Asset Retirement Obligations (Details) - USD ($)		12 Months Ended
		Dec. 31, 2017		Dec. 31, 2016
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning asset retirement obligations		$ 123,307,000	[1],[2]	$ 140,874,000
Liabilities incurred	[3]	7,588,000		21,293,000
Liabilities settled	[4]	(30,432,000)		(57,100,000)
Accretion expense		5,988,000		7,795,000
Revision to estimated cash flows		8,019,000		10,445,000
Ending asset retirement obligations	[1],[2]	114,470,000		123,307,000
Asset retirement obligations associated with oil and gas properties held for sale		11,369,000		26,241,000
Current asset retirement obligation liability		$ 75,000		$ 932,000

[1] Balances as of December 31, 2017, and 2016, included $11.4 million and $26.2 million, respectively, of asset retirement obligations associated with oil and gas properties held for sale.

[2] Balances as of December 31, 2017, and 2016, included $75,000 and $932,000, respectively, related to the Company’s current asset retirement obligation liability, which is recorded in accounts payable and accrued expenses on the accompanying balance sheets.

[3] Reflects liabilities incurred through drilling activities and acquisitions of drilled wells.

[4] Reflects liabilities settled through plugging and abandonment activities and divestitures of properties.