Commitments and Contingencies Commitments and Contigencies (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) MMcf bbl MBbls
Supply Commitment
Dollar Commitment ($ in thousands) | $	$ 458,927
Appalachiain Basin
Supply Commitment
Oil and Gas Delivery Commitments Volumes (MMcf)	31,165
Wattenberg Field
Supply Commitment
Oil and Gas Delivery Commitments Volumes (MMcf)	211,532
Delaware Basin [Member]
Supply Commitment
Oil and Gas Delivery Commitments Volumes (MMcf)	62,120
First Year Commitment [Member]
Supply Commitment
Dollar Commitment ($ in thousands) | $	$ 64,690
First Year Commitment [Member] | Appalachiain Basin
Supply Commitment
Oil and Gas Delivery Commitments Volumes (MMcf)	7,117
First Year Commitment [Member] | Wattenberg Field
Supply Commitment
Oil and Gas Delivery Commitments Volumes (MMcf)	7,416
First Year Commitment [Member] | Delaware Basin [Member]
Supply Commitment
Oil and Gas Delivery Commitments Volumes (MMcf)	25,520
Second Year Commitment [Member]
Supply Commitment
Dollar Commitment ($ in thousands) | $	$ 99,560
Second Year Commitment [Member] | Appalachiain Basin
Supply Commitment
Oil and Gas Delivery Commitments Volumes (MMcf)	7,136
Second Year Commitment [Member] | Wattenberg Field
Supply Commitment
Oil and Gas Delivery Commitments Volumes (MMcf)	27,794
Second Year Commitment [Member] | Delaware Basin [Member]
Supply Commitment
Oil and Gas Delivery Commitments Volumes (MMcf)	25,600
Third Year Commitment [Member]
Supply Commitment
Dollar Commitment ($ in thousands) | $	$ 69,434
Third Year Commitment [Member] | Appalachiain Basin
Supply Commitment
Oil and Gas Delivery Commitments Volumes (MMcf)	7,117
Third Year Commitment [Member] | Wattenberg Field
Supply Commitment
Oil and Gas Delivery Commitments Volumes (MMcf)	31,025
Third Year Commitment [Member] | Delaware Basin [Member]
Supply Commitment
Oil and Gas Delivery Commitments Volumes (MMcf)	11,000
Fourth Year Commitment [Member]
Supply Commitment
Dollar Commitment ($ in thousands) | $	$ 65,060
Fourth Year Commitment [Member] | Appalachiain Basin
Supply Commitment
Oil and Gas Delivery Commitments Volumes (MMcf)	6,965
Fourth Year Commitment [Member] | Wattenberg Field
Supply Commitment
Oil and Gas Delivery Commitments Volumes (MMcf)	31,025
Fourth Year Commitment [Member] | Delaware Basin [Member]
Supply Commitment
Oil and Gas Delivery Commitments Volumes (MMcf)	0
commitments 5 years and beyond [Member]
Supply Commitment
Dollar Commitment ($ in thousands) | $	$ 160,183
commitments 5 years and beyond [Member] | Appalachiain Basin
Supply Commitment
Oil and Gas Delivery Commitments Volumes (MMcf)	2,830
commitments 5 years and beyond [Member] | Wattenberg Field
Supply Commitment
Oil and Gas Delivery Commitments Volumes (MMcf)	114,272
commitments 5 years and beyond [Member] | Delaware Basin [Member]
Supply Commitment
Oil and Gas Delivery Commitments Volumes (MMcf)	0
Supply Contract Expiration Date [Member] | Appalachiain Basin
Supply Commitment
Supply Commitments Contract Expiration Date	Aug. 31, 2022
Supply Contract Expiration Date [Member] | Wattenberg Field
Supply Commitment
Supply Commitments Contract Expiration Date	Apr. 30, 2026
Supply Contract Expiration Date [Member] | Delaware Basin [Member]
Supply Commitment
Supply Commitments Contract Expiration Date	Dec. 31, 2020
Crude Oil [Member] | Wattenberg Field
Supply Commitment
Oil and Gas Delivery Commitments Volumes (MMcf) | MBbls	30,085
Crude Oil [Member] | Delaware Basin [Member]
Supply Commitment
Oil and Gas Delivery Commitments Volumes (MMcf) | MBbls	42,772
Crude Oil [Member] | First Year Commitment [Member] | Wattenberg Field
Supply Commitment
Oil and Gas Delivery Commitments Volumes (MMcf) | MBbls	7,438
