Asset Retirement Obligations - Summary of Asset Retirement Obligation (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Asset Retirement Obligation Disclosure [Abstract]
Balance, beginning of period			$ 4,196	$ 3,834	$ 3,834
Changes in cash flow estimates					136
Costs incurred			$ (88)		(199)
Accretion expense	$ 113	$ 22	225	$ 102	425
Balance, end of period	4,333		4,333		4,196
Less: Current portion	(144)		(144)		(196)
Non-current Portion	$ 4,189		$ 4,189		$ 4,000