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Summary of Significant Accounting Policies - Goodwill and Other Intangible Assets and Asset Retirement Obligations (Details)
 12 Months Ended
Dec. 31, 2015
Minimum [Member]  
Finite-Lived Intangible Assets [Line Items]  
Intangible assets, useful life 5 years
Useful life of asset retirement obligation 2 years
Maximum [Member]  
Finite-Lived Intangible Assets [Line Items]  
Intangible assets, useful life 20 years
Useful life of asset retirement obligation 25 years