Commitments and Contingencies (Legal Proceedings) - Additional Information (Detail) $ in Millions			9 Months Ended
	Dec. 19, 2016 USD ($)	Sep. 16, 2016 USD ($)	Sep. 30, 2020 USD ($) Plaintiff
Baldino Group [Member]
Commitments And Contingencies [Line Items]
Number of Plaintiffs | Plaintiff			2
Damages sought amount			$ 16.0
Altoona Regional Health System [Member]
Commitments And Contingencies [Line Items]
Loss contingency, expected trial commencement		2021-03
Altoona Regional Health System [Member] | Minimum [Member]
Commitments And Contingencies [Line Items]
Damages sought amount		$ 124.0
Altoona Regional Health System [Member] | Maximum [Member]
Commitments And Contingencies [Line Items]
Damages sought amount		$ 266.0
CBIZ Operations and a former employee of CBIZ MMP [Member]
Commitments And Contingencies [Line Items]
Loss contingency, expected trial commencement	2021-03
Total transaction price	$ 200.0
CBIZ Operations and a former employee of CBIZ MMP [Member] | Maximum [Member]
Commitments And Contingencies [Line Items]
Damages sought amount	$ 177.0