Significant Accounting Policies (Property Plant and Equipment & Intangible Assets) (Details)	12 Months Ended
	Dec. 31, 2016
Building and building improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment useful life	40 years
Building and building improvements | NACoal
Property, Plant and Equipment [Line Items]
Property, plant and equipment useful life	30 years
Machinery and equipment | Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment useful life	3 years
Machinery and equipment | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment useful life	15 years