Fair Value Measurements (Details) (USD $)	9 Months Ended
	Sep. 30, 2014 Impaired_Asset_And_Liability	Sep. 30, 2013 Impaired_Asset_And_Liability	Dec. 31, 2013
Assets
Deferred compensation plan	$ 12,815,000		$ 12,507,000
Derivative contracts	19,445,000		13,792,000
Total assets	32,260,000		26,299,000
Liabilities
Deferred compensation plan	30,277,000		33,211,000
Derivative contracts	3,593,000		24,685,000
Total liabilities	33,870,000		57,896,000
Number of non-financial assets and liabilities impaired	0	0
Nonrecurring basis
Liabilities
Total liabilities	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Recurring basis
Assets
Deferred compensation plan	12,815,000		12,507,000
Derivative contracts	0		0
Total assets	12,815,000		12,507,000
Liabilities
Deferred compensation plan	30,277,000		33,211,000
Derivative contracts	0		0
Total liabilities	30,277,000		33,211,000
Significant Other Observable Inputs (Level 2) | Recurring basis
Assets
Deferred compensation plan	0		0
Derivative contracts	1,578,000		0
Total assets	1,578,000		0
Liabilities
Deferred compensation plan	0		0
Derivative contracts	1,216,000		6,983,000
Total liabilities	1,216,000		6,983,000
Significant Unobservable Inputs (Level 3) | Recurring basis
Assets
Deferred compensation plan	0		0
Derivative contracts	17,867,000		13,792,000
Total assets	17,867,000		13,792,000
Liabilities
Deferred compensation plan	0		0
Derivative contracts	2,377,000		17,702,000
Total liabilities	$ 2,377,000		$ 17,702,000