Marketable Investment Securities, Restricted Cash and Cash Equivalents, and Other Investment Securities - Unrealized Gains (Losses) On Marketable Investment Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Accumulated net unrealized gains (losses)
Accumulated net unrealized gains, net of tax, in accumulated other comprehensive income (loss)		$ 0
Unrealized Gains (Losses) on Marketable Investment Securities
Unrealized Gains	$ 4
Unrealized Losses	(15)	$ 0
Unrealized Gains Losses, Net	(11)
Contractual maturities of restricted and non-restricted marketable investment securities
Debt securities with contractual maturities within one year	61,000
Maximum
Accumulated net unrealized gains (losses)
Accumulated net unrealized gains, net of tax, in accumulated other comprehensive income (loss)	1,000
Unrealized Gains (Losses) on Marketable Investment Securities
Unrealized Losses	(1,000)
U.S. Treasury and agency securities
Unrealized Gains (Losses) on Marketable Investment Securities
Unrealized Gains	4
Unrealized Gains Losses, Net	4
Corporate securities
Unrealized Gains (Losses) on Marketable Investment Securities
Unrealized Losses	(15)
Unrealized Gains Losses, Net	$ (15)