Segment Disclosures - Summary of Disaggregation of Revenue by Source (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation Of Revenue [Line Items]
Total revenue	$ 238,389	$ 239,790	$ 752,787	$ 745,286
Financial Services [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	155,499	153,794	498,359	493,311
Benefits and Insurance Services [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	73,881	76,960	227,433	225,342
National Practices [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	9,009	9,036	26,995	26,633
Accounting, Tax, Advisory and Consulting [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	155,499	153,794	498,359	493,311
Accounting, Tax, Advisory and Consulting [Member] | Financial Services [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	155,499	153,794	498,359	493,311
Core Benefits and Insurance Services [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	71,497	73,409	219,362	216,394
Core Benefits and Insurance Services [Member] | Benefits and Insurance Services [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	71,497	73,409	219,362	216,394
Non-core Benefits and Insurance Services [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	2,384	3,551	8,071	8,948
Non-core Benefits and Insurance Services [Member] | Benefits and Insurance Services [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	2,384	3,551	8,071	8,948
Managed Networking, Hardware Services [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	6,592	6,553	19,748	19,499
Managed Networking, Hardware Services [Member] | National Practices [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	6,592	6,553	19,748	19,499
National Practices Consulting [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	2,417	2,483	7,247	7,134
National Practices Consulting [Member] | National Practices [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	$ 2,417	$ 2,483	$ 7,247	$ 7,134