Asset Retirement Obligations (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Changes in the Company's asset retirement obligations
Beginning asset retirement obligations				$ 11,951
Liabilities incurred during period				2,670
Liabilities settled during period				(436)
Revisions in estimated cash flows				(788)
Accretion expense		$ 182	$ 130	427	$ 371
Ending asset retirement obligations		13,824		13,824
Less: current asset retirement obligations	[1]	(411)		(411)
Long-term asset retirement obligations		$ 13,413		$ 13,413		$ 11,640

[1] Included in accrued liabilities in the Company’s unaudited condensed consolidated balance sheet at September 30, 2015.