MARKETABLE SECURITIES - Schedule of Underlying Maturities of AFS Securities (Details) $ in Thousands	Jun. 30, 2020 USD ($)
Available-for-sale securities
Due in one year or less, Cost	$ 678,771
Due in one year or less, Fair Value	679,587
Due after one year through four years, Cost	83,993
Due after one year through four years, Fair Value	84,666
Cash equivalents
Available-for-sale securities
Due in one year or less, Cost	246,905
Due in one year or less, Fair Value	246,907
Cash equivalents \| U.S. government agency securities
Available-for-sale securities
Due in one year or less, Cost	246,905
Due in one year or less, Fair Value	246,907
Marketable securities
Available-for-sale securities
Due in one year or less, Cost	431,866
Due in one year or less, Fair Value	432,680
Due after one year through four years, Cost	83,993
Due after one year through four years, Fair Value	84,666
Marketable securities \| U.S. government agency securities
Available-for-sale securities
Due in one year or less, Cost	249,239
Due in one year or less, Fair Value	249,295
Due after one year through four years, Cost	7,186
Due after one year through four years, Fair Value	7,231
Marketable securities \| Corporate bonds
Available-for-sale securities
Due in one year or less, Cost	162,241
Due in one year or less, Fair Value	162,992
Due after one year through four years, Cost	57,023
Due after one year through four years, Fair Value	57,569
Marketable securities \| Certificates of deposit
Available-for-sale securities
Due in one year or less, Cost	10,000
Due in one year or less, Fair Value	10,000
Due after one year through four years, Cost	0
Due after one year through four years, Fair Value	0
Marketable securities \| Commercial paper
Available-for-sale securities
Due in one year or less, Cost	7,996
Due in one year or less, Fair Value	8,000
Due after one year through four years, Cost	0
Due after one year through four years, Fair Value	0
Marketable securities \| Asset backed securities
Available-for-sale securities
Due in one year or less, Cost	2,390
Due in one year or less, Fair Value	2,393
Due after one year through four years, Cost	19,784
Due after one year through four years, Fair Value	$ 19,866

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