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Debt (Details) - USD ($)
1 Months Ended 3 Months Ended
Oct. 31, 2017
Sep. 30, 2017
Dec. 31, 2017
Sep. 30, 2017
Long Term Debt        
Write off of Deferred Debt Issuance Cost       $ 8,000,000
Subsequent Event [Member]        
Long Term Debt        
Write off of Deferred Debt Issuance Cost     $ 6,600,000  
4.125 Senior Notes Due 2025 [Member] | Senior Notes        
Long Term Debt        
Debt Instrument, Face Amount   $ 350,000,000   $ 350,000,000
Stated interest rate   4.125%   4.125%
6 3/8% Senior Notes, due 2022 | Senior Notes        
Long Term Debt        
Stated interest rate   6.375%   6.375%
6 3/8% Senior Notes, due 2022 | Senior Notes | Debt Instrument, Redemption, Period One [Member]        
Long Term Debt        
Redemption price of debt instrument (as a percent)   103.563%    
Debt Instrument, Repurchased Face Amount   $ 182,900,000   $ 182,900,000
6 3/8% Senior Notes, due 2022 | Senior Notes | Debt Instrument, Redemption, Period Two [Member]        
Long Term Debt        
Redemption price of debt instrument (as a percent) 103.188%      
Debt Instrument, Repurchased Face Amount $ 167,100,000