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Other Long-term Liabilities, Mandatorily Redeemable Preferred Interests (Details) - Mandatorily Redeemable Noncontrolling Interests [Member]
Jun. 30, 2018
JointVenture
West OK [Member]  
Changes in long-term liabilities attributable to mandatorily redeemable preferred interests [Abstract]  
Ownership interest 100.00%
West TX [Member]  
Changes in long-term liabilities attributable to mandatorily redeemable preferred interests [Abstract]  
Ownership interest 72.80%
Joint Ventures [Member]  
Changes in long-term liabilities attributable to mandatorily redeemable preferred interests [Abstract]  
Number of joint ventures 2