Derivative Financial Instruments Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2019		Dec. 31, 2018
Fair value of derivative assets and liabilities
Derivative, fair value, net	$ 61,700		$ 158,300
Derivative assets, current	114,242		175,130
Derivative assets, noncurrent	30,180		58,499
Total derivative assets	144,422		233,629
Derivative liabilities, current	70,259		62,853
Derivatives liabilities, noncurrent	12,431		12,496
Total derivative liabilities	82,690		75,349
Derivative asset, amounts not offset in the accompanying balance sheets	(60,210)		(56,041)
Derivative liabilities, amounts not offset in the accompanying balance sheets	60,210		56,041
Derivative asset, fair value, net amounts	84,212		177,588
Derivative liabilities, fair value, net amounts	(22,480)		(19,308)
Not Designated as Hedging Instrument [Member]
Fair value of derivative assets and liabilities
Derivative assets, current	114,242		175,130
Derivative assets, noncurrent	30,180		58,499
Derivative liabilities, current	70,259		62,853
Derivatives liabilities, noncurrent	12,431		12,496
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	144,422	[1]	233,629	[2]
Total derivative liabilities	$ 82,690	[1]	$ 75,349	[2]

[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.