Fair Value Measurements - Fair Value Measurements - Nonrecurring (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Construction in Progress - Arctic Star Plant
Impairment	$ 10,290
Weathered Lagoon Plant
Impairment	6,151
Oil and Gas Property - Proved
Impairment	1,375
Oil and Gas Property - Unproved
Impairment	314
Level 3 | Construction in Progress - Arctic Star Plant
Fair Value	5,736	8,833
Level 3 | Weathered Lagoon Plant
Fair Value	79	6,236
Level 3 | Oil and Gas Property - Proved
Fair Value	1,633	3,369
Level 3 | Oil and Gas Property - Unproved
Fair Value	$ 77	$ 391