Goodwill and Other Intangible Assets, Net - Changes in Carrying Amount of Goodwill by Operating Segment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Gross	$ 824,730	$ 767,070	$ 672,200
Accumulated impairment	(83,987)	(83,987)	(83,987)
Goodwill [Roll Forward]
Beginning balance, Goodwill	683,083	588,213
Additions	60,446	97,439
Divestitures and other adjustment	(2,786)	(2,569)
Ending balance, Goodwill	740,743	683,083
Financial Services
Finite-Lived Intangible Assets [Line Items]
Gross	470,732	412,086	378,294
Accumulated impairment	(44,047)	(44,047)	(44,047)
Goodwill [Roll Forward]
Beginning balance, Goodwill	368,039	334,247
Additions	58,646	34,785
Divestitures and other adjustment	0	(993)
Ending balance, Goodwill	426,685	368,039
Benefits and Insurance Services
Finite-Lived Intangible Assets [Line Items]
Gross	320,125	321,111	260,033
Accumulated impairment	(7,733)	(7,733)	(7,733)
Goodwill [Roll Forward]
Beginning balance, Goodwill	313,378	252,300
Additions	1,800	62,654
Divestitures and other adjustment	(2,786)	(1,576)
Ending balance, Goodwill	312,392	313,378
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 adjustment	0	0
Ending balance, Goodwill	$ 1,666	$ 1,666