Fair Value Measurements (Narrative) (Details) - Weighted Average [Member] - Fair Value, Measurements, Recurring [Member] - Significant Unobservable Inputs (Level 3) [Member]	Mar. 31, 2018	Dec. 31, 2017
Inventory Related Payables [Member]
Fair Value Measurements [Line Items]
Basis	177.80%	99.90%
Inventories Carried At Market [Member]
Fair Value Measurements [Line Items]
Basis	20.30%	12.80%