Fair Value Measurements (Details 1) (Fair value on a non-recurring basis, USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Assets (Liabilities)
Total	$ (1,701)	$ (3,985)
Asset retirement obligations
Assets (Liabilities)
Asset retirement obligations	(1,701)	(3,985)
Level 1 | Asset retirement obligations
Assets (Liabilities)
Asset retirement obligations	0	0
Level 2 | Asset retirement obligations
Assets (Liabilities)
Asset retirement obligations	0	0
Level 3
Assets (Liabilities)
Total	(1,701)	(3,985)
Level 3 | Asset retirement obligations
Assets (Liabilities)
Asset retirement obligations	$ (1,701)	$ (3,985)