FAIR VALUE MEASUREMENTS - Schedule of Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Fair value measurements
Cash and cash equivalents, and restricted cash	$ 806,969	$ 177,528
Estimated Fair Value	824,883	175,007
Equity securities	1,418	1,716
Restricted cash
Fair value measurements
Cash and cash equivalents, and restricted cash	291	274
Fair Value, Recurring
Fair value measurements
Equity securities	1,418	1,716
Contingent consideration	(2,638)	(2,879)
Total	1,280,655	321,050
Fair Value, Recurring \| Corporate bonds
Fair value measurements
Estimated Fair Value	192,621	4,003
Fair Value, Recurring \| U.S. government agency securities
Fair value measurements
Estimated Fair Value	257,162	140,682
Fair Value, Recurring \| Certificates of deposit
Fair value measurements
Estimated Fair Value	10,001
Fair Value, Recurring \| Asset backed securities
Fair value measurements
Estimated Fair Value	15,122
Fair Value, Recurring \| Cash and money market
Fair value measurements
Cash and cash equivalents, and restricted cash	456,701	146,932
Fair Value, Recurring \| U.S. government agency securities
Fair value measurements
Cash and cash equivalents, and restricted cash	349,977	30,322
Fair Value, Recurring \| Restricted cash
Fair value measurements
Cash and cash equivalents, and restricted cash	291	274
Level 1 \| Fair Value, Recurring
Fair value measurements
Equity securities	1,418	1,716
Contingent consideration	0	0
Total	458,410	148,922
Level 1 \| Fair Value, Recurring \| Corporate bonds
Fair value measurements
Estimated Fair Value	0	0
Level 1 \| Fair Value, Recurring \| U.S. government agency securities
Fair value measurements
Estimated Fair Value	0	0
Level 1 \| Fair Value, Recurring \| Certificates of deposit
Fair value measurements
Estimated Fair Value	0
Level 1 \| Fair Value, Recurring \| Asset backed securities
Fair value measurements
Estimated Fair Value	0
Level 1 \| Fair Value, Recurring \| Cash and money market
Fair value measurements
Cash and cash equivalents, and restricted cash	456,701	146,932
Level 1 \| Fair Value, Recurring \| U.S. government agency securities
Fair value measurements
Cash and cash equivalents, and restricted cash	0	0
Level 1 \| Fair Value, Recurring \| Restricted cash
Fair value measurements
Cash and cash equivalents, and restricted cash	291	274
Level 2 \| Fair Value, Recurring
Fair value measurements
Equity securities	0	0
Contingent consideration	0	0
Total	824,883	175,007
Level 2 \| Fair Value, Recurring \| Corporate bonds
Fair value measurements
Estimated Fair Value	192,621	4,003
Level 2 \| Fair Value, Recurring \| U.S. government agency securities
Fair value measurements
Estimated Fair Value	257,162	140,682
Level 2 \| Fair Value, Recurring \| Certificates of deposit
Fair value measurements
Estimated Fair Value	10,001
Level 2 \| Fair Value, Recurring \| Asset backed securities
Fair value measurements
Estimated Fair Value	15,122
Level 2 \| Fair Value, Recurring \| Cash and money market
Fair value measurements
Cash and cash equivalents, and restricted cash	0	0
Level 2 \| Fair Value, Recurring \| U.S. government agency securities
Fair value measurements
Cash and cash equivalents, and restricted cash	349,977	30,322
Level 2 \| Fair Value, Recurring \| Restricted cash
Fair value measurements
Cash and cash equivalents, and restricted cash	0	0
Level 3 \| Fair Value, Recurring
Fair value measurements
Equity securities	0	0
Contingent consideration	(2,638)	(2,879)
Total	(2,638)	(2,879)
Level 3 \| Fair Value, Recurring \| Corporate bonds
Fair value measurements
Estimated Fair Value	0	0
Level 3 \| Fair Value, Recurring \| U.S. government agency securities
Fair value measurements
Estimated Fair Value	0	0
Level 3 \| Fair Value, Recurring \| Certificates of deposit
Fair value measurements
Estimated Fair Value	0
Level 3 \| Fair Value, Recurring \| Asset backed securities
Fair value measurements
Estimated Fair Value	0
Level 3 \| Fair Value, Recurring \| Cash and money market
Fair value measurements
Cash and cash equivalents, and restricted cash	0	0
Level 3 \| Fair Value, Recurring \| U.S. government agency securities
Fair value measurements
Cash and cash equivalents, and restricted cash	0	0
Level 3 \| Fair Value, Recurring \| Restricted cash
Fair value measurements
Cash and cash equivalents, and restricted cash	$ 0	$ 0

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of liability recognized arising from contingent consideration in a business combination, expected to be settled within one year or the normal operating cycle, if longer.

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Fair value of asset after deduction of liability.

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