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Other Current Liability - Summary of Revenue Recognized in Relation to Contract Liabilities (Detail)
$ in Thousands
12 Months Ended
Dec. 31, 2018
USD ($)
Current contract liabilities  
Revenue recognized that was included in the contract liabilities balance at the beginning of the year $ 113
Transportation Service  
Current contract liabilities  
Revenue recognized that was included in the contract liabilities balance at the beginning of the year 28
Custodial service  
Current contract liabilities  
Revenue recognized that was included in the contract liabilities balance at the beginning of the year $ 85