FINANCIAL INSTRUMENTS - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Cash equivalents:
Cash equivalents		$ 197,615
Short-term investments:
Short-term investments	$ 12,453	0
Total assets	14,506
Time deposits
Short-term investments:
Short-term investments	12,453
Quoted Market Prices in Active Markets for Identical Assets (Level 1)
Cash equivalents:
Cash equivalents		147,615
Short-term investments:
Total assets	2,053
Quoted Market Prices in Active Markets for Identical Assets (Level 1) | Time deposits
Short-term investments:
Short-term investments	0
Significant Other Observable Inputs (Level 2)
Cash equivalents:
Cash equivalents		50,000
Short-term investments:
Total assets	12,453
Significant Other Observable Inputs (Level 2) | Time deposits
Short-term investments:
Short-term investments	12,453
Money market funds
Cash equivalents:
Cash equivalents	2,053	147,615
Money market funds | Quoted Market Prices in Active Markets for Identical Assets (Level 1)
Cash equivalents:
Cash equivalents	2,053	147,615
Money market funds | Significant Other Observable Inputs (Level 2)
Cash equivalents:
Cash equivalents	$ 0	0
Time deposits
Cash equivalents:
Cash equivalents		50,000
Time deposits | Quoted Market Prices in Active Markets for Identical Assets (Level 1)
Cash equivalents:
Cash equivalents		0
Time deposits | Significant Other Observable Inputs (Level 2)
Cash equivalents:
Cash equivalents		$ 50,000