Accumulated Other Comprehensive Income (Loss) (Details) (USD $)	Sep. 30, 2011	Dec. 31, 2010
Accumulated other comprehensive loss, net of tax	$ (35,500,000)	$ (60,200,000)
Noncontrolling Interest
Accumulated other comprehensive loss, net of tax	(3,700,000)	(5,800,000)
Atoka Noncontrolling Interest [Member]
Accumulated other comprehensive loss, net of tax	0	0
Parent [Member]
Accumulated other comprehensive loss, net of tax	(39,200,000)	(66,000,000)
Pension Plans, Defined Benefit [Member] | Defined Benefit Plans Income Loss [Member]
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax	(29,400,000)	(31,100,000)
Pension Plans, Defined Benefit [Member] | Defined Benefit Plan Prior Service Cost [Member]
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax	(200,000)	(500,000)
Other Postretirement Benefit Plans, Defined Benefit [Member] | Defined Benefit Plans Income Loss [Member]
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax	(12,300,000)	(13,600,000)
Other Postretirement Benefit Plans, Defined Benefit [Member] | Defined Benefit Plan Prior Service Cost [Member]
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax	9,300,000	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Defined Benefit Plan Net Transition Obligation [Member]
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax	(200,000)	(300,000)
Commodity Contract [Member]
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax	(5,600,000)	(19,500,000)
Interest Rate Swap [Member]
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax	$ (800,000)	$ (1,000,000)