Derivatives (Derivatives Not Designated as Hedging Instruments - Commodity Contracts) (Details) MMBTU in Thousands, Boe in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) MMBTU Boe	Dec. 31, 2019 USD ($) MMBTU Boe
Derivative [Line Items]
Derivative assets - Fair value	$ 602,754	$ 330,316
Derivative liabilities - Fair Value	$ 424,828	$ 256,528
Customer Counterparty | Crude Oil
Derivative [Line Items]
Derivative, nonmonetary notional amount, energy measure | Boe	6,321	7,811
Customer Counterparty | Natural Gas
Derivative [Line Items]
Derivative, nonmonetary notional amount, energy measure | MMBTU	109,635	63,773
Derivative instruments not designated as hedging instruments
Derivative [Line Items]
Derivative assets - Fair value	$ 602,754	$ 330,316
Derivative liabilities - Fair Value	422,729	251,744
Derivative instruments not designated as hedging instruments | Commodity contracts
Derivative [Line Items]
Derivative assets - Fair value	82,451	81,380
Derivative liabilities - Fair Value	84,165	80,517
Commodity contracts | Derivative instruments not designated as hedging instruments | Customer Counterparty | Commodity contracts
Derivative [Line Items]
Derivative assets - Fair value	44,762	40,065
Derivative liabilities - Fair Value	$ 43,978	$ 42,140
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
Derivative assets - Fair value		$ 0
Derivative liabilities - Fair Value		$ 30
Commodity contracts | Derivative instruments not designated as hedging instruments | Customer Counterparty | Crude Oil | Collars
Derivative [Line Items]
Derivative, nonmonetary notional amount, energy measure | Boe	2,022	3,174
Derivative assets - Fair value	$ 2,344	$ 2,673
Derivative liabilities - Fair Value	$ 2,193	$ 538
Commodity contracts | Derivative instruments not designated as hedging instruments | Customer Counterparty | Crude Oil | Swaps
Derivative [Line Items]
Derivative, nonmonetary notional amount, energy measure | Boe	4,299	4,601
Derivative assets - Fair value	$ 9,282	$ 6,949
Derivative liabilities - Fair Value	$ 14,283	$ 5,531
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	6,321	7,811
Derivative assets - Fair value	$ 11,626	$ 9,622
Derivative liabilities - Fair Value	$ 16,476	$ 6,099
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	597	540
Derivative assets - Fair value	$ 0	$ 0
Derivative liabilities - Fair Value	$ 59	$ 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	12,733	14,277
Derivative assets - Fair value	$ 1,063	$ 186
Derivative liabilities - Fair Value	$ 205	$ 522
Commodity contracts | Derivative instruments not designated as hedging instruments | Customer Counterparty | Natural Gas | Swaps
Derivative [Line Items]
Derivative, nonmonetary notional amount, energy measure | MMBTU	96,305	48,956
Derivative assets - Fair value	$ 32,073	$ 30,257
Derivative liabilities - Fair Value	$ 27,238	$ 35,497
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	109,635	63,773
Derivative assets - Fair value	$ 33,136	$ 30,443
Derivative liabilities - Fair Value	27,502	36,041
Commodity contracts | Derivative instruments not designated as hedging instruments | Financial Counterparty | Commodity contracts
Derivative [Line Items]
Derivative assets - Fair value	37,689	41,315
Derivative liabilities - Fair Value	$ 40,187	$ 38,377
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
Derivative assets - Fair value		$ 29
Derivative liabilities - Fair Value		$ 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	2,022	3,630
Derivative assets - Fair value	$ 2,217	$ 677
Derivative liabilities - Fair Value	$ 2,402	$ 2,815
Commodity contracts | Derivative instruments not designated as hedging instruments | Financial Counterparty | Crude Oil | Swaps
Derivative [Line Items]
Derivative, nonmonetary notional amount, energy measure | Boe	4,299	4,721
Derivative assets - Fair value	$ 8,220	$ 4,516
Derivative liabilities - Fair Value	$ 7,135	$ 5,215
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	6,321	8,387
Derivative assets - Fair value	$ 10,437	$ 5,222
Derivative liabilities - Fair Value	$ 9,537	$ 8,030
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	597	530
Derivative assets - Fair value	$ 59	$ 21
Derivative liabilities - Fair Value	$ 0	$ 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	16,293	14,517
Derivative assets - Fair value	$ 205	$ 471
Derivative liabilities - Fair Value	$ 813	$ 150
Commodity contracts | Derivative instruments not designated as hedging instruments | Financial Counterparty | Natural Gas | Swaps
Derivative [Line Items]
Derivative, nonmonetary notional amount, energy measure | MMBTU	103,973	48,779
Derivative assets - Fair value	$ 26,988	$ 35,601
Derivative liabilities - Fair Value	$ 29,837	$ 30,197
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	120,863	63,826
Derivative assets - Fair value	$ 27,252	$ 36,093
Derivative liabilities - Fair Value	$ 30,650	$ 30,347