Commitments, Contingencies and Off-Balance Sheet Arrangements - Additional Information (Detail)	12 Months Ended			168 Months Ended
	Dec. 31, 2015 USD ($) ft² Entity Employees LetterOfCredit	Dec. 31, 2014 USD ($) Entity	Dec. 31, 2013 USD ($) Entity	Dec. 31, 2015 USD ($) ft² Entity
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Acquired property through lease area, sqft | ft²	306,000
Acquired property through lease percentage of building	60.00%
Operating lease commitment, expiration date	Feb. 28, 2018
Number of square feet | ft²	315,000			315,000
Number of employees will accommodate at new facility | Employees	1,750
Total rent expense	$ 121,600,000	$ 122,000,000	$ 91,300,000
Number of companies acquired | Entity	105	67	79	383
Aggregate amount of maximum earnout obligations related to acquisitions	$ 565,400,000	$ 549,800,000
Aggregate amount of maximum earnout obligations related to acquisitions, recorded in consolidated balance sheet	229,700,000	$ 205,300,000
Liabilities recorded on self-insurance	11,800,000			$ 11,800,000
Debt	62,800,000			62,800,000
Funding Commitments [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Expenditures related to our new business locations	$ 31,400,000
Self-Insurance Deductibles [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Number of letters of credit issued | LetterOfCredit	2
Rent-A-Captive Facility [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Number of letters of credit issued | LetterOfCredit	7
Letter of Credit [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Debt	$ 5,000,000			5,000,000
Number of letters of credit issued | LetterOfCredit	1
Letter of Credit [Member] | Security Deposit [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Debt	$ 500,000			500,000
Number of letters of credit issued | LetterOfCredit	1
Letter of Credit [Member] | Self-Insurance Deductibles [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Liabilities recorded on self-insurance	$ 9,700,000			9,700,000
Debt	11,800,000			11,800,000
Letter of Credit [Member] | Rent-A-Captive Facility [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Debt	$ 6,300,000			$ 6,300,000
Tax Increment Financing [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Property tax credit expect to receive period	15 years
Minimum [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Ownership interest	1.00%			1.00%
Minimum [Member] | Tax Increment Financing [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Property tax credit expect to receive	$ 60,000,000			$ 60,000,000
Maximum [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Ownership interest	50.00%			50.00%
Maximum [Member] | Tax Increment Financing [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Property tax credit expect to receive	$ 80,000,000			$ 80,000,000
Outstanding Purchase Obligations Related to New Corporate Headquarters [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Contractual Obligations, Payments Due by Period, Total	$ 81,600,000			$ 81,600,000