Leases (Summary of Lease Related Expenses) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Lessee, Lease, Description [Line Items]
Interest on lease liabilities	$ 86	$ 92	$ 172	$ 188
Sublease income	(662)	(336)	(958)	(642)
Net lease expense	89,073	89,636	154,854	199,392
Variable lease expense	8,200	6,000	13,500	12,300
Lease operating expense	126,413	144,644	273,577	353,792
Property, plant and equipment
Lessee, Lease, Description [Line Items]
Operating lease	26,738	13,104	31,634	37,660
Lease operating expense	10,000	7,500	14,900	22,900
Lease operating expenses
Lessee, Lease, Description [Line Items]
Operating lease	48,049	53,588	94,133	125,189
Lease operating expense	11,100	21,400	23,500	54,300
Transportation, gathering and processing
Lessee, Lease, Description [Line Items]
Operating lease	9,982	9,137	19,758	19,063
Lease operating expense	7,600	6,600	14,900	8,000
Selling and general expense
Lessee, Lease, Description [Line Items]
Operating lease	2,453	3,281	5,273	6,750
Lease operating expense	500	1,000	1,300	2,200
Other operating expense
Lessee, Lease, Description [Line Items]
Operating lease	2,427	4,201	4,842	4,615
Lease operating expense				2,400
Impairment of assets
Lessee, Lease, Description [Line Items]
Operating lease	$ 0	$ 6,555	$ 0	$ 6,555