Quarterly report pursuant to Section 13 or 15(d)

Equity Method Investments Schedule of Summarized Financial Information (Details)

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Equity Method Investments Schedule of Summarized Financial Information (Details) - USD ($)
3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Dec. 31, 2017
Equity Method Investments and Joint Ventures [Abstract]          
Current assets $ 37,257   $ 37,257   $ 35,859
Non-current assets 23,247   23,247   21,009
Current liabilities 16,626   16,626   15,151
Non-current liabilities 2,930   2,930   1,056
Revenue 29,068,000 $ 32,986,000 64,905,000 $ 67,419,000  
Net income 4,200,000 $ 4,527,000 10,098,000 $ 10,975,000  
Schedule of Equity Method Investments [Line Items]          
Carrying value 135,430,000   135,430,000   137,299,000
Wireless Maritime Services          
Schedule of Equity Method Investments [Line Items]          
Carrying value $ 135,430,000   $ 135,430,000   $ 137,299