Derivative Financial Instruments Fair Value (Details) $ in Thousands	Dec. 31, 2018 USD ($)		Dec. 31, 2017 USD ($)		Dec. 31, 2016
Fair value of derivative assets and liabilities
Derivative, Fair Value, Net	$ 158,300		$ (139,400)
Derivative Assets, Current	175,130		64,266
Derivative Assets, Noncurrent	58,499		40,362
Total Derivative Assets	233,629		104,628
Derivative Liabilities, Current	62,853		172,582
Derivative Liabilities, Noncurrent	12,496		71,402
Total Derivative Liabilities	(75,349)		(243,984)
Derivative Asset, Not Offset in the Accompanying Balance Sheets	(56,041)		(100,035)
Derivative Liabilities, Not Offset in the Accompanying Balance Sheets	56,041		100,035
Derivative Asset, Fair Value, Net Amounts	177,588		4,593
Derivative Liability, Fair Value, Net Amounts	19,308		143,949
Not Designated as Hedging Instrument [Member]
Fair value of derivative assets and liabilities
Derivative Assets, Current	175,130		64,266
Derivative Assets, Noncurrent	58,499		40,362
Derivative Liabilities, Current	62,853		172,582
Derivative Liabilities, Noncurrent	12,496		71,402
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Not Designated as Hedging Instrument [Member]
Fair value of derivative assets and liabilities
Total Derivative Assets	233,629	[1]	104,628	[2]
Total Derivative Liabilities	$ (75,349)	[1]	$ (243,984)	[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.