Derivative Financial Instruments Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2019		Dec. 31, 2018
Fair value of derivative assets and liabilities
Derivative, fair value, net	$ (13,800)		$ 158,300
Derivative assets, current	67,567		175,130
Derivative assets, noncurrent	27,202		58,499
Total derivative assets	94,769		233,629
Derivative liabilities, current	95,269		62,853
Derivatives liabilities, noncurrent	13,332		12,496
Total derivative liabilities	108,601		75,349
Derivative asset, not offset in the accompanying balance sheets	(52,882)		(56,041)
Derivative liabilities, not offset in the accompanying balance sheets	52,882		56,041
Derivative asset, fair value, net amounts	41,887		177,588
Derivative liabilities, fair value, net amounts	(55,719)		(19,308)
Not Designated as Hedging Instrument [Member]
Fair value of derivative assets and liabilities
Derivative assets, current	67,567		175,130
Derivative assets, noncurrent	27,202		58,499
Derivative liabilities, current	95,269		62,853
Derivatives liabilities, noncurrent	13,332		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	94,769	[1]	233,629	[2]
Total derivative liabilities	$ 108,601	[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.