Properties, Plant and Equipment - Oil and Gas Properties - Tabular Information (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016
Mineral interests in properties
Unproved	$ 190,722		$ 213,153
Proved	882,386		1,054,683
Wells and equipment and related facilities	1,375,932		1,395,291
Gross oil and gas properties	2,449,040		2,663,127
Less: Accumulated depletion and impairment	(870,301)		(919,539)
Net oil and gas properties	$ 1,578,739	$ 1,559,861	$ 1,743,588

Capitalized costs which include those incurred to (1) to drill and equip those exploratory wells and exploratory-type stratigraphic test wells that have found proved reserves and (2) obtain access to proved reserves and provide facilities for extracting, treating, gathering, storing the oil and gas, including the drilling and equipping of development wells and development-type stratigraphic wells and service wells.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Amount of accumulated depreciation, depletion, amortization and impairment of oil and gas property carried under the successful effort method.

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Oil and Gas properties, gross, carried under the successful effort method.

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Oil and gas properties net of accumulated depreciation, depletion, amortization, impairment, and abandonment, carried under the successful effort method.

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Oil and Gas properties with proved reserves under the successful effort method.

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Oil and Gas properties with unproved reserves under the successful effort method.

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