Asset Retirement Obligations (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended			6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013	Jun. 30, 2014		Jun. 30, 2013	Dec. 31, 2013
Changes in the Company's asset retirement obligations
Beginning asset retirement obligations				$ 7,484
Liabilities incurred during period				838
Liabilities settled during period				(22)
Revisions in estimated cash flows				1,659
Accretion expense	123		80	241		161
Ending asset retirement obligations	10,200			10,200
Less: current asset retirement obligations	(477)	[1]		(477)	[1]
Long-term asset retirement obligations	$ 9,723			$ 9,723			$ 7,309

[1] Included in accrued liabilities in the Company’s unaudited condensed consolidated balance sheet at June 30, 2014.