Fair Value Measurements Assets and Liabilities Measured on a Non-Recurring Basis (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Valuation adjustments to investments in joint venture arrangements	$ 0	$ 0	$ 0
Fair Value, Significant Unobservable Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Adjusted basis of inventory	14,515	3,823	12,921
Total losses	5,809	7,681	3,992
Initial basis of inventory	$ 20,324	$ 11,504	$ 16,913