Segment and Geographic Reporting (Details) (USD $)	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Segment Reporting Information [Line Items]
Oil and natural gas sales	$ 596,191,000		$ 373,286,000		$ 262,629,000
Interest income	1,216,000		1,174,000		1,087,000
DD&A expenses	231,235,000		163,573,000		135,863,000
DD&A - per unit of production (in dollars per unit)	$ 36.39		$ 31.02		$ 29.35
Income (loss) before income taxes	234,247,000		94,406,000		38,295,000
Segment capital expenditures	327,647,000	[1]	177,039,000	[1]	88,124,000	[1]
Total assets by geographical area [Abstract]
Property, plant and equipment	1,044,842,000		727,024,000
Goodwill	102,581,000		102,581,000
Other assets	479,357,000		419,649,000
Total Assets	1,626,780,000		1,249,254,000
Significant Acquisitions and Disposals [Line Items]
Sales to Ecopetrol, as a percentage of total revenue (in hundredths)	87.00%		96.00%		94.00%
Number of significant customers	3
Concentration Risk [Line Items]
Interest expense	1,600,000
Refiner [Member]
Concentration Risk [Line Items]
Sales to significant customers., as a percentage of total revenue (in hundredths)	30.00%		4.00%		6.00%
Shell [Member]
Concentration Risk [Line Items]
Sales to significant customers., as a percentage of total revenue (in hundredths)	3.00%
YPF [Member]
Concentration Risk [Line Items]
Sales to significant customers., as a percentage of total revenue (in hundredths)	2.00%
Santa Victoria Block Farm out interest [Member]
Significant Acquisitions and Disposals [Line Items]
Participating Interest (in hundredths)	50.00%
Colombia [Member]
Segment Reporting Information [Line Items]
Oil and natural gas sales	543,999,000		359,302,000		248,834,000
Interest income	492,000		460,000		466,000
DD&A expenses	141,133,000		133,728,000		127,213,000
DD&A - per unit of production (in dollars per unit)	$ 26.17		$ 26.80		$ 29.64
Income (loss) before income taxes	313,516,000		142,486,000		55,827,000
Segment capital expenditures	202,551,000	[1]	105,482,000	[1]	81,364,000	[1]
Total assets by geographical area [Abstract]
Property, plant and equipment	816,396,000		654,416,000
Goodwill	102,581,000		102,581,000
Other assets	269,843,000		155,798,000
Total Assets	1,188,820,000		912,795,000
Argentina [Member]
Segment Reporting Information [Line Items]
Oil and natural gas sales	48,016,000		13,984,000		13,795,000
Interest income	66,000		26,000		127,000
DD&A expenses	45,506,000		29,416,000		8,339,000
DD&A - per unit of production (in dollars per unit)	$ 49.61		$ 103.56		$ 24.72
Income (loss) before income taxes	(32,635,000)		(27,247,000)		(4,230,000)
Segment capital expenditures	36,289,000	[1]	33,930,000	[1]	4,532,000	[1]
Total assets by geographical area [Abstract]
Property, plant and equipment	129,072,000		29,031,000
Goodwill	0		0
Other assets	34,672,000		15,220,000
Total Assets	163,744,000		44,251,000
Peru [Member]
Segment Reporting Information [Line Items]
Oil and natural gas sales	0		0		0
Interest income	140,000		0		0
DD&A expenses	42,035,000		40,000		0
DD&A - per unit of production (in dollars per unit)	$ 0		$ 0		$ 0
Income (loss) before income taxes	(46,249,000)		(1,430,000)		(396,000)
Segment capital expenditures	36,224,000	[1]	15,029,000	[1]	1,606,000	[1]
Total assets by geographical area [Abstract]
Property, plant and equipment	34,305,000		28,578,000
Goodwill	0		0
Other assets	9,597,000		18,575,000
Total Assets	43,902,000		47,153,000
All Other Segments [Member]
Segment Reporting Information [Line Items]
Oil and natural gas sales	4,176,000		0		0
Interest income	518,000		688,000		494,000
DD&A expenses	2,561,000		389,000		311,000
DD&A - per unit of production (in dollars per unit)	$ 59.48		$ 0		$ 0
Income (loss) before income taxes	(385,000)		(19,403,000)		(12,906,000)
Segment capital expenditures	52,583,000	[1]	22,598,000	[1]	622,000	[1]
Total assets by geographical area [Abstract]
Property, plant and equipment	65,069,000		14,999,000
Goodwill	0		0
Other assets	165,245,000		230,056,000
Total Assets	$ 230,314,000		$ 245,055,000

[1] Net of proceeds from the farm out of a 50% interest in the Santa Victoria Block and the sale of a blow-out preventer in Argentina in 2011 (see Note 6), the Garibay overriding royalty in Colombia in 2010 (see Note 6) and the Guachiria Blocks in Colombia in 2009 (see Note 6