Asset Retirement Obligations (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended			9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013	Sep. 30, 2014		Sep. 30, 2013	Dec. 31, 2013
Changes in the Company's asset retirement obligations
Beginning asset retirement obligations				$ 7,484
Liabilities incurred during period				1,906
Liabilities settled during period				(22)
Revisions in estimated cash flows				1,552
Accretion expense	130		86	371		248
Ending asset retirement obligations	11,291			11,291
Less: current asset retirement obligations	(540)	[1]		(540)	[1]
Long-term asset retirement obligations	$ 10,751			$ 10,751			$ 7,309

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