Debt Schedule Of Components Of Debt (Details) (USD $)														9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 Senior Unsecured Notes [Member] $400 Million Senior Notes [Member]	Dec. 31, 2012 Senior Unsecured Notes [Member] $400 Million Senior Notes [Member]	Jun. 27, 2012 Senior Unsecured Notes [Member] $400 Million Senior Notes [Member]	Sep. 30, 2013 Senior Unsecured Notes [Member] $250 Million Senior Notes [Member]	Dec. 31, 2012 Senior Unsecured Notes [Member] $250 Million Senior Notes [Member]	Aug. 25, 2010 Senior Unsecured Notes [Member] $250 Million Senior Notes [Member]	Sep. 30, 2013 Senior Secured Credit Facility [Member] $350 Million Senior Secured Credit Facility [Member]	Dec. 31, 2012 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]	Sep. 30, 2013 Economic Development Loans	Dec. 31, 2012 Economic Development Loans	Sep. 30, 2013 Capital Lease Obligations [Member]	Dec. 31, 2012 Capital Lease Obligations [Member]	Sep. 30, 2013 Other Notes Payable [Member]	Dec. 31, 2012 Other Notes Payable [Member]
Total debt	$ 825,089,000	$ 855,345,000	$ 400,000,000	$ 400,000,000		$ 249,556,000	$ 249,508,000		$ 170,125,000	$ 203,250,000		$ 3,360,000		$ 2,017,000	$ 2,519,000	$ 31,000	$ 68,000
Less current portion	9,132,000	8,195,000
Total long-term debt	815,957,000	847,150,000
Debt instrument face amount					400,000,000			250,000,000			350,000,000
Debt instrument effective interest rate			5.94%	5.94%	5.94%	6.19%	6.19%	6.19%	2.52%	2.66%		3.00%		3.18%	3.18%
Senior notes, discount						$ 400,000	$ 500,000	$ 600,000
Capital Lease Maturity Year														2016	2016