Summary of Significant Accounting Policies (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Summary of Significant Accounting Policies [Line Items]
Net Cash Used in Investing Activities	$ 229,015,000	$ (7,765,000)	$ (234,736,000)
Net Cash Provided by Operating Activities	372,370,000	310,228,000	483,907,000
Maximum amount of time between receipt and application of Federal aid funds	3 days
Revision Adjustment [Member]
Summary of Significant Accounting Policies [Line Items]
Net Cash Used in Investing Activities		17,636,000	(6,693,000)
Net Cash Provided by Operating Activities		(17,636,000)	6,693,000
Impact on previously reported cash and cash equivalents, Consolidated Balance Sheets or Consolidated Statement of Operations	0
Previously Reported [Member]
Summary of Significant Accounting Policies [Line Items]
Net Cash Used in Investing Activities		(25,401,000)	(228,043,000)
Net Cash Provided by Operating Activities		$ 327,864,000	$ 477,214,000
Minimum [Member] | Machinery and Equipment [Member]
Summary of Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life (in years)	3 years
Minimum [Member] | Building [Member]
Summary of Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life (in years)	20 years
Maximum [Member]
Summary of Significant Accounting Policies [Line Items]
Amortized Intangible Assets, Useful Life (in years)	10 years
Investment maturity length	3 months
Maximum [Member] | Machinery and Equipment [Member]
Summary of Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life (in years)	20 years
Maximum [Member] | Building [Member]
Summary of Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life (in years)	50 years