Revenues Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	$ 1,273,238	$ 704,818	$ 3,524,618	$ 1,965,216
Transportation expenses	46,008	$ 0	142,559	$ 0
Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	1,273,238		3,524,618
Transferred over Time
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	0		0
North Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	936,542		2,593,430
North Region [Member] | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	936,542		2,593,430
North Region [Member] | Transferred over Time
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	0		0
South Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	336,696		931,188
South Region [Member] | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	336,696		931,188
South Region [Member] | Transferred over Time
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	0		0
Crude oil sales
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	1,038,558		2,891,722
Transportation expenses	39,300		119,900
Crude oil sales | North Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	859,764		2,395,745
Crude oil sales | South Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	178,794		495,977
Natural gas sales
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	234,680		632,896
Transportation expenses	6,700		22,600
Natural gas sales | North Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	76,778		197,685
Natural gas sales | South Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	157,902		435,211
Operated properties | Crude oil sales
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	793,757		2,234,607
Operated properties | Crude oil sales | North Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	634,251		1,791,045
Operated properties | Crude oil sales | South Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	159,506		443,562
Operated properties | Natural gas sales
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	200,549		542,237
Operated properties | Natural gas sales | North Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	60,381		153,627
Operated properties | Natural gas sales | South Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	140,168		388,610
Non-operated properties | Crude oil sales
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	244,801		657,115
Non-operated properties | Crude oil sales | North Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	225,513		604,700
Non-operated properties | Crude oil sales | South Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	19,288		52,415
Non-operated properties | Natural gas sales
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	34,131		90,659
Non-operated properties | Natural gas sales | North Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	16,397		44,058
Non-operated properties | Natural gas sales | South Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	$ 17,734		$ 46,601