FAIR VALUE MEASUREMENT - Nonmonetary transaction (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Exchange for accounts receivable	$ 1.6
Prepaid Expenses and Other Current Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
common stock and related securities prepaid expenses	3.4
Other Nonoperating Income (Expense)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized gains/losses	$ 1.8