Revenues Revenues Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended				12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Transportation expenses	$ 49,000	$ 46,000	$ 47,300	$ 49,300	$ 191,587	$ 0	$ 0
Crude oil and natural gas sales					4,678,722	$ 2,982,966	$ 2,026,958
Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales					4,678,722
Transferred over Time
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales					0
North Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales					3,396,625
North Region [Member] | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales					3,396,625
North Region [Member] | Transferred over Time
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales					0
South Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales					1,282,097
South Region [Member] | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales					1,282,097
South Region [Member] | Transferred over Time
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales					0
Crude oil sales
Disaggregation of Revenue [Line Items]
Transportation expenses					162,300
Crude oil and natural gas sales					3,792,594
Crude oil sales | North Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales					3,121,146
Crude oil sales | South Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales					671,448
Natural gas sales
Disaggregation of Revenue [Line Items]
Transportation expenses					29,300
Crude oil and natural gas sales					886,128
Natural gas sales | North Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales					275,479
Natural gas sales | South Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales					610,649
Operated properties | Crude oil sales
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales					2,933,781
Operated properties | Crude oil sales | North Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales					2,330,711
Operated properties | Crude oil sales | South Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales					603,070
Operated properties | Natural gas sales
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales					761,988
Operated properties | Natural gas sales | North Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales					214,741
Operated properties | Natural gas sales | South Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales					547,247
Non-operated properties | Crude oil sales
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales					858,813
Non-operated properties | Crude oil sales | North Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales					790,435
Non-operated properties | Crude oil sales | South Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales					68,378
Non-operated properties | Natural gas sales
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales					124,140
Non-operated properties | Natural gas sales | North Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales					60,738
Non-operated properties | Natural gas sales | South Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales					$ 63,402