Property and Equipment (Schedule of Property and Equipment) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Property and Equipment [Abstract]
Proved oil and natural gas properties	$ 2,307,891	$ 1,982,657
Unproved oil and natural gas properties	39,191	36,992
Other	8,137	5,998
Net property and equipment	$ 2,355,219	$ 2,025,647