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Commitments, Contingencies and Off-Balance Sheet Arrangements - Additional Information (Detail)		3 Months Ended		207 Months Ended
	Dec. 22, 2018 USD ($) Employee	Mar. 31, 2019 USD ($) ft² Employees Entity LetterOfCredit	Mar. 31, 2018 Entity	Mar. 31, 2019 USD ($) ft² Entity LetterOfCredit
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Number of square feet | ft²		360,000		360,000
Number of employees will accommodate at new facility | Employees		2,000
Number of companies acquired | Entity		33	39	518
Aggregate amount of maximum earnout obligations related to acquisitions		$ 618,900,000
Aggregate amount of maximum earnout obligations related to acquisitions, recorded in consolidated balance sheet		$ 293,600,000
Definitive Agreement [Member] | Stackhouse Poland Group Limited [Member] | United Kingdom, Pounds
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Cash consideration	$ 350,000,000
Number of employees will accommodate at new facility | Employee	500
Tax Increment Financing [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Property tax credit expect to receive period		15 years
Letter of Credit [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Debt		$ 1,300,000		$ 1,300,000
Number of letters of credit issued | LetterOfCredit		1		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		1
Letter of Credit [Member] | Self-Insurance Deductibles [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Debt		$ 10,200,000		$ 10,200,000
Liabilities recorded on self-insurance		$ 15,300,000		$ 15,300,000
Number of letters of credit issued | LetterOfCredit		2		2
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
Number of letters of credit issued | LetterOfCredit		7		7
Minimum [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Ownership interest		1.00%		1.00%
Maximum [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Ownership interest		50.00%		50.00%

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