Investments in Equity Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Debt and Equity Securities, FV-NI [Line Items]
Investments in equity securities	$ 2,122,818	$ 1,533,517
Charter
Debt and Equity Securities, FV-NI [Line Items]
Investments in equity securities	2,117,533	1,526,984
Other investments
Debt and Equity Securities, FV-NI [Line Items]
Investments in equity securities	$ 5,285	$ 6,533