Revenue - Summary of Disaggregation of Revenue by Source (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Total revenue	$ 1,104,925	$ 963,897	$ 948,424
Financial Services
Disaggregation of Revenue [Line Items]
Total revenue	734,026	629,778	616,567
Benefits and Insurance Services
Disaggregation of Revenue [Line Items]
Total revenue	332,323	297,758	296,228
National Practices
Disaggregation of Revenue [Line Items]
Total revenue	38,576	36,361	35,629
Accounting, tax, advisory and consulting
Disaggregation of Revenue [Line Items]
Total revenue	734,026	629,778	616,567
Accounting, tax, advisory and consulting | Financial Services
Disaggregation of Revenue [Line Items]
Total revenue	734,026	629,778	616,567
Core Benefits and Insurance Services
Disaggregation of Revenue [Line Items]
Total revenue	319,684	286,361	283,783
Core Benefits and Insurance Services | Benefits and Insurance Services
Disaggregation of Revenue [Line Items]
Total revenue	319,684	286,361	283,783
Non-core Benefits and Insurance Services
Disaggregation of Revenue [Line Items]
Total revenue	12,639	11,397	12,445
Non-core Benefits and Insurance Services | Benefits and Insurance Services
Disaggregation of Revenue [Line Items]
Total revenue	12,639	11,397	12,445
Managed networking, hardware services
Disaggregation of Revenue [Line Items]
Total revenue	28,456	26,458	25,982
Managed networking, hardware services | National Practices
Disaggregation of Revenue [Line Items]
Total revenue	28,456	26,458	25,982
National Practices consulting
Disaggregation of Revenue [Line Items]
Total revenue	10,120	9,903	9,647
National Practices consulting | National Practices
Disaggregation of Revenue [Line Items]
Total revenue	$ 10,120	$ 9,903	$ 9,647