Commitments, Contingencies and Off-Balance Sheet Arrangements - Additional Information (Detail) (USD $)	12 Months Ended			144 Months Ended
	Dec. 31, 2013 LetterOfCredit Entity sqft	Dec. 31, 2012 Entity	Dec. 31, 2011 Entity	Dec. 31, 2013 Entity
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Acquired property through lease area, sqft.	306,000
Acquired property through lease percentage of building	60.00%
Operating lease commitment, expiration date	Feb. 28, 2018
Total rent expense	$ 91.3	$ 91.0	$ 91.0
Number of companies acquired	79	46	22	279
Aggregate amount of maximum earnout obligations related to acquisitions	462,300,000	384,800,000
Aggregate amount of maximum earnout obligations related to acquisitions, recorded in consolidated balance sheet	162,700,000	139,800,000
Liabilities recorded on self-insurance	9,000,000			9,000,000
Debt	36,500,000			36,500,000
Number of letters of credit issued	2
Income tax credits and adjustments	130,000,000
Tax-Advantaged Investments No Longer Held [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Total indemnifications	45,000,000			45,000,000
Errors and Omissions [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Insurance claims, amount retained	5,000,000
Amount of losses in excess of retained amounts	175,000,000			175,000,000
Self-Insurance Deductibles [Member] | Letter of Credit [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Debt	9,800,000			9,800,000
Rent-A-Captive Facility [Member] | Letter of Credit [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Debt	6,200,000			6,200,000
Maximum [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Ownership interest	50.00%			50.00%
Maximum [Member] | Errors and Omissions [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Actuarial range value	4,200,000			4,200,000
Minimum [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Ownership interest	1.00%			1.00%
Minimum [Member] | Errors and Omissions [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Actuarial range value	$ 1,600,000			$ 1,600,000