Debt Schedule Of Components Of Debt (Details) (USD $)	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 Senior Notes [Member] 400 Million Senior Notes [Member]	Dec. 31, 2012 Senior Notes [Member] 400 Million Senior Notes [Member]	Jun. 27, 2012 Senior Notes [Member] 400 Million Senior Notes [Member]	Mar. 31, 2013 Senior Notes [Member] 250 Million Senior Notes [Member]	Dec. 31, 2012 Senior Notes [Member] 250 Million Senior Notes [Member]	Aug. 25, 2010 Senior Notes [Member] 250 Million Senior Notes [Member]	Mar. 31, 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]	Mar. 31, 2013 Capital Lease Obligations [Member]	Dec. 31, 2012 Capital Lease Obligations [Member]	Mar. 31, 2013 Other Notes Payable [Member]	Dec. 31, 2012 Other Notes Payable [Member]
Total debt	$ 871,315,000	$ 855,345,000	$ 400,000,000	$ 400,000,000		$ 249,524,000	$ 249,508,000		$ 219,375,000	$ 203,250,000		$ 2,352,000	$ 2,519,000	$ 64,000	$ 68,000
Less current portion	(8,201,000)	(8,195,000)
Total long-term debt	863,114,000	847,150,000
Debt instrument face amount					400,000,000			250,000,000			350,000,000
Debt instruments effective interest rate			5.94%	5.94%	5.94%	6.19%	6.19%	6.19%	2.59%	2.66%		3.18%	3.18%
Senior notes, discount						$ 500,000	$ 500,000	$ 600,000
Capital Lease Maturity Year												2016	2016