Goodwill and Other Intangible Assets, Net - Changes in Carrying Amount of Goodwill by Operating Segment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Finite-Lived Intangible Assets [Line Items]
Gross	$ 949,167	$ 903,904	$ 824,730
Accumulated impairment	(83,987)	(83,987)	(83,987)
Goodwill [Roll Forward]
Beginning balance, Goodwill	819,917	740,743
Additions	45,254	79,147
Divestitures and other adjustments	9	27
Ending balance, Goodwill	865,180	819,917
Financial Services
Finite-Lived Intangible Assets [Line Items]
Gross	591,237	549,906	470,732
Accumulated impairment	(44,047)	(44,047)	(44,047)
Goodwill [Roll Forward]
Beginning balance, Goodwill	505,859	426,685
Additions	41,322	79,147
Divestitures and other adjustments	9	27
Ending balance, Goodwill	547,190	505,859
Benefits and Insurance Services
Finite-Lived Intangible Assets [Line Items]
Gross	324,057	320,125	320,125
Accumulated impairment	(7,733)	(7,733)	(7,733)
Goodwill [Roll Forward]
Beginning balance, Goodwill	312,392	312,392
Additions	3,932	0
Divestitures and other adjustments	0	0
Ending balance, Goodwill	316,324	312,392
National Practices
Finite-Lived Intangible Assets [Line Items]
Gross	33,873	33,873	33,873
Accumulated impairment	(32,207)	(32,207)	$ (32,207)
Goodwill [Roll Forward]
Beginning balance, Goodwill	1,666	1,666
Additions	0	0
Divestitures and other adjustments	0	0
Ending balance, Goodwill	$ 1,666	$ 1,666