Segment and Geographic Reporting (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011		Dec. 31, 2011
Segment Reporting Information [Line Items]
Oil and natural gas sales	$ 168,616	$ 150,824	$ 438,406	$ 434,784
Interest income	317	209	1,628	888
Depletion, depreciation, accretion and impairment	45,044	49,852	137,982	160,174
Depletion, depreciation, accretion and impairment - per unit of production (in dollars per unit)	25.12	29.50	29.98	34.45
Income (loss) before income taxes	76,013	79,059	139,676	179,028
Segment capital expenditures	61,790	58,563	215,985	229,155	[1]
Total assets by geographical area [Abstract]
Property, plant and equipment	1,118,890		1,118,890			1,044,842
Goodwill	102,581		102,581			102,581
Other assets	401,558		401,558			479,357
Total Assets	1,623,029		1,623,029			1,626,780
Colombia [Member]
Segment Reporting Information [Line Items]
Oil and natural gas sales	145,610	133,475	376,261	399,252
Interest income	171	130	598	375
Depletion, depreciation, accretion and impairment	35,255	34,915	90,625	104,560
Depletion, depreciation, accretion and impairment - per unit of production (in dollars per unit)	24.46	25.53	24.96	26.33
Income (loss) before income taxes	79,915	96,503	182,516	228,118
Segment capital expenditures	35,880	40,100	98,476	136,580	[1]
Total assets by geographical area [Abstract]
Property, plant and equipment	819,820		819,820			816,396
Goodwill	102,581		102,581			102,581
Other assets	243,124		243,124			269,843
Total Assets	1,165,525		1,165,525			1,188,820
Argentina [Member]
Segment Reporting Information [Line Items]
Oil and natural gas sales	22,332	15,189	59,183	33,038
Interest income	10	(22)	96	6
Depletion, depreciation, accretion and impairment	9,165	6,509	23,080	13,161
Depletion, depreciation, accretion and impairment - per unit of production (in dollars per unit)	26.60	21.62	24.54	20.12
Income (loss) before income taxes	1,777	(1,623)	2,568	(5,152)
Segment capital expenditures	11,568	7,099	28,412	25,859	[1]
Total assets by geographical area [Abstract]
Property, plant and equipment	134,786		134,786			129,072
Goodwill	0		0			0
Other assets	46,383		46,383			34,672
Total Assets	181,169		181,169			163,744
Peru [Member]
Segment Reporting Information [Line Items]
Oil and natural gas sales	0	0	0	0
Interest income	0	6	15	140
Depletion, depreciation, accretion and impairment	68	7,375	1,174	40,838
Depletion, depreciation, accretion and impairment - per unit of production (in dollars per unit)	0.00	0.00	0.00	0.00
Income (loss) before income taxes	(847)	(8,432)	(4,147)	(43,428)
Segment capital expenditures	11,204	4,096	43,866	29,670	[1]
Total assets by geographical area [Abstract]
Property, plant and equipment	76,996		76,996			34,305
Goodwill	0		0			0
Other assets	12,416		12,416			9,597
Total Assets	89,412		89,412			43,902
Brazil [Member]
Segment Reporting Information [Line Items]
Oil and natural gas sales	674	2,160	2,962	2,494
Interest income	40	8	607	19
Depletion, depreciation, accretion and impairment	305	830	22,379	1,082
Depletion, depreciation, accretion and impairment - per unit of production (in dollars per unit)	40.35	38.74	708.76	42.54
Income (loss) before income taxes	(1,170)	(592)	(24,467)	(3,336)
Segment capital expenditures	2,838	7,013	44,536	35,687	[1]
Total assets by geographical area [Abstract]
Property, plant and equipment	84,124		84,124			61,875
Goodwill	0		0			0
Other assets	11,467		11,467			17,065
Total Assets	95,591		95,591			78,940
All Other [Member]
Segment Reporting Information [Line Items]
Oil and natural gas sales	0	0	0	0
Interest income	96	87	312	348
Depletion, depreciation, accretion and impairment	251	223	724	533
Depletion, depreciation, accretion and impairment - per unit of production (in dollars per unit)	0.00	0.00	0.00	0.00
Income (loss) before income taxes	(3,662)	(6,797)	(16,794)	2,826
Segment capital expenditures	300	255	695	1,359	[1]
Total assets by geographical area [Abstract]
Property, plant and equipment	3,164		3,164			3,194
Goodwill	0		0			0
Other assets	88,168		88,168			148,180
Total Assets	$ 91,332		$ 91,332			$ 151,374
Argentina [Member]
Segment Reporting Information [Line Items]
Participating Interest (in hundredths)			50.00%
Petrolifera [Member]
Segment Reporting Information [Line Items]
Business acquisition effective date of acquisition			Mar. 18, 2011

[1] Net of proceeds from the farmout of a 50% working interest in the Santa Victoria Block in Argentina in March 2011 (Note 5).