Fair Value Measurements Fair Value Measurements (Level 3 Valuation Techniques) (Details) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis with Unobservable Inputs	$ 13,624	$ 0	$ (526)
Valuation, Income Approach
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis with Unobservable Inputs	$ 13,624
Valuation, Income Approach | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value Assumptions, Expected Volatility Rate for a Commodity	23.30%
Valuation, Income Approach | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value Assumptions, Expected Volatility Rate for a Commodity	43.50%