Debt Schedule Of Components Of Debt (Details) (USD $)														6 Months Ended	12 Months Ended
	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2014 Senior Notes [Member] $400 Million Senior Notes [Member]	Dec. 31, 2013 Senior Notes [Member] $400 Million Senior Notes [Member]	Jun. 27, 2012 Senior Notes [Member] $400 Million Senior Notes [Member]	Jun. 30, 2014 Senior Notes [Member] $250 Million Senior Notes [Member]	Dec. 31, 2013 Senior Notes [Member] $250 Million Senior Notes [Member]	Aug. 25, 2010 Senior Notes [Member] $250 Million Senior Notes [Member]	Jun. 30, 2014 Senior Secured Credit Facility [Member] $350 Million Senior Secured Credit Facility [Member]	Dec. 31, 2013 Senior Secured Credit Facility [Member] $350 Million Senior Secured Credit Facility [Member]	Jul. 25, 2012 Senior Secured Credit Facility [Member] $350 Million Senior Secured Credit Facility [Member]	Jun. 30, 2014 Economic Development Loans [Member]	Dec. 31, 2013 Economic Development Loans [Member]	Jun. 30, 2014 Capital Lease Obligations [Member]	Dec. 31, 2013 Capital Lease Obligations [Member]	Jun. 30, 2014 Other Notes Payable [Member]	Dec. 31, 2013 Other Notes Payable [Member]
Debt [Line Items]
Total debt	$ 789,506,000	$ 793,559,000	$ 400,000,000	$ 400,000,000		$ 249,604,000	$ 249,572,000		$ 135,000,000	$ 138,750,000		$ 3,360,000	$ 3,360,000	$ 1,499,000	$ 1,848,000	$ 43,000	$ 29,000
Less current portion	11,970,000	10,088,000
Total long-term debt	777,536,000	783,471,000
Debt instrument face amount					400,000,000			250,000,000			350,000,000
Debt instrument effective interest rate (percentage)			5.94%	5.94%	5.94%	6.19%	6.19%	6.19%	2.15%	2.17%		3.00%	3.00%	3.18%	3.18%
Senior notes, discount						$ 400,000	$ 400,000	$ 600,000
Capital lease maturity year														2016	2016