Income Taxes (Details Textuals) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Statement Income Taxes Details [Abstract]
Excess Tax Benefit from Share-based Compensation, Financing Activities	$ 6,212,000	$ 17,522,000	$ 14,213,000
Withholding Tax On Share Repurchase Transactions	0	0	0
Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate	35.00%
U.S. federal alternative minimum tax credits	11,600,000
Foreign tax credit carryforward	1,700,000
Canadian Operating Loss Carryforward	2,700,000
Deferred tax asset or liability unrealized gains and losses on derivative instruments	82,700,000	46,200,000
Unutilized Capital Loss Carryforwards	$ 5,400,000