Derivative Financial Instruments Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2017		Dec. 31, 2016
Fair value of derivative assets and liabilities
Derivative, Fair Value, Net	$ (31,700)		$ (91,700)
Derivative asset current	63,685		54,521
Derivative asset noncurrent	60,035		67,575
Derivative Asset, Fair Value, Gross Asset	123,720		122,096
Derivative liability current	87,791		115,464
Derivatives liability noncurrent	67,676		98,340
Derivative Liability, Fair Value, Gross Liability	155,467		213,804
Derivatives not designated as hedging instruments
Fair value of derivative assets and liabilities
Derivative asset current	63,685		54,521
Derivative asset noncurrent	60,035		67,575
Derivative liability current	87,791		115,464
Derivatives liability noncurrent	67,676		98,340
Fair Value, Inputs, Level 2 [Member] | Derivatives not designated as hedging instruments | Fair Value, Measurements, Recurring [Member]
Fair value of derivative assets and liabilities
Derivative Asset, Fair Value, Gross Asset	123,720	[1]	122,096	[2]
Derivative Liability, Fair Value, Gross Liability	$ 155,467	[1]	$ 213,804	[2]

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

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