Business Combinations - Additional Information (Detail) shares in Millions	9 Months Ended
	Sep. 30, 2020 USD ($) Client_List shares	Sep. 30, 2019 USD ($) Business Client_List shares	Dec. 31, 2019 USD ($)
Business Acquisition, Contingent Consideration [Line Items]
Consideration paid in cash	$ 35,500,000	$ 19,400,000
Consideration paid in common stock	3,500,000	2,000,000.0
Contingent consideration	16,300,000	11,200,000
Contingent consideration arrangements - High	18,700,000	11,600,000
Aggregate fair value of contingent consideration	16,400,000	10,300,000
Contingent consideration, current	15,430,000		$ 16,193,000
Contingent consideration, non-current	18,678,000		$ 15,896,000
Annual revenue	24,600,000	$ 17,400,000
Number of businesses acquired | Business		6
Cash		$ 800,000
Acquired client funds		6,900,000
Business combination contingent consideration liability other adjustments based on projected future results of acquisition	(100,000)	300,000
Consideration paid in cash	$ 10,900,000	$ 16,300,000
Number of common stock issued | shares	0.1	0.1
Contingent Purchase Price Liability – Current [Member]
Business Acquisition, Contingent Consideration [Line Items]
Contingent consideration, current	$ 5,000,000.0	$ 2,900,000
Contingent Purchase Price Liability – Non-current [Member]
Business Acquisition, Contingent Consideration [Line Items]
Contingent consideration, non-current	$ 11,400,000	7,400,000
Alliance Insurance Services, Inc. [Member]
Business Acquisition, Contingent Consideration [Line Items]
Effective date of acquisition	Feb. 01, 2020
Acquired entity, name	Alliance Insurance Services, Inc.
Pension Dynamics Company, LLC [Member]
Business Acquisition, Contingent Consideration [Line Items]
Effective date of acquisition	Feb. 01, 2020
Acquired entity, name	Pension Dynamics Company, LLC
Sunshine Systems [Member]
Business Acquisition, Contingent Consideration [Line Items]
Effective date of acquisition	Feb. 01, 2020
Acquired entity, name	Sunshine Systems
Prince-Wood Insurance, L.L.C [Member]
Business Acquisition, Contingent Consideration [Line Items]
Effective date of acquisition	Jul. 01, 2020
Acquired entity, name	Prince-Wood Insurance, L.L.C
ARC Consulting LLC and ARC Placement Group LLC [Member]
Business Acquisition, Contingent Consideration [Line Items]
Effective date of acquisition	Sep. 01, 2020
Acquired entity, name	ARC Consulting LLC and ARC Placement Group LLC
Wenner Group, LLC [Member]
Business Acquisition, Contingent Consideration [Line Items]
Effective date of acquisition	Jan. 01, 2019
Acquired entity, name	Wenner Group, LLC
Paydayta, Inc. [Member]
Business Acquisition, Contingent Consideration [Line Items]
Effective date of acquisition	Jul. 01, 2019
Acquired entity, name	Paydayta, Inc.
Gavion, LLC [Member]
Business Acquisition, Contingent Consideration [Line Items]
Effective date of acquisition	Jul. 01, 2019
Acquired entity, name	Gavion, LLC
QBA Benefits, LLC. [Member]
Business Acquisition, Contingent Consideration [Line Items]
Effective date of acquisition	Aug. 01, 2019
Acquired entity, name	QBA Benefits, LLC.
Ericson CPAs [Member]
Business Acquisition, Contingent Consideration [Line Items]
Effective date of acquisition	Aug. 01, 2019
Acquired entity, name	Ericson CPAs
Brinig Taylor Zimmer, Inc. [Member]
Business Acquisition, Contingent Consideration [Line Items]
Effective date of acquisition	Sep. 01, 2019
Acquired entity, name	Brinig Taylor Zimmer, Inc.
Series of Business Acquisition [Member]
Business Acquisition, Contingent Consideration [Line Items]
Goodwill	$ 48,600,000	24,400,000
Acquisition of Client Lists [Member]
Business Acquisition, Contingent Consideration [Line Items]
Consideration paid in cash	600,000	300,000
Contingent consideration	$ 300,000	$ 200,000
Acquisition of Client Lists [Member] | Benefits and Insurance Services Practice Group [Member]
Business Acquisition, Contingent Consideration [Line Items]
Number of client list purchased | Client_List	2	1
Acquisition of Client Lists [Member] | Financial Service Practice Group [Member]
Business Acquisition, Contingent Consideration [Line Items]
Number of client list purchased | Client_List	1
Previous Client List Purchases [Member]
Business Acquisition, Contingent Consideration [Line Items]
Consideration paid in cash	$ 500,000	$ 700,000