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Related Party Transactions - Guarantees - Additional Information (Detail) - Archer [Member] - Equity Method Investee [Member] - USD ($)
6 Months Ended
Feb. 05, 2015
Jun. 30, 2018
Jun. 30, 2017
Dec. 31, 2017
Property Lease Guarantee [Member]        
Related Party Transaction [Line Items]        
Guarantee period 10 years      
Guarantee outstanding   $ 9,000,000    
Maximum potential future payment       $ 10,000,000
Guarantee Fees Reimbursed [Member]        
Related Party Transaction [Line Items]        
Revenues related party   $ 0 $ 0