Impairment of Property and Equipment (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014 method	Mar. 31, 2013
Property, Plant and Equipment Impairment or Disposal [Abstract]
Number of methods to determine fair value of impaired property	3
Impairment of property and equipment	$ 3,406	$ 69,537
Provisions for impairment of unproved properties	$ 3,500	$ 61