Fair Value Measurements Fair Value Measurements (Level 3 Valuation Techniques) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016
Fair Value Measurements, Recurring and nonrecurring, Valuation Techniques [Line Items]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis with Unobservable Inputs	$ (6,412)	$ (1,168)	$ 0	$ 2	$ 99	$ (526)
Income Approach Valuation Technique
Fair Value Measurements, Recurring and nonrecurring, Valuation Techniques [Line Items]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis with Unobservable Inputs	$ (6,412)
Income Approach Valuation Technique | Minimum
Fair Value Measurements, Recurring and nonrecurring, Valuation Techniques [Line Items]
Expected Volatility Range	20.70%
Income Approach Valuation Technique | Maximum
Fair Value Measurements, Recurring and nonrecurring, Valuation Techniques [Line Items]
Expected Volatility Range	29.90%