Derivative Financial Instruments - Summary of Open Commodity Derivative Contracts (Details) $ in Thousands, bbl in Millions, MMBTU in Millions	6 Months Ended
Jun. 30, 2019 USD ($) MMBTU $ / MMBTU $ / bbl bbl	Dec. 31, 2018 USD ($)
Derivative [Line Items]
Fair Value Asset \| $	$ 58,198	$ 23,374
Fair Value (Liability) \| $	$ (20,692)	$ (62,350)
Commodity Derivative Contract Fixed Price Swaps Two \| Crude Oil
Derivative [Line Items]
Year	2020
Index	NYMEX-WTI
Total Volumes \| MMBTU	0.5
Weighted Average (“WA”) Price per Unit \| $ / MMBTU	60.31
Fair Value Asset \| $	$ 1,727
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 (“WA”) Price per Unit \| $ / MMBTU	2.78
Fair Value Asset \| $	$ 2,979
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 (July through December)
Index	NYMEX-WTI
Total Volumes \| bbl	0.7
Weighted Average (“WA”) Price per Unit \| $ / bbl	59.06
Fair Value Asset \| $	$ 601
Commodity Derivative Contract Fixed Price Swaps One \| Natural Gas
Derivative [Line Items]
Year	2019 (July through December)
Index	NYMEX-Henry Hub
Total Volumes \| MMBTU	90.5
Weighted Average (“WA”) Price per Unit \| $ / MMBTU	2.78
Fair Value Asset \| $	$ 37,790
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 (July through December)
Index	NW Rockies Basis Swap
Total Volumes \| MMBTU	63.5
Weighted Average (“WA”) Price per Unit \| $ / MMBTU	(0.54)
Fair Value (Liability) \| $	$ (13,336)
Commodity Derivative Basis Swap Contracts Two \| Natural Gas
Derivative [Line Items]
Year	2020
Index	NW Rockies Basis Swap
Total Volumes \| MMBTU	11.4
Weighted Average (“WA”) Price per Unit \| $ / MMBTU	(0.17)
Fair Value Asset \| $	$ 1,114
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 (July 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 \| $	$ 1,376
Commodity Derivative Contract Collars Two \| Natural Gas
Derivative [Line Items]
Year	2020
Index	NYMEX
Total Volumes \| MMBTU	76.1
Weighted Average Floor Price \| $ / MMBTU	2.49
Weighted Average Ceiling Price \| $ / MMBTU	2.97
Fair Value Asset \| $	$ 6,127
Commodity Derivative Contract Collars Three \| Natural Gas
Derivative [Line Items]
Year	2021
Index	NYMEX
Total Volumes \| MMBTU	7.2
Weighted Average Floor Price \| $ / MMBTU	2.47
Weighted Average Ceiling Price \| $ / MMBTU	3.03
Fair Value (Liability) \| $	$ (390)
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	27.9
Weighted Average Floor Price \| $ / MMBTU	2.41
Fair Value Asset \| $	$ 1,707

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Derivative maturity period.

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Derivative swap type average differential.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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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.

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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.

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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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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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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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- 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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