FAIR VALUE MEASUREMENTS - RECURRING BASIS (Details) - Recurring basis - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Fair Value on a Recurring Basis
Total	$ 209,208	$ 254,454
Money market funds
Fair Value on a Recurring Basis
Total	24,207	4,356
U.S. Treasury securities
Fair Value on a Recurring Basis
Total	17,088	10,705
Municipal securities
Fair Value on a Recurring Basis
Total	2,985
Government-sponsored enterprise securities
Fair Value on a Recurring Basis
Total	12,493	28,757
Commercial paper
Fair Value on a Recurring Basis
Total	91,861	112,409
Corporate notes
Fair Value on a Recurring Basis
Total	60,574	97,866
Equity investment
Fair Value on a Recurring Basis
Total		361
Level 1
Fair Value on a Recurring Basis
Total	24,207	4,356
Level 1 | Money market funds
Fair Value on a Recurring Basis
Total	24,207	4,356
Level 2
Fair Value on a Recurring Basis
Total	185,001	250,098
Level 2 | U.S. Treasury securities
Fair Value on a Recurring Basis
Total	17,088	10,705
Level 2 | Municipal securities
Fair Value on a Recurring Basis
Total	2,985
Level 2 | Government-sponsored enterprise securities
Fair Value on a Recurring Basis
Total	12,493	28,757
Level 2 | Commercial paper
Fair Value on a Recurring Basis
Total	91,861	112,409
Level 2 | Corporate notes
Fair Value on a Recurring Basis
Total	$ 60,574	97,866
Level 2 | Equity investment
Fair Value on a Recurring Basis
Total		$ 361