Fair Value of Financial Instruments (Schedule of Assets and Liabilities Measured on Non Recurring Basis) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Fair value, liabilities	$ 7,326	$ 599	$ 7,855	$ 1,244
Level 3
Fair value, liabilities	7,326	599	7,855	1,244
Asset Retirement Obligations
Fair value, liabilities	7,326	599	7,855	1,244
Asset Retirement Obligations | Level 3
Fair value, liabilities	$ 7,326	$ 599	$ 7,855	$ 1,244