Price-Risk Management Price-Risk Management (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($) MMBTU $ / MMBTU $ / Boe bbl	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) MMBTU $ / MMBTU $ / Boe bbl	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain (Loss) on Price Risk Derivatives, Net | $	$ (13,600)	$ (1,600)	$ (30,700)	$ 14,500
Cash Received (Paid) On Settlements of Derivative Contracts | $			(5,671)	$ (2,503)
Receivables for Settled Derivatives | $	0		0		$ 2,200
Payables for Settled Derivatives | $	2,400		2,400		400
Derivative, Fair Value, Net | $	(21,100)		(21,100)		(100)
Other Current Assets [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative Asset, Fair Value, Gross Asset | $	2,600		2,600		5,100
Other Noncurrent Assets [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative Asset, Fair Value, Gross Asset | $	2,600		2,600		2,600
Other Current Liabilities [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative Liability, Fair Value, Gross Liability | $	17,900		17,900		5,100
Other Noncurrent Liabilities [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative Liability, Fair Value, Gross Liability | $	$ 8,400		$ 8,400		$ 2,800
Swap [Member] | Oil Derivative Swaps [Member] | Fourth Quarter 2018 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Portion of Future Oil and Gas Production Being Hedged | bbl	122,800		122,800
Derivative, Swap Type, Fixed Price | $ / Boe	52.23		52.23
Swap [Member] | Oil Derivative Swaps [Member] | First Quarter 2019 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Portion of Future Oil and Gas Production Being Hedged | bbl	116,700		116,700
Derivative, Swap Type, Fixed Price | $ / Boe	53.75		53.75
Swap [Member] | Oil Derivative Swaps [Member] | Second Quarter 2019 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Portion of Future Oil and Gas Production Being Hedged | bbl	112,200		112,200
Derivative, Swap Type, Fixed Price | $ / Boe	53.74		53.74
Swap [Member] | Oil Derivative Swaps [Member] | Third Quarter 2019 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Portion of Future Oil and Gas Production Being Hedged | bbl	108,000		108,000
Derivative, Swap Type, Fixed Price | $ / Boe	53.85		53.85
Swap [Member] | Oil Derivative Swaps [Member] | Fourth Quarter 2019 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Portion of Future Oil and Gas Production Being Hedged | bbl	104,000		104,000
Derivative, Swap Type, Fixed Price | $ / Boe	53.83		53.83
Swap [Member] | Oil Derivative Swaps [Member] | First Quarter 2020 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Portion of Future Oil and Gas Production Being Hedged | bbl	81,300		81,300
Derivative, Swap Type, Fixed Price | $ / Boe	52.42		52.42
Swap [Member] | Oil Derivative Swaps [Member] | Second Quarter 2020 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Portion of Future Oil and Gas Production Being Hedged | bbl	77,850		77,850
Derivative, Swap Type, Fixed Price | $ / Boe	52.38		52.38
Swap [Member] | Oil Derivative Swaps [Member] | Third Quarter 2020 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Portion of Future Oil and Gas Production Being Hedged | bbl	74,700		74,700
Derivative, Swap Type, Fixed Price | $ / Boe	52.34		52.34
Swap [Member] | Oil Derivative Swaps [Member] | Fourth Quarter 2020 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Portion of Future Oil and Gas Production Being Hedged | bbl	72,000		72,000
Derivative, Swap Type, Fixed Price | $ / Boe	52.29		52.29
Swap [Member] | Natural Gas Derivative Swaps [Member] | Fourth Quarter 2018 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Swap Type, Fixed Price	2.96		2.96
Future Gas Production Hedged in MMBtu (Energy Item Type) | MMBTU	8,273,000		8,273,000
Swap [Member] | Natural Gas Derivative Swaps [Member] | First Quarter 2019 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Swap Type, Fixed Price	3.08		3.08
Future Gas Production Hedged in MMBtu (Energy Item Type) | MMBTU	7,516,000		7,516,000
Swap [Member] | Natural Gas Derivative Swaps [Member] | Second Quarter 2019 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Swap Type, Fixed Price	2.83		2.83
Future Gas Production Hedged in MMBtu (Energy Item Type) | MMBTU	6,060,000		6,060,000
Swap [Member] | Natural Gas Derivative Swaps [Member] | Third Quarter 2019 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Swap Type, Fixed Price	2.84		2.84
Future Gas Production Hedged in MMBtu (Energy Item Type) | MMBTU	5,550,000		5,550,000
Swap [Member] | Natural Gas Derivative Swaps [Member] | Fourth Quarter 2019 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Swap Type, Fixed Price	2.84		2.84
Future Gas Production Hedged in MMBtu (Energy Item Type) | MMBTU	5,966,000		5,966,000
Swap [Member] | Natural Gas Derivative Swaps [Member] | First Quarter 2020 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Swap Type, Fixed Price	2.83		2.83
Future Gas Production Hedged in MMBtu (Energy Item Type) | MMBTU	5,370,000		5,370,000
Swap [Member] | Natural Gas Derivative Swaps [Member] | Second Quarter 2020 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Swap Type, Fixed Price	2.76		2.76
Future Gas Production Hedged in MMBtu (Energy Item Type) | MMBTU	3,688,000		3,688,000
Swap [Member] | Natural Gas Derivative Swaps [Member] | Third Quarter 2020 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Swap Type, Fixed Price	2.76		2.76
