Business Combination Business Combination (Details) shares in Millions	3 Months Ended	9 Months Ended
	Dec. 31, 2016 USD ($) a Wells shares	Sep. 30, 2017 USD ($)
Business Acquisition [Line Items]
Oil and gas producing wells, gross		2,900
Goodwill	$ 62,041,000	$ 0
Delaware Basin Acquisition [Member]
Business Acquisition [Line Items]
Stock Issued During Period, Shares, Acquisitions | shares	9.4
Gas and Oil Area, Developed, Gross | a	57,900
Oil and gas producing wells, gross | Wells	30
Payments to Acquire Business Two, Net of Cash Acquired		905,962,000
Payments for Deposits Applied to Debt Retirements		40,000,000
Payments to Acquire Businesses, Gross	$ 945,962,000	945,962,000
Business Combination, Consideration Transferred, Equity Interests Issued and Issuable		690,702,000
Goodwill, Purchase Accounting Adjustments		426,000
Business Combination, Consideration Transferred		1,637,090,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Prepaid Expense and Other Assets		6,401,000
Business Acquisitions Purchase Price Allocation Proved Natural Gas Properties		216,000,000
business acquisition purchase price allocation unproved properties		1,697,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Equipment		33,153,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment		12,323,000
Goodwill	$ 62,041,000	75,121,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets		2,039,998,000
Business Combination, Contingent Consideration, Liability, Current		(24,496,000)
Business Acquisition Purchase Price Allocation Asset Retirement Obligation		(3,705,000)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities		(374,707,000)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities		(402,908,000)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net		$ 1,637,090,000