FAIR VALUE MEASUREMENTS - SECURITY TYPE (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Included in cash and cash equivalents:
Amortized Cost	$ 31,706
Estimated Fair Value	31,706
Restricted cash:
Amortized Cost	364	$ 363
Estimated Fair Value	364	363
Marketable securities:
Amortized Cost	177,675	249,659
Gross Unrealized Gains	4	111
Gross Unrealized Losses	(177)	(33)
Estimated Fair Value	177,502	249,737
Money market funds
Included in cash and cash equivalents:
Amortized Cost	24,207	4,356
Estimated Fair Value	24,207	4,356
Restricted cash:
Amortized Cost	93	92
Estimated Fair Value	93	92
Commercial paper
Included in cash and cash equivalents:
Amortized Cost	7,499
Estimated Fair Value	7,499
Certificate of deposit
Restricted cash:
Amortized Cost	271	271
Estimated Fair Value	271	271
U.S. Treasury securities (due in less than one year)
Marketable securities:
Amortized Cost	15,585	5,608
Gross Unrealized Gains		2
Gross Unrealized Losses	(18)
Estimated Fair Value	15,567	5,610
U.S. Treasury securities (due in one to two years)
Marketable securities:
Amortized Cost	1,524	5,093
Gross Unrealized Gains		2
Gross Unrealized Losses	(3)
Estimated Fair Value	1,521	5,095
Municipal securities (due in one to two years)
Marketable securities:
Amortized Cost	3,000
Gross Unrealized Losses	(15)
Estimated Fair Value	2,985
Government-sponsored enterprise securities (due in less than one year)
Marketable securities:
Amortized Cost	12,500	5,249
Gross Unrealized Gains		3
Gross Unrealized Losses	(7)
Estimated Fair Value	12,493	5,252
Government-sponsored enterprise securities (due in one to two years)
Marketable securities:
Amortized Cost		23,499
Gross Unrealized Gains		7
Gross Unrealized Losses		(1)
Estimated Fair Value		23,505
Commercial paper (due in less than one year)
Marketable securities:
Amortized Cost	84,398	112,388
Gross Unrealized Gains	2	29
Gross Unrealized Losses	(38)	(8)
Estimated Fair Value	84,362	112,409
Corporate notes (due in less than one year)
Marketable securities:
Amortized Cost	36,444	63,051
Gross Unrealized Gains	2	35
Gross Unrealized Losses	(17)	(7)
Estimated Fair Value	36,429	63,079
Corporate notes (due in one to two years)
Marketable securities:
Amortized Cost	24,224	34,771
Gross Unrealized Gains		33
Gross Unrealized Losses	(79)	(17)
Estimated Fair Value	$ 24,145	$ 34,787

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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