Marketable Investment Securities, Restricted Cash and Cash Equivalents, and Other Investment Securities - Investments Measured at Fair Value On A Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Fair value of marketable securities
Marketable Investment Securities	$ 40,202	$ 417,094
US Treasury and agency securities
Fair value of marketable securities
Marketable Investment Securities		10,016
Commercial paper
Fair value of marketable securities
Marketable Investment Securities	40,000	369,397
Corporate securities
Fair value of marketable securities
Marketable Investment Securities		28,796
Other
Fair value of marketable securities
Marketable Investment Securities	202	8,885
Fair value measurements on recurring basis
Fair value of marketable securities
Cash Equivalents (including restricted)	2,604,019	2,436,545
Total	40,202	417,094
Fair value measurements on recurring basis | US Treasury and agency securities
Fair value of marketable securities
Marketable Investment Securities		10,016
Fair value measurements on recurring basis | Commercial paper
Fair value of marketable securities
Marketable Investment Securities	40,000	369,397
Fair value measurements on recurring basis | Corporate securities
Fair value of marketable securities
Marketable Investment Securities		28,796
Fair value measurements on recurring basis | Other
Fair value of marketable securities
Marketable Investment Securities	202	8,885
Fair value measurements on recurring basis | Level 1
Fair value of marketable securities
Cash Equivalents (including restricted)	1,833,706	246,876
Total		10,016
Fair value measurements on recurring basis | Level 1 | US Treasury and agency securities
Fair value of marketable securities
Marketable Investment Securities		10,016
Fair value measurements on recurring basis | Level 2
Fair value of marketable securities
Cash Equivalents (including restricted)	770,313	2,189,669
Total	40,013	406,882
Fair value measurements on recurring basis | Level 2 | Commercial paper
Fair value of marketable securities
Marketable Investment Securities	40,000	369,397
Fair value measurements on recurring basis | Level 2 | Corporate securities
Fair value of marketable securities
Marketable Investment Securities		28,796
Fair value measurements on recurring basis | Level 2 | Other
Fair value of marketable securities
Marketable Investment Securities	13	8,689
Fair value measurements on recurring basis | Level 3
Fair value of marketable securities
Total	189	196
Fair value measurements on recurring basis | Level 3 | Other
Fair value of marketable securities
Marketable Investment Securities	$ 189	$ 196