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Other Long-term Liabilities, Mandatorily Redeemable Preferred Interests (Details)
$ in Millions
3 Months Ended
Mar. 31, 2017
USD ($)
JointVenture
Mar. 31, 2016
USD ($)
Changes in long-term liabilities attributable to mandatorily redeemable preferred interests [Abstract]    
Balance at December 31, 2016 $ 68.5  
Change in estimated redemption value included in interest expense 2.5 $ (18.5)
Balance at March 31, 2017 71.9  
Mandatorily Redeemable Noncontrolling Interests [Member]    
Changes in long-term liabilities attributable to mandatorily redeemable preferred interests [Abstract]    
Balance at December 31, 2016 68.5  
Income attributable to mandatorily redeemable preferred interests 0.9  
Change in estimated redemption value included in interest expense 2.5  
Balance at March 31, 2017 $ 71.9  
Mandatorily Redeemable Noncontrolling Interests [Member] | West OK [Member]    
Changes in long-term liabilities attributable to mandatorily redeemable preferred interests [Abstract]    
Ownership interest 100.00%  
Mandatorily Redeemable Noncontrolling Interests [Member] | West TX [Member]    
Changes in long-term liabilities attributable to mandatorily redeemable preferred interests [Abstract]    
Ownership interest 72.80%  
Mandatorily Redeemable Noncontrolling Interests [Member] | Joint Ventures [Member]    
Changes in long-term liabilities attributable to mandatorily redeemable preferred interests [Abstract]    
Number of joint ventures | JointVenture 2