Senior Notes - USD ($)
Aug. 17, 2015
Oct. 31, 2017
Sep. 30, 2017
Debt Instrument [Line Items]      
Interest rate 7.875%    
Percent of principal amount of debt that may be redeemed (up to) 35.00%    
Redemption price 107.875%    
Percent of original principal amount of debt outstanding (at least) 65.00%    
Repurchase price of principal amount of notes plus accrued and unpaid interest 100.00%    
Aggregate principal that must be held to accelerate amounts due (not less than) 25.00%    
Carrying value, net     $ 490,500,000
Change Of Control      
Debt Instrument [Line Items]      
Repurchase price of principal amount of notes plus accrued and unpaid interest 101.00%    
CBR      
Debt Instrument [Line Items]      
Aggregate principal amount of debt issued $ 500,000,000   $ 500,000,000
Subsequent Event      
Debt Instrument [Line Items]      
Repurchased amount   $ 25,000,000