Revenues Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	$ 1,109,584	$ 1,113,852
Transportation expenses	49,139	49,297
Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	1,109,584	1,113,852
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	826,660	817,598
North Region [Member] | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	826,660	817,598
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	282,924	296,254
South Region [Member] | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	282,924	296,254
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	911,118	906,281
Transportation expenses	41,600	40,400
Crude oil sales | North Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	764,333	752,098
Crude oil sales | South Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	146,785	154,183
Natural gas sales
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	198,466	207,571
Transportation expenses	7,500	8,900
Natural gas sales | North Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	62,327	65,500
Natural gas sales | South Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	136,139	142,071
Operated properties | Crude oil sales
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	722,152	707,664
Operated properties | Crude oil sales | North Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	585,605	569,211
Operated properties | Crude oil sales | South Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	136,547	138,453
Operated properties | Natural gas sales
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	176,159	179,074
Operated properties | Natural gas sales | North Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	51,461	51,820
Operated properties | Natural gas sales | South Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	124,698	127,254
Non-operated properties | Crude oil sales
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	188,966	198,617
Non-operated properties | Crude oil sales | North Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	178,728	182,887
Non-operated properties | Crude oil sales | South Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	10,238	15,730
Non-operated properties | Natural gas sales
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	22,307	28,497
Non-operated properties | Natural gas sales | North Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	10,866	13,680
Non-operated properties | Natural gas sales | South Region [Member]
Disaggregation of Revenue [Line Items]
Crude oil and natural gas sales	$ 11,441	$ 14,817