Debt Textuals (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 Senior Notes 6 Point 30 Percentage Member	Dec. 31, 2011 $870 Credit Agreement	Dec. 31, 2011 $950 Credit Agreement	Dec. 31, 2011 Other Local Arrangements	Dec. 31, 2010 Tender Offer and Repayment of 4.85% Senior Notes	Dec. 31, 2009 Tender Offer and Repayment of 4.85% Senior Notes	Nov. 15, 2010 Tender Offer and Repayment of 4.85% Senior Notes
Debt Instrument
Senior Notes, Stated Interest Rate				6.30%						4.85%
Maturity Date				Jun. 25, 2015	Dec. 20, 2016		Jul. 01, 2012	Nov. 15, 2010
Minimum Prepayment Percent				10.00%
Percent of Price of Repayment				100.00%
Percent of Principal Balance Paid due to Change in Control of Company				100.00%
Consolidated Interest Coverage Ratio Covenant				3.5 to 1.0	3.5 to 1.0
Consolidated Leverage Ratio Covenant				3.5 to 1.0	3.25 to 1.0
Debt Instrument, Covenant Compliance				The Company was in compliance with these covenants at December 31, 2011.	the Company was in compliance as of December 31, 2011
Maximum Senior Note Issuance				$ 600,000,000
Debt issuance costs	3,144,000	0	670,000	700,000
Amortized Issuance Costs Period				six	2016
Credit Agreement Borrowing Capacity					870,000,000	950,000,000
$870 million Credit Agreement, Basis Spread on Variable Rate					1.05%
Gains (Losses) on Extinguishment of Debt						300,000
Interest Costs, Capitalized During Period					3,100,000
Line of Credit Facility, Remaining Borrowing Capacity					485,900,000
Other Local Arrangements	28,300,000	24,722,000					10,000,000
Debt, Weighted Average Interest Rate	4.00%	5.00%
Senior Notes, Face Amount				100,000,000						150,000,000
Tender Offer Expiration Date									May 12, 2009
Early Repayment of Senior Debt									75,000,000
Repayments of Senior Debt								$ 75,000,000