Acquisitions (Details Textual) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012 ClientList Business	Dec. 31, 2011 ClientList Business	Dec. 31, 2010 Business
Acquisitions (Textual) [Abstract]
Consideration paid in cash	$ 79,300,000				$ 11,800,000				$ 79,300,000	$ 11,800,000	$ 29,400,000
Fair value of contingent consideration	17,600,000				13,400,000				17,600,000	13,400,000	13,100,000
Consideration paid in common stock	4,200,000				3,300,000				4,200,000	3,300,000	3,500,000
Other income, net	3,254,000	2,570,000	(840,000)	3,438,000	4,851,000	(4,510,000)	27,000	3,081,000	8,422,000	3,449,000	3,532,000
CBIZ contingent consideration	17,600,000				13,400,000				17,600,000	13,400,000	16,300,000
Contingent arrangements arising from acquisitions in the current year	20,900,000								20,900,000
Goodwill	62,900,000				16,900,000				62,900,000	16,900,000	34,000,000
Goodwill	440,709,000				377,281,000				440,709,000	377,281,000	344,086,000
Acquisitions (Additional Textual) [Abstract]
Number of common stock issued									402,000	38,900	13,100
Short-term notes payable	5,300,000								5,300,000
Guaranteed future consideration	1,700,000				1,100,000				1,700,000	1,100,000	400,000
Goodwill at the time of acquisition	62,900,000				16,900,000				62,900,000	16,900,000	34,000,000
Number of client list purchased									1	1
Reduction of contingent purchase price liability fair value									1,100,000	3,500,000	1,400,000
Interest expense									2,100,000
Amortization expense									2,800,000
Number of Businesses Acquired									9	4	4
Maximum [Member]
Acquisitions (Textual) [Abstract]
Contingent arrangements arising from acquisitions in the current year					15,100,000					15,100,000	17,000,000
Minimum [Member]
Acquisitions (Textual) [Abstract]
Contingent arrangements arising from acquisitions in the current year					0					0	0
Meridian Insurance Group, LLC (Meridian), Primarily Care, Inc. (PCI) Stoltz and Company, LTD., L.L.P (Stoltz), Trinity Risk Advisors, Inc.(Trinity), Strategic Employee Benefit Services-The Pruett Group, Inc. (SEBS-Pruett), ProMedical, Inc. (ProMedical), the employee benefit division of Leavitt Pacific Insurance Brokers, Inc. (Leavitt), Diversified Industries, Inc. d/b/a Payroll Control Systems (PCS) and PHBV Partners, L.L.P. (PHBV) [Member]
Acquisitions (Textual) [Abstract]
Goodwill	62,931,000								62,931,000
Business acquisition, Revenue recorded									26,600,000
Acquisitions (Additional Textual) [Abstract]
Goodwill at the time of acquisition	62,931,000								62,931,000
Thompson Dunavant PLC, Multiple Benefit Services, Inc. (MBS), Gresham Smith LLC and Atlantic MDR, LLC (d/b/a Advantage Benefit Planning) (ABP) [Member]
Acquisitions (Textual) [Abstract]
Goodwill					16,869,000					16,869,000
Acquisitions (Additional Textual) [Abstract]
Goodwill at the time of acquisition					16,869,000					16,869,000
Goldstein Lewin & Company, National Benefit Alliance, South Winds, Inc. (d/b/a Benexx) and Kirkland, Russ, Murphy & Tapp [Member]
Acquisitions (Textual) [Abstract]
Fair value of contingent consideration											3,300,000
Goodwill											33,986,000
Acquisitions (Additional Textual) [Abstract]
Goodwill at the time of acquisition											33,986,000
Thompson Dunavant PLC and Multiple Benefit Services Inc [Member]
Acquisitions (Textual) [Abstract]
Consideration paid in cash											29,400,000
Aggregate Consideration of Acquisitions					29,600,000					29,600,000	49,600,000
Consideration paid in common stock					3,300,000					3,300,000	3,500,000
Amount Paid by Company									25,600,000	16,700,000	20,000,000
CBIZ adjusted the fair value of the contingent purchase price liability related to CBIZs prior acquisitions									1,100,000	3,500,000
CBIZ contingent consideration											16,300,000
Common stock issuable									41,314	251,100	265,000
Goodwill	58,100,000				11,800,000				58,100,000	11,800,000
Acquisitions (Additional Textual) [Abstract]
Goodwill at the time of acquisition	58,100,000				11,800,000				58,100,000	11,800,000
Thompson Dunavant PLC and Multiple Benefit Services Inc [Member] | Maximum [Member]
Acquisitions (Textual) [Abstract]
Fair value of contingent consideration											5,600,000
Thompson Dunavant PLC and Multiple Benefit Services Inc [Member] | Minimum [Member]
Acquisitions (Textual) [Abstract]
CBIZ adjusted the fair value of the contingent purchase price liability related to CBIZs prior acquisitions											4,200,000
Other non-current liabilities [Member]
Acquisitions (Textual) [Abstract]
Fair value of contingent consideration	11,900,000				9,300,000				11,900,000	9,300,000	10,500,000
Other current liabilities [Member]
Acquisitions (Textual) [Abstract]
Fair value of contingent consideration	5,700,000				4,100,000				5,700,000	4,100,000	2,600,000
Client lists [Member]
Acquisitions (Textual) [Abstract]
Consideration paid in cash at closing										800,000
Contingent liability for purchase of client lists	$ 2,500,000				$ 600,000				$ 2,500,000	$ 600,000