Asset Retirement Obligation (Tables)

3 Months Ended

Mar. 31, 2014

Asset Retirement Obligation Disclosure [Abstract]

Changes to the Company's asset retirement obligation liability

The following table describes the changes to the Company’s asset retirement obligation liability (in thousands):

	Three Months Ended March 31,
	2014			2013
Asset retirement obligation, beginning of period	$	48,536		$	27,260
Liabilities settled	(718		)	(72		)
Accretion expense	791			332
Revisions in estimated cash flows	561			986
Asset retirement obligation, end of period	49,170			28,506
Less: current portion of asset retirement obligation	(3,390		)	(3,845		)
Long-term asset retirement obligation	$	45,780		$	24,661