Property, Plant and Equipment - Summary of Impairment Expense by Project (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Total Impairment	$ 160	$ 4,095
Kingsville Dome Project [Member]
Total Impairment	160	474
Rosita Project [Member]
Total Impairment		2,821
Vasquez Project [Member]
Total Impairment		276
Ambrosia Lake Project [Member]
Total Impairment		512
Other Project [Member]
Total Impairment		$ 12