Fair Value Measurements (Details) (USD $) In Thousands	Sep. 30, 2011
Fair Value Hierarchy Table for Assets and Liabilities Measured at Fair Value
Derivative assets liabilities at fair value net	$ 183,600
Fair Value, Measurements, Recurring [Member]
Fair Value Hierarchy Table for Assets and Liabilities Measured at Fair Value
Trading securities held in our deferred compensation plans	49,199
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets [Member]
Fair Value Hierarchy Table for Assets and Liabilities Measured at Fair Value
Trading securities held in our deferred compensation plans	49,199
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets [Member] | Call Option [Member]
Fair Value Hierarchy Table for Assets and Liabilities Measured at Fair Value
Derivative assets liabilities at fair value net	0
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets [Member] | Collars [Member]
Fair Value Hierarchy Table for Assets and Liabilities Measured at Fair Value
Derivative assets liabilities at fair value net	0
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets [Member] | Swap [Member]
Fair Value Hierarchy Table for Assets and Liabilities Measured at Fair Value
Derivative assets liabilities at fair value net	0
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs [Member]
Fair Value Hierarchy Table for Assets and Liabilities Measured at Fair Value
Trading securities held in our deferred compensation plans	0
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs [Member] | Call Option [Member]
Fair Value Hierarchy Table for Assets and Liabilities Measured at Fair Value
Derivative assets liabilities at fair value net	(20,737)
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs [Member] | Collars [Member]
Fair Value Hierarchy Table for Assets and Liabilities Measured at Fair Value
Derivative assets liabilities at fair value net	148,161
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs [Member] | Swap [Member]
Fair Value Hierarchy Table for Assets and Liabilities Measured at Fair Value
Derivative assets liabilities at fair value net	56,185
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs [Member]
Fair Value Hierarchy Table for Assets and Liabilities Measured at Fair Value
Trading securities held in our deferred compensation plans	0
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs [Member] | Call Option [Member]
Fair Value Hierarchy Table for Assets and Liabilities Measured at Fair Value
Derivative assets liabilities at fair value net	0
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs [Member] | Collars [Member]
Fair Value Hierarchy Table for Assets and Liabilities Measured at Fair Value
Derivative assets liabilities at fair value net	0
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs [Member] | Swap [Member]
Fair Value Hierarchy Table for Assets and Liabilities Measured at Fair Value
Derivative assets liabilities at fair value net	0
Fair Value, Measurements, Recurring [Member] | Call Option [Member]
Fair Value Hierarchy Table for Assets and Liabilities Measured at Fair Value
Derivative assets liabilities at fair value net	(20,737)
Fair Value, Measurements, Recurring [Member] | Collars [Member]
Fair Value Hierarchy Table for Assets and Liabilities Measured at Fair Value
Derivative assets liabilities at fair value net	148,161
Fair Value, Measurements, Recurring [Member] | Swap [Member]
Fair Value Hierarchy Table for Assets and Liabilities Measured at Fair Value
Derivative assets liabilities at fair value net	$ 56,185