Derivative Financial Instruments Fair Value (Details) $ in Thousands	Dec. 31, 2019 USD ($)		Dec. 31, 2018 USD ($)		Dec. 31, 2017
Fair value of derivative assets and liabilities
Derivative, Fair Value, Net	$ 21,500		$ 158,300
Derivative Assets, Current	55,184		175,130
Derivative Assets, Noncurrent	20,624		58,499
Total Derivative Assets	75,808		233,629
Derivative Liabilities, Current	50,846		62,853
Derivative Liabilities, Noncurrent	3,444		12,496
Total Derivative Liabilities	(54,290)		(75,349)
Derivative Asset, Not Offset in the Accompanying Balance Sheets	(35,075)		(56,041)
Derivative Liabilities, Not Offset in the Accompanying Balance Sheets	35,075		56,041
Derivative Asset, Fair Value, Net Amounts	40,733		177,588
Derivative Liability, Fair Value, Net Amounts	(19,215)		(19,308)
Not Designated as Hedging Instrument [Member]
Fair value of derivative assets and liabilities
Derivative Assets, Current	55,184		175,130
Derivative Assets, Noncurrent	20,624		58,499
Derivative Liabilities, Current	50,846		62,853
Derivative Liabilities, Noncurrent	3,444		12,496
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Not Designated as Hedging Instrument [Member]
Fair value of derivative assets and liabilities
Total Derivative Assets	75,808	[1]	233,629	[2]
Total Derivative Liabilities	$ 54,290	[1]	$ 75,349	[2]
Designated as Hedging Instrument [Member]
Fair value of derivative assets and liabilities
Derivative, Number of Instruments Held	0		0		0

[1] ⁽¹⁾  This represents a financial asset or liability that is measured at fair value on a recurring basis.

[2] ⁽¹⁾  This represents a financial asset or liability that is measured at fair value on a recurring basis.