Derivatives (Derivatives Not Designated as Hedging Instruments - Commodity Contracts) (Details) MMBTU in Thousands, Boe in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) MMBTU Boe	Dec. 31, 2018 USD ($) MMBTU Boe
Derivative [Line Items]
Derivative assets - Fair value	$ 330,316	$ 107,816
Derivative liabilities - Fair Value	$ 256,528	$ 118,305
Customer Counterparty | Crude Oil
Derivative [Line Items]
Derivative, nonmonetary notional amount, energy measure | Boe	7,811	2,507
Customer Counterparty | Natural Gas
Derivative [Line Items]
Derivative, nonmonetary notional amount, energy measure | MMBTU	63,773	14,722
Derivative instruments not designated as hedging instruments
Derivative [Line Items]
Derivative assets - Fair value	$ 330,316	$ 107,816
Derivative liabilities - Fair Value	251,744	111,828
Derivative instruments not designated as hedging instruments | Commodity contracts
Derivative [Line Items]
Derivative assets - Fair value	81,380	14,422
Derivative liabilities - Fair Value	80,517	23,068
Commodity contracts | Derivative instruments not designated as hedging instruments | Customer Counterparty | Commodity contracts
Derivative [Line Items]
Derivative assets - Fair value	40,065	1,127
Derivative liabilities - Fair Value	$ 42,140	$ 22,687
Commodity contracts | Derivative instruments not designated as hedging instruments | Customer Counterparty | Crude Oil | Written options
Derivative [Line Items]
Derivative, nonmonetary notional amount, energy measure | Boe	36	524
Derivative assets - Fair value	$ 0	$ 0
Derivative liabilities - Fair Value	$ 30	$ 2,628
Commodity contracts | Derivative instruments not designated as hedging instruments | Customer Counterparty | Crude Oil | Collars
Derivative [Line Items]
Derivative, nonmonetary notional amount, energy measure | Boe	3,174	872
Derivative assets - Fair value	$ 2,673	$ 0
Derivative liabilities - Fair Value	$ 538	$ 3,772
Commodity contracts | Derivative instruments not designated as hedging instruments | Customer Counterparty | Crude Oil | Swaps
Derivative [Line Items]
Derivative, nonmonetary notional amount, energy measure | Boe	4,601	1,111
Derivative assets - Fair value	$ 6,949	$ 0
Derivative liabilities - Fair Value	$ 5,531	$ 14,278
Commodity contracts | Derivative instruments not designated as hedging instruments | Customer Counterparty | Crude Oil | Commodity contracts
Derivative [Line Items]
Derivative, nonmonetary notional amount, energy measure | Boe	7,811	2,507
Derivative assets - Fair value	$ 9,622	$ 0
Derivative liabilities - Fair Value	$ 6,099	$ 20,678
Commodity contracts | Derivative instruments not designated as hedging instruments | Customer Counterparty | Natural Gas | Written options
Derivative [Line Items]
Derivative, nonmonetary notional amount, energy measure | MMBTU	540
Derivative assets - Fair value	$ 0
Derivative liabilities - Fair Value	$ 22
Commodity contracts | Derivative instruments not designated as hedging instruments | Customer Counterparty | Natural Gas | Collars
Derivative [Line Items]
Derivative, nonmonetary notional amount, energy measure | MMBTU	14,277	3,063
Derivative assets - Fair value	$ 186	$ 78
Derivative liabilities - Fair Value	$ 522	$ 152
Commodity contracts | Derivative instruments not designated as hedging instruments | Customer Counterparty | Natural Gas | Swaps
Derivative [Line Items]
Derivative, nonmonetary notional amount, energy measure | MMBTU	48,956	11,659
Derivative assets - Fair value	$ 30,257	$ 1,049
Derivative liabilities - Fair Value	$ 35,497	$ 1,857
Commodity contracts | Derivative instruments not designated as hedging instruments | Customer Counterparty | Natural Gas | Commodity contracts
Derivative [Line Items]
Derivative, nonmonetary notional amount, energy measure | MMBTU	63,773	14,722
Derivative assets - Fair value	$ 30,443	$ 1,127
Derivative liabilities - Fair Value	36,041	2,009
Commodity contracts | Derivative instruments not designated as hedging instruments | Financial Counterparty | Commodity contracts
Derivative [Line Items]
Derivative assets - Fair value	41,315	13,295
Derivative liabilities - Fair Value	$ 38,377	$ 381
Commodity contracts | Derivative instruments not designated as hedging instruments | Financial Counterparty | Crude Oil | Purchased options
Derivative [Line Items]
Derivative, nonmonetary notional amount, energy measure | Boe	36	524
Derivative assets - Fair value	$ 29	$ 2,251
Derivative liabilities - Fair Value	$ 0	$ 0
Commodity contracts | Derivative instruments not designated as hedging instruments | Financial Counterparty | Crude Oil | Collars
Derivative [Line Items]
Derivative, nonmonetary notional amount, energy measure | Boe	3,630	872
Derivative assets - Fair value	$ 677	$ 3,225
Derivative liabilities - Fair Value	$ 2,815	$ 0
Commodity contracts | Derivative instruments not designated as hedging instruments | Financial Counterparty | Crude Oil | Swaps
Derivative [Line Items]
Derivative, nonmonetary notional amount, energy measure | Boe	4,721	1,111
Derivative assets - Fair value	$ 4,516	$ 5,799
Derivative liabilities - Fair Value	$ 5,215	$ 0
Commodity contracts | Derivative instruments not designated as hedging instruments | Financial Counterparty | Crude Oil | Commodity contracts
Derivative [Line Items]
Derivative, nonmonetary notional amount, energy measure | Boe	8,387	2,507
Derivative assets - Fair value	$ 5,222	$ 11,275
Derivative liabilities - Fair Value	$ 8,030	$ 0
Commodity contracts | Derivative instruments not designated as hedging instruments | Financial Counterparty | Natural Gas | Purchased options
Derivative [Line Items]
Derivative, nonmonetary notional amount, energy measure | MMBTU	530
Derivative assets - Fair value	$ 21
Derivative liabilities - Fair Value	$ 0
Commodity contracts | Derivative instruments not designated as hedging instruments | Financial Counterparty | Natural Gas | Collars
Derivative [Line Items]
Derivative, nonmonetary notional amount, energy measure | MMBTU	14,517	3,063
Derivative assets - Fair value	$ 471	$ 151
Derivative liabilities - Fair Value	$ 150	$ 64
Commodity contracts | Derivative instruments not designated as hedging instruments | Financial Counterparty | Natural Gas | Swaps
Derivative [Line Items]
Derivative, nonmonetary notional amount, energy measure | MMBTU	48,779	11,659
Derivative assets - Fair value	$ 35,601	$ 1,869
Derivative liabilities - Fair Value	$ 30,197	$ 317
Commodity contracts | Derivative instruments not designated as hedging instruments | Financial Counterparty | Natural Gas | Commodity contracts
Derivative [Line Items]
Derivative, nonmonetary notional amount, energy measure | MMBTU	63,826	14,722
Derivative assets - Fair value	$ 36,093	$ 2,020
Derivative liabilities - Fair Value	$ 30,347	$ 381