Debt Level 4 (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Debt Instrument [Line Items]
Bank credit facility due March 2016	$ 77,000	$ 65,000
Total debt	1,914,123	1,884,670
Less current maturities	(31,289)	(23,554)
Total long-term debt	1,882,834	1,861,116
Unsecured Debt [Member]
Debt Instrument [Line Items]
Unamortized pricing discounts and other	(4,445)	(4,888)
Unsecured Debt [Member] | February 2013 [Member]
Debt Instrument [Line Items]
Senior Notes	4,757	4,757
Unsecured Debt [Member] | October 2014 [Member]
Debt Instrument [Line Items]
Senior Notes	180,692	180,692
Unsecured Debt [Member] | April 2015 [Member]
Debt Instrument [Line Items]
Senior Notes	136,465	136,465
Unsecured Debt [Member] | April 2016 [Member]
Debt Instrument [Line Items]
Senior Notes	197,377	197,377
Unsecured Debt [Member] | June 2017 [Member]
Debt Instrument [Line Items]
Senior Notes	295,000	295,000
Unsecured Debt [Member] | October 2018 [Member]
Debt Instrument [Line Items]
Senior Notes	250,000	250,000
Unsecured Debt [Member] | May 2019 [Member]
Debt Instrument [Line Items]
Senior Notes	250,000	250,000
Unsecured Debt [Member] | November 2021 [Member]
Debt Instrument [Line Items]
Senior Notes	150,000	150,000
Unsecured Debt [Member] | April 2027 [Member]
Debt Instrument [Line Items]
Senior Notes	200,000	200,000
Capital Lease Obligations [Member]
Debt Instrument [Line Items]
Obligations under capital leases	171,427	124,330
Mortgages [Member]
Debt Instrument [Line Items]
Mortgage notes and other debt, maturities through 2047	$ 5,850	$ 35,937