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Commitments, Contingencies and Off-Balance Sheet Arrangements - Additional Information (Detail) | 3 Months Ended | 9 Months Ended | 225 Months Ended
--- | --- | --- | ---
Sep. 30, 2020 USD ($) ft² Entity LetterOfCredit | Sep. 30, 2019 Entity | Sep. 30, 2020 USD ($) ft² Entity Employee LetterOfCredit Company | Sep. 30, 2019 Entity | Sep. 30, 2020 USD ($) ft² Entity LetterOfCredit
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items] |  |  |  |  |
Number of square feet | ft² | 360,000 |  | 360,000 |  | 360,000
Number of employees will accommodate at new facility | Employee |  |  | 2,000 |  |
Number of companies acquired | Entity | 55 | 29 | 126 | 86 | 573
Aggregate amount of maximum earnout obligations related to acquisitions |  |  | $ 1,026,100,000 |  |
Aggregate amount of maximum earnout obligations related to acquisitions, recorded in consolidated balance sheet |  |  | 502,500,000 |  |
Income tax credits and adjustments |  |  | $ 108,000,000.0 |  |
Security Deposit [Member] |  |  |  |  |
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items] |  |  |  |  |
Number of letters of credit issued | LetterOfCredit | 1 |  | 1 |  | 1
Collateral [Member] |  |  |  |  |
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items] |  |  |  |  |
Number of letters of credit issued | LetterOfCredit | 1 |  | 1 |  | 1
Self-Insurance Deductibles [Member] |  |  |  |  |
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items] |  |  |  |  |
Number of letters of credit issued | LetterOfCredit | 2 |  | 2 |  | 2
Rent-A-Captive Facility [Member] |  |  |  |  |
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items] |  |  |  |  |
Number of letters of credit issued | LetterOfCredit | 7 |  | 7 |  | 7
Errors And Omissions [Member] |  |  |  |  |
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items] |  |  |  |  |
Insurance claims, amount retained |  |  | $ 10,000,000.0 |  |
Amount of losses in excess of retained amounts | $ 350,000,000.0 |  | 350,000,000.0 |  | $ 350,000,000.0
Letter of Credit [Member] | Security Deposit [Member] |  |  |  |  |
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items] |  |  |  |  |
Debt | 500,000 |  | 500,000 |  | 500,000
Letter of Credit [Member] | Collateral [Member] |  |  |  |  |
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items] |  |  |  |  |
Debt | 1,000,000.0 |  | 1,000,000.0 |  | 1,000,000.0
Letter of Credit [Member] | Self-Insurance Deductibles [Member] |  |  |  |  |
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items] |  |  |  |  |
Debt | 9,400,000 |  | 9,400,000 |  | 9,400,000
Liabilities recorded on self-insurance | 17,300,000 |  | 17,300,000 |  | 17,300,000
Letter of Credit [Member] | Rent-A-Captive Facility [Member] |  |  |  |  |
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items] |  |  |  |  |
Debt | 7,500,000 |  | $ 7,500,000 |  | 7,500,000
Minimum [Member] |  |  |  |  |
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items] |  |  |  |  |
Number of micro-captive insurance companies organized or managed | Company |  |  | 100 |  |
Minimum [Member] | Errors And Omissions [Member] |  |  |  |  |
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items] |  |  |  |  |
Actuarial range value | 3,700,000 |  | $ 3,700,000 |  | 3,700,000
Maximum [Member] | Errors And Omissions [Member] |  |  |  |  |
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items] |  |  |  |  |
Actuarial range value | $ 5,100,000 |  | $ 5,100,000 |  | $ 5,100,000
Unconsolidated Investments in Enterprises [Member] | Minimum [Member] |  |  |  |  |
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items] |  |  |  |  |
Ownership interest | 1.00% |  | 1.00% |  | 1.00%
Unconsolidated Investments in Enterprises [Member] | Maximum [Member] |  |  |  |  |
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items] |  |  |  |  |
Ownership interest | 50.00% |  | 50.00% |  | 50.00%

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