Quarterly report pursuant to Section 13 or 15(d)

Assets and Liabilities Measured at Fair Value (Schedule of Assets and Liabilities) (Details)

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Assets and Liabilities Measured at Fair Value (Schedule of Assets and Liabilities) (Details) - USD ($)
$ in Thousands
Sep. 30, 2018
Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Cash equivalents $ 638,999 $ 570,526
Equity securities 1,749,132 1,800,208
Investment in Liberty Broadband 3,598,079 3,634,786
Indemnification obligation 99,858 0
Exchangeable senior debentures 527,000 0
Exchangeable senior debentures    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Exchangeable senior debentures 527,361 0
Variable forward    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Variable forward 26,980 94,807
Quoted prices in active markets for identical assets (Level 1)    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Cash equivalents 638,999 570,526
Equity securities 1,749,132 1,800,208
Investment in Liberty Broadband 3,598,079 3,634,786
Indemnification obligation 0 0
Quoted prices in active markets for identical assets (Level 1) | Exchangeable senior debentures    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Exchangeable senior debentures 0 0
Quoted prices in active markets for identical assets (Level 1) | Variable forward    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Variable forward 0 0
Significant other observable inputs (Level 2)    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Cash equivalents 0 0
Equity securities 0 0
Investment in Liberty Broadband 0 0
Indemnification obligation 99,858 0
Significant other observable inputs (Level 2) | Exchangeable senior debentures    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Exchangeable senior debentures 527,361 0
Significant other observable inputs (Level 2) | Variable forward    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Variable forward $ 26,980 $ 94,807