Marketable Investment Securities - Schedule of Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Schedule of Investments [Line Items]
Total debt securities	$ 913,150	$ 2,200,650
Equity securities	35,566	90,976
Total marketable investment securities	948,716	2,291,626
Less: Restricted marketable investment securities	8,093	9,474
Marketable investment securities	940,623	2,282,152
Corporate bonds
Schedule of Investments [Line Items]
Total debt securities	577,570	1,735,653
Other debt securities
Schedule of Investments [Line Items]
Total debt securities	$ 335,580	$ 464,997