Financial Instruments - Investments in Debt and Marketable Equity Securities Disclosure (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Cost or Amortized Cost
Cash and cash equivalents, at carrying value	$ 371,573	$ 234,679
Cash, Cash Equivalents, Restricted Cash
Cash, cash equivalents, restricted cash and restricted cash equivalents	387,966	247,448	$ 219,218	$ 439,055
Fair Value, Measurements, Recurring
Cost or Amortized Cost
Restricted cash	16,393	12,769
Cash, cash equivalents, and available-for-sale debt securities, amortized cost	534,555	348,446
Unrealized Gains (Losses)
Unrealized Gains	292	31
Unrealized Losses	0	(22)
Estimated Fair Value
Cash and cash equivalents, fair value disclosure	342,172
Cash, cash equivalents, and available-for-sale debt securities	534,847	348,455
Cash, Cash Equivalents, Restricted Cash
Cash, cash equivalents, restricted cash and restricted cash equivalents	387,966	247,448
Short-term Investments
Short-term investments	129,809	70,029
Long-term Investments
Long-term investments	17,072	30,978
U.S. treasury securities | Fair Value, Measurements, Recurring
Cost or Amortized Cost
Debt securities, available-for-sale, amortized cost	140,040	100,998
Unrealized Gains (Losses)
Unrealized Gains	270	31
Unrealized Losses	0	(22)
Estimated Fair Value
Debt securities, available-for-sale	140,310	101,007
Short-term Investments
Short-term investments	129,809	70,029
Long-term Investments
Long-term investments	5,150	30,978
Agency bonds | Fair Value, Measurements, Recurring
Cost or Amortized Cost
Debt securities, available-for-sale, amortized cost	11,900
Unrealized Gains (Losses)
Unrealized Gains	22
Unrealized Losses	0
Estimated Fair Value
Debt securities, available-for-sale	11,922
Short-term Investments
Short-term investments	0
Long-term Investments
Long-term investments	11,922
Cash | Fair Value, Measurements, Recurring
Cost or Amortized Cost
Cash and cash equivalents, at carrying value	29,401	13,237
Estimated Fair Value
Cash and cash equivalents, fair value disclosure	29,401	13,237
Cash, Cash Equivalents, Restricted Cash
Cash, cash equivalents, restricted cash and restricted cash equivalents	29,401	13,237
Money markets funds | Fair Value, Measurements, Recurring
Cost or Amortized Cost
Cash and cash equivalents, at carrying value	336,821	221,442
Estimated Fair Value
Cash and cash equivalents, fair value disclosure	336,821	221,442
Cash, Cash Equivalents, Restricted Cash
Cash, cash equivalents, restricted cash and restricted cash equivalents	336,821	$ 221,442
U.S. treasury securities | Fair Value, Measurements, Recurring
Cash, Cash Equivalents, Restricted Cash
Cash, cash equivalents, restricted cash and restricted cash equivalents	$ 5,351