Business Combination Business Combination (Details) a in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) a Wells
Business Acquisition [Line Items]
Escrow Deposit Disbursements Related to Property Acquisition	$ 21,000
Business Acquisition Purchase Price Allocation Asset Retirement Obligation	$ (4,687)
Oil and gas producing wells, gross	3,000
Bayswater Acquisition [Member]
Business Acquisition [Line Items]
Payments to Acquire Business Two, Net of Cash Acquired	$ 171,091
Payments to Acquire Businesses, Gross	192,091
Purchase Accounting Adjustments	9,734
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Prepaid Expense and Other Assets	517
Business Acquisitions Purchase Price Allocation Proved Natural Gas Properties	208,279
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment	2,796
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	211,592
Business Combination, Contingent Consideration, Liability, Current	(5,080)
Business Acquisition Purchase Price Allocation Asset Retirement Obligation	(4,687)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities	(9,767)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net	$ 201,825
Acquired Acreage | a	7,400
Oil and gas drilling locations, gross | Wells	220
Productive Oil Wells, Number of Wells, Net | Wells	24