Derivative Financial Instruments - Summary of Open Commodity Derivative Contracts (Details) $ in Thousands, bbl in Millions, MMBTU in Millions	3 Months Ended
Mar. 31, 2019 USD ($) MMBTU $ / MMBTU $ / bbl bbl	Dec. 31, 2018 USD ($)
Derivative [Line Items]
Fair Value Asset	$ 10,985	$ 23,374
Fair Value (Liability)	$ (38,483)	$ (62,350)
Commodity Derivative Contract Fixed Price Swaps Two \| Crude Oil
Derivative [Line Items]
Year	2020
Index	NYMEX-WTI
Total Volumes \| MMBTU	0.1
Weighted Average Price per Unit \| $ / MMBTU	60.05
Fair Value Asset	$ 51
Commodity Derivative Contract Fixed Price Swaps Two \| Natural Gas
Derivative [Line Items]
Year	2020
Index	NYMEX-Henry Hub
Total Volumes \| MMBTU	24.6
Weighted Average Price per Unit \| $ / MMBTU	2.78
Fair Value (Liability)	$ (5,439)
Commodity Derivative Contract Fixed Price Swaps \| Crude Oil
Derivative [Line Items]
Type	Crude oil fixed price swaps
Commodity Derivative Contract Fixed Price Swaps \| Natural Gas
Derivative [Line Items]
Type	Natural gas fixed price swaps
Commodity Derivative Contract Fixed Price Swaps One \| Crude Oil
Derivative [Line Items]
Year	2019 (April through December)
Index	NYMEX-WTI
Total Volumes \| bbl	1.0
Weighted Average Price per Unit \| $ / bbl	58.64
Fair Value (Liability)	$ (1,680)
Commodity Derivative Contract Fixed Price Swaps One \| Natural Gas
Derivative [Line Items]
Year	2019 (April through December)
Index	NYMEX-Henry Hub
Total Volumes \| MMBTU	137.8
Weighted Average Price per Unit \| $ / MMBTU	2.77
Fair Value (Liability)	$ (2,079)
Commodity Derivative Basis Swap Contracts \| Natural Gas
Derivative [Line Items]
Type	Natural gas basis swaps
Commodity Derivative Basis Swap Contracts One \| Natural Gas
Derivative [Line Items]
Year	2019 (April through December)
Index	NW Rockies Basis Swap
Total Volumes \| MMBTU	90.2
Weighted Average Price per Unit \| $ / MMBTU	0.58
Fair Value (Liability)	$ (18,734)
Commodity Derivative Basis Swap Contracts Two \| Natural Gas
Derivative [Line Items]
Year	2020
Index	NW Rockies Basis Swap
Total Volumes \| MMBTU	7.7
Weighted Average Price per Unit \| $ / MMBTU	0.15
Fair Value Asset	$ 770
Commodity Derivative Contract Collars \| Natural Gas
Derivative [Line Items]
Type	Natural gas collars
Commodity Derivative Contract Collars One \| Natural Gas
Derivative [Line Items]
Year	2019 (April through December)
Index	NYMEX
Total Volumes \| MMBTU	2.8
Weighted Average Floor Price \| $ / MMBTU	2.85
Weighted Average Ceiling Price \| $ / MMBTU	3.13
Fair Value Asset	$ 264
Commodity Derivative Contract Collars Two \| Natural Gas
Derivative [Line Items]
Year	2020
Index	NYMEX
Total Volumes \| MMBTU	49.4
Weighted Average Floor Price \| $ / MMBTU	2.51
Weighted Average Ceiling Price \| $ / MMBTU	2.97
Fair Value (Liability)	$ (1,298)
Commodity Derivative Contract Deferred Premium Put Options \| Natural Gas
Derivative [Line Items]
Type	Natural gas deferred premium put options
Commodity Derivative Contract Deferred Premium Put Options One \| Natural Gas
Derivative [Line Items]
Year	2020
Index	NYMEX
Total Volumes \| MMBTU	25.1
Weighted Average Floor Price \| $ / MMBTU	2.41
Fair Value (Liability)	$ (394)

Derivative contract maturity peiod.

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Derivative maturity period.

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- Definition

Derivative swap type average differential.

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No definition available.

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, expected to be settled within one year or normal operating cycle, if longer. Includes assets not subject to a master netting arrangement and not elected to be offset.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Topic 210
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-Section 50
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- Definition

The average cap rate on a group of price risk derivatives such as caps or collars. A payment or receipt is triggered if the market rate exceeds the cap rate on the contract.

+ References

No definition available.

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The average floor rate on a group of price risk derivatives such as floors or collars. A payment or receipt is triggered if the market rate falls below the floor rate on the contract.

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Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, expected to be settled within one year or normal operating cycle, if longer. Includes assets not subject to a master netting arrangement and not elected to be offset.

+ References

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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- Definition

Nominal energy measure used to calculate payments on a derivative instrument.

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Nominal volume used to calculate payments on a derivative instrument.

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No definition available.

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- Definition

Indicates whether the entity pays a variable or fixed price on a price risk swap.

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Average fixed price related to the group of price risk swap derivatives.

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No definition available.

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- Definition

Reference to the index or unit of measurement for the underlying which establishes the pricing terms of the derivative instrument. For example, the basis on the underlying for a natural gas futures contract might be the NYMEX price per million British thermal units (MMBtu).

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No definition available.

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