Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2011

Commitments and Contingencies Disclosure [Abstract]

Schedule of future minimum rental payments for operating leases

(in millions)	Total		2012		2013		2014		2015		2016		Thereafter
Operating leases(1)	$	11.8	$	2.8	$	2.8	$	2.6	$	2.2	$	1.4	$	—
Drilling rig commitments(2)	7.0		7.0		—		—		—		—		—
Other commitments(3)	31.3		14.2		11.4		1.8		1.9		2.0		—
Firm natural gas transportation contracts(4)	263.5		29.7		30.2		32.7		32.6		32.5		105.8
Total	$	313.6	$	53.7	$	44.4	$	37.1	$	36.7	$	35.9	$	105.8

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(1) Includes operating leases related to office facilities, vehicles and aircraft.

(2) Excludes obligations related to rigs drilling on a well-by-well basis that can be released after drilling the current well without penalty.

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

(4) 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.