Revenues Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	$ 1,081,400	$ 1,273,238	$ 3,328,409	$ 3,524,618
Transportation expenses	62,038	46,008	164,569	142,559
Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	1,081,400	1,273,238	3,328,409	3,524,618
Transferred over Time
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	0	0	0	0
North Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	779,899	936,542	2,449,485	2,593,430
North Region [Member] | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	779,899	936,542	2,449,485	2,593,430
North Region [Member] | Transferred over Time
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	0	0	0	0
South Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	301,501	336,696	878,924	931,188
South Region [Member] | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	301,501	336,696	878,924	931,188
South Region [Member] | Transferred over Time
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	0	0	0	0
Crude oil sales
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	989,297	1,038,558	2,905,561	2,891,722
Transportation expenses	53,000	39,300	140,700	119,900
Crude oil sales | North Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	766,112	859,764	2,346,669	2,395,745
Crude oil sales | South Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	223,185	178,794	558,892	495,977
Natural gas sales
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	92,103	234,680	422,848	632,896
Transportation expenses	9,000	6,700	23,900	22,600
Natural gas sales | North Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	13,787	76,778	102,816	197,685
Natural gas sales | South Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	78,316	157,902	320,032	435,211
Operated properties | Crude oil sales
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	804,580	793,757	2,311,260	2,234,607
Operated properties | Crude oil sales | North Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	593,729	634,251	1,787,776	1,791,045
Operated properties | Crude oil sales | South Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	210,851	159,506	523,484	443,562
Operated properties | Natural gas sales
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	82,089	200,549	374,611	542,237
Operated properties | Natural gas sales | North Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	10,719	60,381	83,831	153,627
Operated properties | Natural gas sales | South Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	71,370	140,168	290,780	388,610
Non-operated properties | Crude oil sales
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	184,717	244,801	594,301	657,115
Non-operated properties | Crude oil sales | North Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	172,383	225,513	558,893	604,700
Non-operated properties | Crude oil sales | South Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	12,334	19,288	35,408	52,415
Non-operated properties | Natural gas sales
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	10,014	34,131	48,237	90,659
Non-operated properties | Natural gas sales | North Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	3,068	16,397	18,985	44,058
Non-operated properties | Natural gas sales | South Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	$ 6,946	$ 17,734	$ 29,252	$ 46,601