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Organization and Summary of Significant Accounting Policies - Change in Accounting Estimate (Details) - Transportation
12 Months Ended
Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]  
Useful life 10 years
Scenario, Previously Reported  
New Accounting Pronouncements or Change in Accounting Principle [Line Items]  
Useful life 20 years