Future Gas Production Hedged in MMBtu (Energy Item Type) | MMBTU	3,585,000		3,585,000
Swap [Member] | Natural Gas Derivative Swaps [Member] | Fourth Quarter 2020 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Swap Type, Fixed Price	2.77		2.77
Future Gas Production Hedged in MMBtu (Energy Item Type) | MMBTU	3,362,000		3,362,000
Swap [Member] | Natural Gas Liquid Derivative [Member] | Fourth Quarter 2018 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Swap Type, Fixed Price	24.79		24.79
Future NGL Production Hedged in Bbls (Energy Item Type) | bbl	148,200		148,200
Swap [Member] | Natural Gas Liquid Derivative [Member] | First Quarter 2019 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Swap Type, Fixed Price	27.05		27.05
Future NGL Production Hedged in Bbls (Energy Item Type) | bbl	150,000		150,000
Swap [Member] | Natural Gas Liquid Derivative [Member] | Second Quarter 2019 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Swap Type, Fixed Price	27.05		27.05
Future NGL Production Hedged in Bbls (Energy Item Type) | bbl	150,000		150,000
Swap [Member] | Natural Gas Liquid Derivative [Member] | Third Quarter 2019 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Swap Type, Fixed Price	27.05		27.05
Future NGL Production Hedged in Bbls (Energy Item Type) | bbl	150,000		150,000
Swap [Member] | Natural Gas Liquid Derivative [Member] | Fourth Quarter 2019 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Swap Type, Fixed Price	27.05		27.05
Future NGL Production Hedged in Bbls (Energy Item Type) | bbl	150,000		150,000
Basis Swap [Member] | Natural Gas Basis Derivative Swaps [Member] | Fourth Quarter 2018 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Future Gas Production Hedged in MMBtu (Energy Item Type) | MMBTU	8,000,000		8,000,000
Derivative, Basis Swap Type, Fixed Price	(0.07)		(0.07)
Basis Swap [Member] | Natural Gas Basis Derivative Swaps [Member] | First Quarter 2019 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Future Gas Production Hedged in MMBtu (Energy Item Type) | MMBTU	11,310,000		11,310,000
Derivative, Basis Swap Type, Fixed Price	(0.08)		(0.08)
Basis Swap [Member] | Natural Gas Basis Derivative Swaps [Member] | Second Quarter 2019 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Future Gas Production Hedged in MMBtu (Energy Item Type) | MMBTU	11,975,000		11,975,000
Derivative, Basis Swap Type, Fixed Price	0.04		0.04
Basis Swap [Member] | Natural Gas Basis Derivative Swaps [Member] | Third Quarter 2019 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Future Gas Production Hedged in MMBtu (Energy Item Type) | MMBTU	12,095,000		12,095,000
Derivative, Basis Swap Type, Fixed Price	0.03		0.03
Basis Swap [Member] | Natural Gas Basis Derivative Swaps [Member] | Fourth Quarter 2019 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Future Gas Production Hedged in MMBtu (Energy Item Type) | MMBTU	12,095,000		12,095,000
Derivative, Basis Swap Type, Fixed Price	(0.04)		(0.04)
Basis Swap [Member] | Natural Gas Basis Derivative Swaps [Member] | First Quarter 2020 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Future Gas Production Hedged in MMBtu (Energy Item Type) | MMBTU	6,279,000		6,279,000
Derivative, Basis Swap Type, Fixed Price	(0.08)		(0.08)
Basis Swap [Member] | Natural Gas Basis Derivative Swaps [Member] | Second Quarter 2020 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Future Gas Production Hedged in MMBtu (Energy Item Type) | MMBTU	6,279,000		6,279,000
Derivative, Basis Swap Type, Fixed Price	(0.08)		(0.08)
Basis Swap [Member] | Natural Gas Basis Derivative Swaps [Member] | Third Quarter 2020 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Future Gas Production Hedged in MMBtu (Energy Item Type) | MMBTU	6,348,000		6,348,000
Derivative, Basis Swap Type, Fixed Price	(0.07)		(0.07)
Basis Swap [Member] | Natural Gas Basis Derivative Swaps [Member] | Fourth Quarter 2020 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Future Gas Production Hedged in MMBtu (Energy Item Type) | MMBTU	6,348,000		6,348,000
Derivative, Basis Swap Type, Fixed Price	(0.08)		(0.08)
Basis Swap [Member] | Oil Basis Derivative [Member] | Fourth Quarter 2018 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Portion of Future Oil and Gas Production Being Hedged | bbl	80,000		80,000
Derivative, Basis Swap Type, Fixed Price	4.13		4.13
Basis Swap [Member] | Oil Basis Derivative [Member] | First Quarter 2019 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Portion of Future Oil and Gas Production Being Hedged | bbl	45,000		45,000
Derivative, Basis Swap Type, Fixed Price	4.65		4.65
Basis Swap [Member] | Oil Basis Derivative [Member] | Second Quarter 2019 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Portion of Future Oil and Gas Production Being Hedged | bbl	45,000		45,000
Derivative, Basis Swap Type, Fixed Price	4.65		4.65
Basis Swap [Member] | Oil Basis Derivative [Member] | Third Quarter 2019 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Portion of Future Oil and Gas Production Being Hedged | bbl	45,000		45,000
Derivative, Basis Swap Type, Fixed Price	4.65		4.65
Basis Swap [Member] | Oil Basis Derivative [Member] | Fourth Quarter 2019 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Portion of Future Oil and Gas Production Being Hedged | bbl	45,000		45,000
Derivative, Basis Swap Type, Fixed Price	4.65		4.65