SEGMENT DISCLOSURES - Schedule of Segment Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Segment Reporting Information [Line Items]
Revenue	$ 1,813,472	$ 1,591,194	$ 1,411,979
Corporate & other:
General & administrative expenses	108,753	57,965	55,023
Interest expense	34,379	20,131	8,039
Other income (expense), net	(13,538)	(21,019)	19,243
Income before income tax expense	57,807	166,303	141,475
Financial Services
Segment Reporting Information [Line Items]
Revenue	1,362,539	1,160,686	1,010,068
Benefits and Insurance Services
Segment Reporting Information [Line Items]
Revenue	401,048	382,605	358,007
National Practices
Segment Reporting Information [Line Items]
Revenue	49,885	47,903	43,904
Operating Segments
Segment Reporting Information [Line Items]
Revenue	1,813,472	1,591,194	1,411,979
Personnel costs	1,272,809	1,077,080	951,258
Facility costs	67,836	56,890	55,698
Other costs, gains, and losses, net	240,173	190,399	169,592
Total segment expense	1,580,818	1,324,369	1,176,548
Corporate & other:
Income before income tax expense	232,654	266,825	235,431
Operating Segments | Financial Services
Segment Reporting Information [Line Items]
Revenue	1,362,539	1,160,686	1,010,068
Personnel costs	972,730	793,791	688,555
Facility costs	55,178	44,444	42,617
Other costs, gains, and losses, net	185,091	134,623	118,184
Total segment expense	1,212,999	972,858	849,356
Corporate & other:
Income before income tax expense	149,540	187,828	160,712
Operating Segments | Benefits and Insurance Services
Segment Reporting Information [Line Items]
Revenue	401,048	382,605	358,007
Personnel costs	257,166	242,340	225,871
Facility costs	12,481	12,196	12,831
Other costs, gains, and losses, net	58,476	53,916	49,299
Total segment expense	328,123	308,452	288,001
Corporate & other:
Income before income tax expense	72,925	74,153	70,006
Operating Segments | National Practices
Segment Reporting Information [Line Items]
Revenue	49,885	47,903	43,904
Personnel costs	42,913	40,949	36,832
Facility costs	177	250	250
Other costs, gains, and losses, net	(3,394)	1,860	2,109
Total segment expense	39,696	43,059	39,191
Corporate & other:
Income before income tax expense	10,189	4,844	4,713
Corporate And Eliminations
Corporate & other:
Unallocated corporate operating expenses	44,485	39,344	8,986
General & administrative expenses	108,753	57,965	55,023
Interest expense	34,374	20,129	8,033
Other income (expense), net	$ (12,765)	$ (16,916)	$ 21,914