Commitments and Contingencies (Details) (USD $)	12 Months Ended												12 Months Ended	1 Months Ended	12 Months Ended			3 Months Ended
	Dec. 31, 2011 Rigs	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2006 Airplane	Dec. 31, 2011 Vehicles	Dec. 31, 2011 Corporate and Field Offices	Dec. 31, 2011 Drilling rig commitments		Dec. 31, 2011 Other commitments		Dec. 31, 2011 Firm natural gas transportation contracts		Dec. 31, 2011 Uinta	Jul. 31, 2009 East Texas	Dec. 31, 2011 East Texas	Dec. 31, 2010 East Texas	Dec. 31, 2009 East Texas	Dec. 31, 2011 Questar Contracts Contingent on Chipeta Plant Expansion
Operating leases
Operating lease (in years)				10 years	3 years	5 years
Rent expense related to lease commitments	$ 2,600,000	$ 2,600,000	$ 2,600,000
Number of drilling rigs committed	4
Operating Leases, Future Minimum Payments Due
Operating Leases, Future Minimum Payments Due	11,800,000
Operating Leases, Future Minimum Payments Due, Current	2,800,000
Operating Leases, Future Minimum Payments, Due in Two Years	2,800,000
Operating Leases, Future Minimum Payments, Due in Three Years	2,600,000
Operating Leases, Future Minimum Payments, Due in Four Years	2,200,000
Operating Leases, Future Minimum Payments, Due in Five Years	1,400,000
Operating Leases, Future Minimum Payments, Due after Fifth Year	0
Unrecorded Unconditional Purchase Obligation Payment Schedule
Unrecorded Unconditional Purchase Obligation							7,000,000	[1]	31,300,000		263,500,000	[2]
Unrecorded Unconditional Purchase Obligation Due within One Year							7,000,000	[1]	14,200,000	[3]	29,700,000	[2]
Unrecorded Unconditional Purchase Obligation Due in Second Year							0	[1]	11,400,000	[3]	30,200,000	[2]
Unrecorded Unconditional Purchase Obligation Due in Third Year							0	[1]	1,800,000	[3]	32,700,000	[2]
Unrecorded Unconditional Purchase Obligation Due in Fourth Year							0	[1]	1,900,000	[3]	32,600,000	[2]
Unrecorded Unconditional Purchase Obligation Due in Fifth Year							0	[1]	2,000,000	[3]	32,500,000	[2]
Unrecorded Unconditional Purchase Obligation Due after Fifth Year							0	[1]	0	[3]	105,800,000	[2]
Recorded Unconditional Purchase Obligation and Operating Leases, Future Minimum Payments Due
Unrecorded Unconditional Purchase Obligation and Operating Leases, Future Minimum Payments Due	313,600,000
Unrecorded Unconditional Purchase Obligation Due and Operating Leases, Future Minimum Payments Due, Current	53,700,000
Unrecorded Unconditional Purchase Obligation Due and Operating Leases, Future Minimum Payments Due with Second Year	44,400,000
Unrecorded Unconditional Purchase Obligation Due and Operating Leases, Future Minimum Payments Due with Third Year	37,100,000
Unrecorded Unconditional Purchase Obligation Due and Operating Leases, Future Minimum Payments Due with Fourth Year	36,700,000
Unrecorded Unconditional Purchase Obligation Due and Operating Leases, Future Minimum Payments Due within Fifth Year	35,900,000
Unrecorded Unconditional Purchase Obligation Due and Operating Leases, Future Minimum Payments Due after Fifth Year	105,800,000
Proposed transportation of gas under transportation service agreements with Questar Pipeline Company (in years)																		8 years
Volume for proposed transportation of gas under transportation service agreements with Questar Pipeline Company (in MMBtu/D)																		6,200
Uinta Crude Oil Sales Contract
Sales contract, minimum purchase of light crude oil (in Bbl/D)													5,000
Gross oil production average (in Bbl/D)													3,390
E. Texas Gathering System
Proceeds from gas gathering system, financing obligation														18,400,000
Net book value of property														16,700,000
Gas gathering system, costs incurred	$ 13,038,000	$ 19,896,000	$ 21,231,000												$ 5,300,000	$ 6,700,000	$ 2,000,000

[1] Excludes obligations related to rigs drilling on a well-by-well basis that can be released after drilling the current well without penalty.

[2] Includes a transportation agreement with Questar Pipeline Company for an average of 6,200 MMBtu/D of firm transportation over a period of eight years, based on the expectation that the expansion of the Chipeta Processing LLC natural gas plant expansion will be completed and transportation under this contract will begin July 1, 2012.

[3] Includes primarily obligations related to natural gas purchases, cogeneration facility management services and equipment rentals.