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 |