Fair Value Measurements Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2018		Dec. 31, 2017
Assets
Derivatives	$ 90,016		$ 104,628
Liabilities
Derivatives	376,764		243,984
Not Designated as Hedging Instrument [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets
Derivatives	0	[1]	0	[2]
Liabilities
Derivatives	0	[1]	0	[2]
Not Designated as Hedging Instrument [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets
Derivatives	90,016	[1]	104,628	[2]
Liabilities
Derivatives	376,764	[1]	243,984	[2]
Not Designated as Hedging Instrument [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Assets
Derivatives	0	[1]	0	[2]
Liabilities
Derivatives	$ 0	[1]	$ 0	[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.