Marketable Securities and Fair Value Measurements - Schedule of Financial Assets Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair value measurements
Cash equivalents	$ 582,753	$ 849,461
Total	1,147,771	975,265
Short-term Investments
Fair value measurements
Short term investments	404,252	114,278
Certificate of deposit
Fair value measurements
Other non-current assets	5,076	5,000
Investment securities
Fair value measurements
Long term investments	155,690	6,526
Cash
Fair value measurements
Cash equivalents	308,521	134,375
Cash equivalents
Fair value measurements
Cash equivalents	274,232	715,086
Level 1
Fair value measurements
Cash equivalents	582,753	849,461
Total	587,829	854,461
Level 1 | Short-term Investments
Fair value measurements
Short term investments	0	0
Level 1 | Certificate of deposit
Fair value measurements
Other non-current assets	5,076	5,000
Level 1 | Investment securities
Fair value measurements
Long term investments	0	0
Level 1 | Cash
Fair value measurements
Cash equivalents	308,521	134,375
Level 1 | Cash equivalents
Fair value measurements
Cash equivalents	274,232	715,086
Level 2
Fair value measurements
Cash equivalents	0	0
Total	559,942	120,804
Level 2 | Short-term Investments
Fair value measurements
Short term investments	404,252	114,278
Level 2 | Certificate of deposit
Fair value measurements
Other non-current assets	0	0
Level 2 | Investment securities
Fair value measurements
Long term investments	155,690	6,526
Level 2 | Cash
Fair value measurements
Cash equivalents	0	0
Level 2 | Cash equivalents
Fair value measurements
Cash equivalents	0	0
Level 3
Fair value measurements
Cash equivalents	0	0
Total	0	0
Level 3 | Short-term Investments
Fair value measurements
Short term investments	0	0
Level 3 | Certificate of deposit
Fair value measurements
Other non-current assets	0	0
Level 3 | Investment securities
Fair value measurements
Long term investments	0	0
Level 3 | Cash
Fair value measurements
Cash equivalents	0	0
Level 3 | Cash equivalents
Fair value measurements
Cash equivalents	$ 0	$ 0