Debt (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Long term debt
Long-term Debt, Total	$ 350,695	$ 326,609
Less current maturities	21,199	5,885
Long-term Debt, Noncurrent	329,496	320,724
Parent Company [Member]
Long term debt
Long-term Debt, Total	300,320	300,939
Parent Company [Member] | 8% unsecured notes due December 2019 [Member]
Long term debt
Long-term Debt, Total	173,578	173,578
Parent Company [Member] | 7.625% unsecured notes due March 2027 [Member]
Long term debt
Long-term Debt, Total	116,880	116,880
Parent Company [Member] | Capitalized leases and other [Member]
Long term debt
Long-term Debt, Total	9,862	10,481
Subsidiaries [Member]
Long term debt
Long-term Debt, Total	50,375	25,670
Subsidiaries [Member] | 5.13% unsecured notes due in 2011 [Member]
Long term debt
Long-term Debt, Total	0	5,285
Subsidiaries [Member] | 5.795% to 6.3175% unsecured notes due in 2012 [Member]
Long term debt
Long-term Debt, Total	20,599	20,385
Subsidiaries [Member] | 6.10% to 6.65% unsecured notes due in 2014 [Member]
Long term debt
Long-term Debt, Total	26,528	0
Subsidiaries [Member] | 2.25% unsecured notes due in 2016 [Member]
Long term debt
Long-term Debt, Total	$ 3,248	$ 0