Accounting Policies (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014
Statutory Accounting Practices
Mineral rights	$ 2,400,000	$ 4,700,000
Future lease bonus payments	94,600
Deferred finance costs, net	112,918	89,100
Deferred finance costs, current	$ 65,600	$ 25,500
Exploration and Production Equipment [Member] \| Minimum [Member]
Statutory Accounting Practices
Estimated useful life	5 years
Exploration and Production Equipment [Member] \| Maximum [Member]
Statutory Accounting Practices
Estimated useful life	32 years
Building and Building Improvements [Member] \| Minimum [Member]
Statutory Accounting Practices
Estimated useful life	10 years
Building and Building Improvements [Member] \| Maximum [Member]
Statutory Accounting Practices
Estimated useful life	30 years
Mining Properties and Mineral Rights [Member] \| Minimum [Member]
Statutory Accounting Practices
Term of contract	10 years
Mining Properties and Mineral Rights [Member] \| Maximum [Member]
Statutory Accounting Practices
Term of contract	50 years
Capital Addition Purchase Commitments [Member]
Statutory Accounting Practices
Future lease bonus payments	$ 60,000

Net amount of current deferred finance costs capitalized at the end of the reporting period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.8)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28555-108399

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 8
-Article 5

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28555-108399

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 3: http://www.xbrl.org/2003/role/presentationRef
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Carrying amount at the balance sheet date of mineral rights, or rights to extract a mineral from the earth or to receive payment in the form of a royalty for the extraction of minerals, net of amortization.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=6919630

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Amount of the fixed and determinable portion of the unrecorded unconditional purchase obligation maturing in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 440
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-Section 50
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