Derivative Activities (Narrative) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Derivative [Line Items]
Accrued and other liabilities	$ 78,966	$ 79,045
Other non-current liabilities	12,462	12,911
Commodity Contract [Member] | Oil And Natural Gas [Member]
Derivative [Line Items]
Accrued and other liabilities	100	0
Other non-current liabilities	$ 5,000	$ 5,000