FAIR VALUE OF FINANCIAL INSTRUMENTS - Fair Value Measurements of Contingent Consideration (Details) - Level 3 - Fair Value, Recurring - Discounted cash flow, Monte Carlo |
9 Months Ended | 12 Months Ended |
|---|---|---|
Sep. 30, 2021 |
Dec. 31, 2020 |
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis | ||
| Expected years | 2 years 7 months 6 days | 3 years 6 months |
| Present value discount rate | ||
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis | ||
| Contingent consideration, measurement input | 25.50% | 25.80% |
| Volatility factor | ||
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis | ||
| Contingent consideration, measurement input | 51.00% | 51.80% |