Goodwill and Other Intangible Assets, Net - Changes in Carrying Amount of Goodwill by Operating Segment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Finite-Lived Intangible Assets [Line Items]
Gross	$ 903,904	$ 824,730	$ 767,070
Accumulated impairment	(83,987)	(83,987)	(83,987)
Goodwill [Roll Forward]
Beginning balance, Goodwill	740,743	683,083
Additions	79,147	60,446
Divestitures		(2,786)
Other adjustment	27
Ending balance, Goodwill	819,917	740,743
Financial Services
Finite-Lived Intangible Assets [Line Items]
Gross	549,906	470,732	412,086
Accumulated impairment	(44,047)	(44,047)	(44,047)
Goodwill [Roll Forward]
Beginning balance, Goodwill	426,685	368,039
Additions	79,147	58,646
Divestitures		0
Other adjustment	27
Ending balance, Goodwill	505,859	426,685
Benefits and Insurance Services
Finite-Lived Intangible Assets [Line Items]
Gross	320,125	320,125	321,111
Accumulated impairment	(7,733)	(7,733)	(7,733)
Goodwill [Roll Forward]
Beginning balance, Goodwill	312,392	313,378
Additions	0	1,800
Divestitures		(2,786)
Other adjustment	0
Ending balance, Goodwill	312,392	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		0
Other adjustment	0
Ending balance, Goodwill	$ 1,666	$ 1,666