SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Fair value measurements on recurring and nonrecurring valuation techniques (Details)	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Discount rate | Employment Agreement Award
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Assumptions Measurement Rate	9.50%	10.00%
Discount rate | Redeemable noncontrolling interests
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Assumptions Measurement Rate	12.50%	12.50%
Discount rate | Minimum | Employment Agreement Award
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Assumptions Measurement Rate	(2.10%)	(2.10%)
Discount rate | Maximum | Employment Agreement Award
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Assumptions Measurement Rate	2.50%	2.50%
Operating profit margin range | Minimum | Employment Agreement Award
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Assumptions Measurement Rate	33.90%	35.00%
Operating profit margin range | Minimum | Redeemable noncontrolling interests
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Assumptions Measurement Rate	24.50%	24.50%
Operating profit margin range | Maximum | Employment Agreement Award
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Assumptions Measurement Rate	41.20%	42.30%
Operating profit margin range | Maximum | Redeemable noncontrolling interests
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Assumptions Measurement Rate	31.90%	31.90%
Revenue growth rate range | Minimum | Redeemable noncontrolling interests
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Assumptions Measurement Rate	1.20%	1.20%
Revenue growth rate range | Maximum | Redeemable noncontrolling interests
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Assumptions Measurement Rate	16.50%	16.50%
Average recurring EBITDA multiple | Minimum | Employment Agreement Award
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Assumptions Measurement Rate	6.00%	6.30%
Average recurring EBITDA multiple | Maximum | Employment Agreement Award
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Assumptions Measurement Rate	6.10%	6.50%
Exit MultipleExit Multiple | Redeemable noncontrolling interests
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Assumptions Measurement Rate	4.00%	4.00%