Marketable Investment Securities, Restricted Cash and Cash Equivalents, and Other Investment Securities - Unrealized Gain (Losses) On Marketable Investment Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Components of our available-for-sale investments
Debt securities	$ 561,113	$ 417,094
Unrealized Gains (Losses) on Marketable Investment Securities
Unrealized Gains	22	96
Unrealized Losses	(135)	(1)
Unrealized Gains Losses, Net	(113)	95
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	561,000
US Treasury and agency securities
Components of our available-for-sale investments
Debt securities	5,011	10,016
Unrealized Gains (Losses) on Marketable Investment Securities
Unrealized Gains	22	32
Unrealized Gains Losses, Net	22	32
Commercial paper
Components of our available-for-sale investments
Debt securities	484,969	369,397
Unrealized Gains (Losses) on Marketable Investment Securities
Unrealized Gains		2
Unrealized Gains Losses, Net		2
Corporate securities
Components of our available-for-sale investments
Debt securities	69,194	28,796
Unrealized Gains (Losses) on Marketable Investment Securities
Unrealized Gains		4
Unrealized Losses	(135)	(1)
Unrealized Gains Losses, Net	(135)	3
Other
Components of our available-for-sale investments
Debt securities	$ 1,939	8,885
Unrealized Gains (Losses) on Marketable Investment Securities
Unrealized Gains		58
Unrealized Gains Losses, Net		$ 58