Asset Retirement Obligations (Tables)

12 Months Ended

Dec. 31, 2012

Asset Retirement Obligations [Abstract]

Schedule of changes in Company's asset retirement obligations

	Year ended December 31,
	2012		2011
Beginning asset retirement obligations	$	4,270	$	3,695
Liabilities incurred during period		1,243		187
Revisions in estimated cash flows		–		312
Liabilities settled during period		–		(133	)
Accretion expense		256		209
Ending asset retirement obligations	$	5,769	$	4,270