Supplementary information (Tables)

6 Months Ended

Jun. 30, 2014

Oil and Gas Exploration and Production Industries Disclosures [Abstract]

Schedule of costs incurred in the development of oil and natural gas properties

Costs incurred in the acquisition, exploration and development of oil and natural gas assets are presented below for the periods presented:

	Three months ended June 30,				Six months ended June 30,
(in thousands)	2014		2013		2014		2013
Property acquisition costs:							—
Proved	$	3,848	$	—	$	3,873	$	—
Unproved	2,645		—		9,925		—
Exploration	8,143		12,167		16,642		20,928
Development costs(1)	220,240		165,416		408,553		322,732
Total costs incurred	$	234,876	$	177,583	$	438,993	$	343,660

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(1) The costs incurred for oil and natural gas development activities include $0.9 million and $0.7 million in asset retirement obligations for the three months ended June 30, 2014 and 2013, respectively, and $1.5 million and $1.3 million for the six months ended June 30, 2014 and 2013, respectively.