Marketable Investment Securities, Restricted Cash and Cash Equivalents, and Other Investment Securities - Unrealized Gain (Losses) On Marketable Investment Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Components of our available-for-sale investments
Marketable Investment Securities	$ 417,094	$ 1,246,120
Unrealized Gains (Losses) on Marketable Investment Securities
Unrealized Gains	96	187
Unrealized Losses	(1)	(920)
Unrealized Gains Losses, Net	95	(733)
Accumulated net unrealized losses
Accumulated net unrealized gain (loss), before tax, in accumulated other comprehensive income (loss)	1,000	(1,000)
Accumulated net unrealized gain (loss), net of tax, in accumulated other comprehensive income (loss)	1,000	(1,000)
Contractual maturities of restricted and non-restricted marketable investment securities
Debt securities with contractual maturities within one year	417,000
US Treasury and agency securities
Components of our available-for-sale investments
Marketable Investment Securities	10,016	66,823
Unrealized Gains (Losses) on Marketable Investment Securities
Unrealized Gains	32	40
Unrealized Losses		(19)
Unrealized Gains Losses, Net	32	21
Commercial paper
Components of our available-for-sale investments
Marketable Investment Securities	369,397	367,488
Unrealized Gains (Losses) on Marketable Investment Securities
Unrealized Gains	2
Unrealized Gains Losses, Net	2
Corporate securities
Components of our available-for-sale investments
Marketable Investment Securities	28,796	805,259
Unrealized Gains (Losses) on Marketable Investment Securities
Unrealized Gains	4	91
Unrealized Losses	(1)	(899)
Unrealized Gains Losses, Net	3	(808)
Other
Components of our available-for-sale investments
Marketable Investment Securities	8,885	6,550
Unrealized Gains (Losses) on Marketable Investment Securities
Unrealized Gains	58	56
Unrealized Losses		(2)
Unrealized Gains Losses, Net	$ 58	$ 54