FAIR VALUE MEASUREMENTS - Schedule of Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Fair value measurements
Cash and cash equivalents, and restricted cash	$ 704,208	$ 177,528
Marketable securities	764,253	175,007
Equity securities	1,385	1,716
Restricted cash
Fair value measurements
Cash and cash equivalents, and restricted cash	282	274
Fair Value, Recurring
Fair value measurements
Equity securities	1,385	1,716
Contingent consideration	(2,551)	(2,879)
Total	1,220,388	321,050
Fair Value, Recurring \| Corporate bonds
Fair value measurements
Marketable securities	220,561	4,003
Fair Value, Recurring \| U.S. government agency securities
Fair value measurements
Marketable securities	256,526	140,682
Fair Value, Recurring \| Certificates of deposit
Fair value measurements
Marketable securities	10,000
Fair Value, Recurring \| Asset backed securities
Fair value measurements
Marketable securities	22,259
Fair Value, Recurring \| Commercial paper
Fair value measurements
Marketable securities	8,000
Fair Value, Recurring \| Cash and money market
Fair value measurements
Cash and cash equivalents, and restricted cash	457,019	146,932
Fair Value, Recurring \| U.S. government agency securities
Fair value measurements
Cash and cash equivalents, and restricted cash	246,907	30,322
Fair Value, Recurring \| Restricted cash
Fair value measurements
Cash and cash equivalents, and restricted cash	282	274
Level 1 \| Fair Value, Recurring
Fair value measurements
Equity securities	1,385	1,716
Contingent consideration	0	0
Total	458,686	148,922
Level 1 \| Fair Value, Recurring \| Corporate bonds
Fair value measurements
Marketable securities	0	0
Level 1 \| Fair Value, Recurring \| U.S. government agency securities
Fair value measurements
Marketable securities	0	0
Level 1 \| Fair Value, Recurring \| Certificates of deposit
Fair value measurements
Marketable securities	0
Level 1 \| Fair Value, Recurring \| Asset backed securities
Fair value measurements
Marketable securities	0
Level 1 \| Fair Value, Recurring \| Commercial paper
Fair value measurements
Marketable securities	0
Level 1 \| Fair Value, Recurring \| Cash and money market
Fair value measurements
Cash and cash equivalents, and restricted cash	457,019	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	282	274
Level 2 \| Fair Value, Recurring
Fair value measurements
Equity securities	0	0
Contingent consideration	0	0
Total	764,253	175,007
Level 2 \| Fair Value, Recurring \| Corporate bonds
Fair value measurements
Marketable securities	220,561	4,003
Level 2 \| Fair Value, Recurring \| U.S. government agency securities
Fair value measurements
Marketable securities	256,526	140,682
Level 2 \| Fair Value, Recurring \| Certificates of deposit
Fair value measurements
Marketable securities	10,000
Level 2 \| Fair Value, Recurring \| Asset backed securities
Fair value measurements
Marketable securities	22,259
Level 2 \| Fair Value, Recurring \| Commercial paper
Fair value measurements
Marketable securities	8,000
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	246,907	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	(2,551)	(2,879)
Total	(2,551)	(2,879)
Level 3 \| Fair Value, Recurring \| Corporate bonds
Fair value measurements
Marketable securities	0	0
Level 3 \| Fair Value, Recurring \| U.S. government agency securities
Fair value measurements
Marketable securities	0	0
Level 3 \| Fair Value, Recurring \| Certificates of deposit
Fair value measurements
Marketable securities	0
Level 3 \| Fair Value, Recurring \| Asset backed securities
Fair value measurements
Marketable securities	0
Level 3 \| Fair Value, Recurring \| Commercial paper
Fair value measurements
Marketable securities	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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