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Investments in Unconsolidated Entities - Additional Information (Detail) - USD ($)
 3 Months Ended 9 Months Ended 12 Months Ended
Mar. 31, 2017
Sep. 30, 2018
Dec. 31, 2012
Schedule of Equity Method Investments [Line Items]      
Investment carrying value   $ 529,882  
Chatham Rock Phosphate, Ltd. [Member]      
Schedule of Equity Method Investments [Line Items]      
Investment carrying value     $ 0
Deep sea mining exploratory services     $ 1,680,000
Shares received from CRP 142,100   9,320,348
Outstanding equity stake in CRP 1.00%    
Neptune Minerals, Inc. [Member]      
Schedule of Equity Method Investments [Line Items]      
Ownership percentage   14.00%  
Investment carrying value   $ 0  
Neptune Minerals, Inc. [Member] | Common Class A [Member]      
Schedule of Equity Method Investments [Line Items]      
Shares owned   0  
Neptune Minerals, Inc. [Member] | Common Class B Non Voting Shares [Member]      
Schedule of Equity Method Investments [Line Items]      
Current investment position in NMI   3,092,488  
Aggregate number of shares converted   261,200  
Neptune Minerals, Inc. [Member] | Series A Preferred Non Voting Shares [Member]      
Schedule of Equity Method Investments [Line Items]      
Current investment position in NMI   2,612  
Dorado Ocean Resources, Ltd. [Member]      
Schedule of Equity Method Investments [Line Items]      
Loss from unconsolidated entity   $ 21,300,000