Asset retirement obligations (“ARO”) (Tables)

9 Months Ended

Sep. 30, 2014

Asset Retirement Obligation Disclosure [Abstract]

Schedule of changes in asset retirement obligations

The reconciliation of the changes in the asset retirement obligations is presented below:

	Nine months ended September 30, 2014			Year ended December 31, 2013
Beginning balance, ARO liability	$	27,113		$	16,124
Additional ARO liability incurred	1,493			1,730
ARO liabilities settled	(3,547		)	(2,580		)
Accretion expense	1,114			1,733
Additional ARO liability from Sebree acquisition	—			10,106
Ending balance, ARO liability	$	26,173		$	27,113