Segment Disclosures - Summary of Disaggregation of Revenue by Source (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disaggregation of Revenue [Line Items]
Total revenue	$ 300,730	$ 277,455
Financial Services
Disaggregation of Revenue [Line Items]
Total revenue	204,149	188,777
Benefits & Insurance
Disaggregation of Revenue [Line Items]
Total revenue	87,239	79,612
National Practices
Disaggregation of Revenue [Line Items]
Total revenue	9,342	9,066
Accounting, tax, advisory and consulting
Disaggregation of Revenue [Line Items]
Total revenue	204,149	188,777
Accounting, tax, advisory and consulting | Financial Services
Disaggregation of Revenue [Line Items]
Total revenue	204,149	188,777
Accounting, tax, advisory and consulting | Benefits & Insurance
Disaggregation of Revenue [Line Items]
Total revenue	0	0
Accounting, tax, advisory and consulting | National Practices
Disaggregation of Revenue [Line Items]
Total revenue	0	0
Core benefits and insurance services
Disaggregation of Revenue [Line Items]
Total revenue	84,070	76,472
Core benefits and insurance services | Financial Services
Disaggregation of Revenue [Line Items]
Total revenue	0	0
Core benefits and insurance services | Benefits & Insurance
Disaggregation of Revenue [Line Items]
Total revenue	84,070	76,472
Core benefits and insurance services | National Practices
Disaggregation of Revenue [Line Items]
Total revenue	0	0
Non-core benefits and insurance services
Disaggregation of Revenue [Line Items]
Total revenue	3,169	3,140
Non-core benefits and insurance services | Financial Services
Disaggregation of Revenue [Line Items]
Total revenue	0	0
Non-core benefits and insurance services | Benefits & Insurance
Disaggregation of Revenue [Line Items]
Total revenue	3,169	3,140
Non-core benefits and insurance services | National Practices
Disaggregation of Revenue [Line Items]
Total revenue	0	0
Managed networking, hardware services
Disaggregation of Revenue [Line Items]
Total revenue	6,895	6,575
Managed networking, hardware services | Financial Services
Disaggregation of Revenue [Line Items]
Total revenue	0	0
Managed networking, hardware services | Benefits & Insurance
Disaggregation of Revenue [Line Items]
Total revenue	0	0
Managed networking, hardware services | National Practices
Disaggregation of Revenue [Line Items]
Total revenue	6,895	6,575
National practices consulting
Disaggregation of Revenue [Line Items]
Total revenue	2,447	2,491
National practices consulting | Financial Services
Disaggregation of Revenue [Line Items]
Total revenue	0	0
National practices consulting | Benefits & Insurance
Disaggregation of Revenue [Line Items]
Total revenue	0	0
National practices consulting | National Practices
Disaggregation of Revenue [Line Items]
Total revenue	$ 2,447	$ 2,491