Capital expenditures related to oil and natural gas producing activities (Details 2) $ in Thousands	12 Months Ended
	Dec. 31, 2014 USD ($)
Acquisitions:
Proved properties	$ 87,919	[1]
Unproved properties	138,683	[1]
Exploration	16,879	[1]
Development	331,400	[1]
Total capital expenditures	574,881	[1]
Net change in property, plant and equipment related to future liabilities for asset retirement obligations that are excluded	$ (9,000)

[1] Excludes net reductions to property, plant and equipment related to the recognition of future liabilities for asset retirement obligations associated with the plugging and abandonment of oil and natural gas wells of $9.0 million for the year ended December 31, 2014.