Derivative Financial Instruments Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2018		Dec. 31, 2017
Fair value of derivative assets and liabilities
Derivative, fair value, net	$ (286,700)		$ (139,400)
Derivative assets, current	81,163		64,266
Derivative assets, noncurrent	8,853		40,362
Total derivative assets	90,016		104,628
Derivative liabilities, current	304,159		172,582
Derivatives liabilities, noncurrent	72,605		71,402
Total derivative liabilities	376,764		243,984
Derivative asset, not offset in the accompanying balance sheets	(90,016)		(100,035)
Derivative liabilities, not offset in the accompanying balance sheets	90,016		100,035
Derivative asset, fair value, net amounts	0		4,593
Derivative liabilities, fair value, net amounts	(286,748)		(143,949)
Not Designated as Hedging Instrument [Member]
Fair value of derivative assets and liabilities
Derivative assets, current	81,163		64,266
Derivative assets, noncurrent	8,853		40,362
Derivative liabilities, current	304,159		172,582
Derivatives liabilities, noncurrent	72,605		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	90,016	[1]	104,628	[2]
Total derivative liabilities	$ 376,764	[1]	$ 243,984	[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.