Business Combinations (Narrative) (Details) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended	3 Months Ended	4 Months Ended	9 Months Ended		0 Months Ended	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Sep. 30, 2013 Acquisition Field Revenue [Member]	Sep. 30, 2012 Acquisition Field Revenue [Member]	Sep. 30, 2013 Acquisition Field Revenue [Member]	Sep. 30, 2013 COP Acquisition [Member]	May 31, 2012 Alba Field [Member]	Sep. 30, 2013 Alba Field [Member]
Business Acquisition [Line Items]
Acquisition date									Dec. 23, 2011
Effective date of acquisition											May 31, 2012
Interest acquired, percentage											23.43%
Interest percentage in entity											25.68%
Cash paid										$ 229,577,000
Acquisition field revenue	36,901,000	83,275,000	220,738,000	121,444,000			62,100,000	116,200,000
Acquisition income from operations	(7,998,000)	19,101,000	31,479,000	(17,956,000)		(18,700,000)	600,000	(3,700,000)
Deposit amount					$ 10,000,000