Significant Accounting Policies (Details Textuals) (USD $) Share data in Millions, unless otherwise specified	1 Months Ended	12 Months Ended
	Jan. 31, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Significant Accounting Policies [Line Items]
Reduction to CO2 properties				$ 26,100,000
Adjustment to accumulated depletion, depreciation and amortization				35,700,000
Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments		3,100,000
Net income attributable to noncontrolling interest		0	0	13,804,000
Cost basis of Vanguard investment				93,000,000
Interest and Other Income from Available-for-sale securities			7,200,000
Other than Temporary Impairment Loss on Investments			6,300,000
Proceeds from Sale of Available-for-sale Securities, Equity	83,500,000	83,545,000	0	0
Depletion, depreciation and amortization per BOE		18.69	16.42	15.82
Impairment of Goodwill		0	0	0
Non-vested restricted stock excluded from basic weighted average common shares		3.7	3.4	3.2
Post-tax [Member]
Significant Accounting Policies [Line Items]
Cumulative effect of change in accounting policy, before tax				6,000,000
Pre-tax [Member]
Significant Accounting Policies [Line Items]
Cumulative effect of change in accounting policy, before tax				$ 9,600,000
Encore Energy Partners LP ("ENP") [Member]
Significant Accounting Policies [Line Items]
Ownership Percentage In Subsidiaries				46.00%
Encore Energy Partners GP LLC ("GP LLC") [Member]
Significant Accounting Policies [Line Items]
Ownership Percentage In Subsidiaries				100.00%
Minimum [Member] | Co2 Property And Pipelines [Member]
Significant Accounting Policies [Line Items]
Estimated useful lives		15 years
Minimum [Member] | Vehicles and furniture and fixtures [Member]
Significant Accounting Policies [Line Items]
Estimated useful lives		5 years
Minimum [Member] | Computer equipment and software [Member]
Significant Accounting Policies [Line Items]
Estimated useful lives		3 years
Maximum [Member] | Co2 Property And Pipelines [Member]
Significant Accounting Policies [Line Items]
Estimated useful lives		50 years
Maximum [Member] | Vehicles and furniture and fixtures [Member]
Significant Accounting Policies [Line Items]
Estimated useful lives		10 years
Maximum [Member] | Computer equipment and software [Member]
Significant Accounting Policies [Line Items]
Estimated useful lives		5 years