Annual report pursuant to Section 13 and 15(d)

Investments in Charter Accounted for Using the Equity Method (Details)

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Investments in Charter Accounted for Using the Equity Method (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2016
Dec. 31, 2017
Investments in affiliates accounted for using the Equity Method      
Cash paid to acquire equity method investments   $ 5,000,000  
Charter      
Investments in affiliates accounted for using the Equity Method      
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity $ 3,298,000   $ 2,975,000
A/N | Charter      
Investments in affiliates accounted for using the Equity Method      
Proxy agreement term 5 years    
Trading days before proposed sale of A/N 2 days    
first | A/N | Charter      
Investments in affiliates accounted for using the Equity Method      
Business Acquisition, Percentage of Voting Interests Acquired 25.01%    
Maximum percentage of New Charter shares that may be voted by proxy 7.00%    
last | A/N | Charter      
Investments in affiliates accounted for using the Equity Method      
Maximum percentage of New Charter shares that may be voted by proxy 7.00%