Segment Disclosures - Summary of Disaggregation of Revenue by Source (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Total revenue	$ 278,648	$ 236,943	$ 579,378	$ 514,398
Financial Services
Disaggregation of Revenue [Line Items]
Total revenue	186,589	154,083	390,738	342,860
Benefits & Insurance
Disaggregation of Revenue [Line Items]
Total revenue	82,620	73,940	169,859	153,552
National Practices
Disaggregation of Revenue [Line Items]
Total revenue	9,439	8,920	18,781	17,986
Accounting, tax, advisory and consulting
Disaggregation of Revenue [Line Items]
Total revenue	186,589	154,083	390,738	342,860
Accounting, tax, advisory and consulting | Financial Services
Disaggregation of Revenue [Line Items]
Total revenue	186,589	154,083	390,738	342,860
Accounting, tax, advisory and consulting | Benefits & Insurance
Disaggregation of Revenue [Line Items]
Total revenue	0	0	0	0
Accounting, tax, advisory and consulting | National Practices
Disaggregation of Revenue [Line Items]
Total revenue	0	0	0	0
Core benefits and insurance services
Disaggregation of Revenue [Line Items]
Total revenue	79,288	71,393	163,358	147,865
Core benefits and insurance services | Financial Services
Disaggregation of Revenue [Line Items]
Total revenue	0	0	0	0
Core benefits and insurance services | Benefits & Insurance
Disaggregation of Revenue [Line Items]
Total revenue	79,288	71,393	163,358	147,865
Core benefits and insurance services | National Practices
Disaggregation of Revenue [Line Items]
Total revenue	0	0	0	0
Non-core benefits and insurance services
Disaggregation of Revenue [Line Items]
Total revenue	3,332	2,547	6,501	5,687
Non-core benefits and insurance services | Financial Services
Disaggregation of Revenue [Line Items]
Total revenue	0	0	0	0
Non-core benefits and insurance services | Benefits & Insurance
Disaggregation of Revenue [Line Items]
Total revenue	3,332	2,547	6,501	5,687
Non-core benefits and insurance services | National Practices
Disaggregation of Revenue [Line Items]
Total revenue	0	0	0	0
Managed networking, hardware services
Disaggregation of Revenue [Line Items]
Total revenue	6,969	6,581	13,864	13,156
Managed networking, hardware services | Financial Services
Disaggregation of Revenue [Line Items]
Total revenue	0	0	0	0
Managed networking, hardware services | Benefits & Insurance
Disaggregation of Revenue [Line Items]
Total revenue	0	0	0	0
Managed networking, hardware services | National Practices
Disaggregation of Revenue [Line Items]
Total revenue	6,969	6,581	13,864	13,156
National practices consulting
Disaggregation of Revenue [Line Items]
Total revenue	2,470	2,339	4,917	4,830
National practices consulting | Financial Services
Disaggregation of Revenue [Line Items]
Total revenue	0	0	0	0
National practices consulting | Benefits & Insurance
Disaggregation of Revenue [Line Items]
Total revenue	0	0	0	0
National practices consulting | National Practices
Disaggregation of Revenue [Line Items]
Total revenue	$ 2,470	$ 2,339	$ 4,917	$ 4,830