Investments in Equity Securities (Tables)  | 
3 Months Ended | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Mar. 31, 2018  | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Investments, Debt and Equity Securities [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Investments in Equity Securities | 
 Investments in equity securities, the majority of which are carried at fair value, are summarized as follows: 
 (a) A portion of the Charter equity securities are considered covered shares and subject to certain contractual restrictions in accordance with the indemnification agreement. See note 6 for additional discussion of the indemnification agreement. 
(b) The Company has elected the measurement alternative for these securities. 
 | 
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| X | ||||||||||
- References No definition available. 
  | 
| X | ||||||||||
- Definition Tabular disclosure of investments in trading securities. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
  |