Income Taxes (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Effective tax rate of provision for income taxes	40.90%	38.50%	39.30%
Net current deferred income tax liability	$ 24,353,000	$ 106,123,000
Income taxes paid	18,787,000	818,000	4,198,000
Operating Loss Carryforwards	411,994,000	217,276,000
Alternative minimum tax credit carryforward	76,864,000	89,016,000
Statutory depletion carryforward	12,900,000
Windfalls Included In Net Operating Loss Carryforwards But Not Reflected In Deferred Tax Assets	131,300,000
Deferred Tax Assets, Valuation Allowance	2,900,000
Net long-term deferred tax liabilities	1,526,700,000	1,045,500,000
Federal [Member]
Income taxes paid	15,500,000
Operating Loss Carryforwards	1,174,700,000
State [Member]
Income taxes paid	3,300,000	800,000
Operating Loss Carryforwards	878,000,000
Minimum [Member]
Net operating loss carryforwards expiration date	Dec. 31, 2028
Maximum [Member]
Net operating loss carryforwards expiration date	Dec. 31, 2032
Exploration Program in Canada [Member]
Net operating loss carryforward	$ 22,300,000
Exploration Program in Canada [Member] | Minimum [Member]
Net operating loss carryforwards expiration date	Jan. 01, 2030
Exploration Program in Canada [Member] | Maximum [Member]
Net operating loss carryforwards expiration date	Dec. 31, 2033