CASH AND INVESTMENTS - Schedule of Cash, Cash Equivalents, and Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Cash		$ 67,818
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Fair Value	$ 0	122,648
Agency bonds
Debt Securities, Available-for-sale [Line Items]
Fair Value	0	3,968
Certificates of deposit
Debt Securities, Available-for-sale [Line Items]
Fair Value	0	3,937
US treasury securities
Debt Securities, Available-for-sale [Line Items]
Fair Value	0	70,089
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Fair Value	0	27,551
Cash equivalents:
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		148,089
Unrealized Gains		1
Unrealized Losses		(1)
Fair Value		148,089
Cash equivalents: \| Money market funds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		126,075
Unrealized Gains		0
Unrealized Losses		0
Fair Value		126,075
Cash equivalents: \| Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		1,000
Unrealized Gains		0
Unrealized Losses		0
Fair Value		1,000
Cash equivalents: \| Agency bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		6,485
Unrealized Gains		1
Unrealized Losses		0
Fair Value		6,486
Cash equivalents: \| Commercial paper
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		9,609
Unrealized Gains		0
Unrealized Losses		(1)
Fair Value		9,608
Cash equivalents: \| Certificates of deposit
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		171
Unrealized Gains		0
Unrealized Losses		0
Fair Value		171
Cash equivalents: \| US treasury securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		4,749
Unrealized Gains		0
Unrealized Losses		0
Fair Value		4,749
Total cash and cash equivalents
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		215,907
Unrealized Gains		1
Unrealized Losses		(1)
Fair Value		215,907
Short-term investments:
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		201,399
Unrealized Gains		189
Unrealized Losses		(9)
Fair Value		201,579
Short-term investments: \| Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		103,130
Unrealized Gains		110
Unrealized Losses		(7)
Fair Value		103,233
Short-term investments: \| Agency bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		3,966
Unrealized Gains		2
Unrealized Losses		0
Fair Value		3,968
Short-term investments: \| Commercial paper
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		23,827
Unrealized Gains		1
Unrealized Losses		0
Fair Value		23,828
Short-term investments: \| Certificates of deposit
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		3,936
Unrealized Gains		2
Unrealized Losses		(1)
Fair Value		3,937
Short-term investments: \| US treasury securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		50,703
Unrealized Gains		62
Unrealized Losses		(1)
Fair Value		50,764
Short-term investments: \| Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		15,837
Unrealized Gains		12
Unrealized Losses		0
Fair Value		15,849
Total long-term marketable investments
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		50,400
Unrealized Gains		47
Unrealized Losses		(5)
Fair Value	$ 0	50,442
Total long-term marketable investments \| Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		19,407
Unrealized Gains		12
Unrealized Losses		(4)
Fair Value		19,415
Total long-term marketable investments \| US treasury securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		19,300
Unrealized Gains		25
Unrealized Losses		0
Fair Value		19,325
Total long-term marketable investments \| Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		11,693
Unrealized Gains		10
Unrealized Losses		(1)
Fair Value		$ 11,702

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on 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, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on 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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