Crude Oil [Member] | First Year Commitment [Member] | Delaware Basin [Member]
Supply Commitment
Oil and Gas Delivery Commitments Volumes (MMcf) | MBbls	4,493
Crude Oil [Member] | Second Year Commitment [Member] | Wattenberg Field
Supply Commitment
Oil and Gas Delivery Commitments Volumes (MMcf) | MBbls	8,062
Crude Oil [Member] | Second Year Commitment [Member] | Delaware Basin [Member]
Supply Commitment
Oil and Gas Delivery Commitments Volumes (MMcf) | MBbls	8,227
Crude Oil [Member] | Third Year Commitment [Member] | Wattenberg Field
Supply Commitment
Oil and Gas Delivery Commitments Volumes (MMcf) | MBbls	5,085
Crude Oil [Member] | Third Year Commitment [Member] | Delaware Basin [Member]
Supply Commitment
Oil and Gas Delivery Commitments Volumes (MMcf) | MBbls	8,580
Crude Oil [Member] | Fourth Year Commitment [Member] | Wattenberg Field
Supply Commitment
Oil and Gas Delivery Commitments Volumes (MMcf) | MBbls	4,563
Crude Oil [Member] | Fourth Year Commitment [Member] | Delaware Basin [Member]
Supply Commitment
Oil and Gas Delivery Commitments Volumes (MMcf) | MBbls	7,392
Crude Oil [Member] | commitments 5 years and beyond [Member] | Wattenberg Field
Supply Commitment
Oil and Gas Delivery Commitments Volumes (MMcf) | MBbls	4,937
Crude Oil [Member] | commitments 5 years and beyond [Member] | Delaware Basin [Member]
Supply Commitment
Oil and Gas Delivery Commitments Volumes (MMcf) | MBbls	14,080
Crude Oil [Member] | Supply Contract Expiration Date [Member] | Wattenberg Field
Supply Commitment
Supply Commitments Contract Expiration Date	Apr. 30, 2023
Crude Oil [Member] | Supply Contract Expiration Date [Member] | Delaware Basin [Member]
Supply Commitment
Supply Commitments Contract Expiration Date	Dec. 31, 2023
First facilities agreement with midstream provider [Member]
Supply Commitment
incremental volume commitment	51.5
Second facilities agreement with midstream provider [Member]
Supply Commitment
incremental volume commitment	33.5
Wattenberg Field
Supply Commitment
Committed Barrels of Crude Oil per day | bbl	12,500
Natural Gas [Member]
Supply Commitment
Oil and Gas Delivery Commitments Volumes (MMcf)	304,817
Natural Gas [Member] | First Year Commitment [Member]
Supply Commitment
Oil and Gas Delivery Commitments Volumes (MMcf)	40,053
Natural Gas [Member] | Second Year Commitment [Member]
Supply Commitment
Oil and Gas Delivery Commitments Volumes (MMcf)	60,530
Natural Gas [Member] | Third Year Commitment [Member]
Supply Commitment
Oil and Gas Delivery Commitments Volumes (MMcf)	49,142
Natural Gas [Member] | Fourth Year Commitment [Member]
Supply Commitment
Oil and Gas Delivery Commitments Volumes (MMcf)	37,990
Natural Gas [Member] | commitments 5 years and beyond [Member]
Supply Commitment
Oil and Gas Delivery Commitments Volumes (MMcf)	117,102
Crude Oil [Member]
Supply Commitment
Oil and Gas Delivery Commitments Volumes (MMcf)	72,857
Crude Oil [Member] | First Year Commitment [Member]
Supply Commitment
Oil and Gas Delivery Commitments Volumes (MMcf)	11,931
Crude Oil [Member] | Second Year Commitment [Member]
Supply Commitment
Oil and Gas Delivery Commitments Volumes (MMcf)	16,289
Crude Oil [Member] | Third Year Commitment [Member]
Supply Commitment
Oil and Gas Delivery Commitments Volumes (MMcf)	13,665
Crude Oil [Member] | Fourth Year Commitment [Member]
Supply Commitment
Oil and Gas Delivery Commitments Volumes (MMcf)	11,955
Crude Oil [Member] | commitments 5 years and beyond [Member]
Supply Commitment
Oil and Gas Delivery Commitments Volumes (MMcf)	19,017
Minimum [Member] | Delaware Basin [Member]
Supply Commitment
Committed Barrels of Crude Oil per day | bbl	11,400
Maximum [Member] | Delaware Basin [Member]
Supply Commitment
Committed Barrels of Crude Oil per day | bbl	26,400