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Commitments, Contingencies and Off-Balance Sheet Arrangements - Additional Information (Detail) |  | 12 Months Ended | 228 Months Ended
--- | --- | --- | ---
Dec. 23, 2020 USD ($) | Dec. 31, 2020 USD ($) ft² Employee Entity LetterOfCredit Company | Dec. 31, 2019 USD ($) Entity | Dec. 31, 2018 USD ($) Entity | Dec. 31, 2020 USD ($) ft² Entity LetterOfCredit
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items] |  |  |  |  |
Accrued Liability |  | $ 50,000,000.0 |  |  | $ 50,000,000.0
Cash Paid |  | $ 398,300,000 |  |  |
Number of square feet | ft² |  | 360,000 |  |  | 360,000
Number of employees will accommodate at new facility | Employee |  | 2,000 |  |  |
Total rent expense |  | $ 154,000,000.0 | $ 148,100,000 | $ 140,000,000.0 |
Number of companies acquired | Entity |  | 135 | 116 | 112 | 583
Aggregate amount of maximum earnout obligations related to acquisitions |  | $ 1,128,100,000 | $ 982,900,000 |  |
Aggregate amount of maximum earnout obligations related to acquisitions, recorded in consolidated balance sheet |  | 592,200,000 | $ 565,000,000.0 |  |
Aggregate amount of earnout obligation expected settlement in cash or stock at option |  | 493,700,000 |  |  | $ 493,700,000
Aggregate amount of earnout obligation expected settlement in cash |  | $ 98,500,000 |  |  | $ 98,500,000
Ownership interest |  | 50.00% |  |  | 50.00%
Debt |  | $ 19,600,000 |  |  | $ 19,600,000
Liabilities recorded on self-insurance |  | 17,500,000 |  |  | $ 17,500,000
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
Collateral [Member] |  |  |  |  |
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items] |  |  |  |  |
Number of letters of credit issued | LetterOfCredit |  | 1 |  |  | 1
Self-Insurance Deductibles [Member] |  |  |  |  |
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items] |  |  |  |  |
Number of letters of credit issued | LetterOfCredit |  | 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
Errors And Omissions [Member] | Up to $4.5 Million [Member] |  |  |  |  |
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items] |  |  |  |  |
Insurance claims, amount retained |  | $ 4,500,000 |  |  |
Errors And Omissions [Member] | Up to $10 Million [Member] |  |  |  |  |
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items] |  |  |  |  |
Insurance claims, amount retained |  | 10,000,000.0 |  |  |
Insurance claim arise during ordinary course of business |  | 10,000,000.0 |  |  | $ 10,000,000.0
Errors And Omissions [Member] | Up to $20.0 Million [Member] |  |  |  |  |
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items] |  |  |  |  |
Insurance claims, amount retained |  | 20,000,000.0 |  |  |
Errors And Omissions [Member] | Up to $27.0 Million [Member] |  |  |  |  |
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items] |  |  |  |  |
Insurance claims, amount retained |  | 27,000,000.0 |  |  |
Letter of Credit [Member] | Security Deposit [Member] |  |  |  |  |
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items] |  |  |  |  |
Debt |  | 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
Letter of Credit [Member] | Self-Insurance Deductibles [Member] |  |  |  |  |
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items] |  |  |  |  |
Debt |  | 9,400,000 |  |  | 9,400,000
Liabilities recorded on self-insurance |  | 17,500,000 |  |  | 17,500,000
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
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 |  | $ 2,600,000 |  |  | 2,600,000
Minimum [Member] | Errors And Omissions [Member] | Up to $4.5 Million [Member] |  |  |  |  |
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items] |  |  |  |  |
Insurance claim arise during ordinary course of business |  | 10,000,000.0 |  |  | 10,000,000.0
Minimum [Member] | Errors And Omissions [Member] | Up to $20.0 Million [Member] |  |  |  |  |
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items] |  |  |  |  |
Insurance claim arise during ordinary course of business |  | 100,000,000.0 |  |  | 100,000,000.0
Minimum [Member] | Errors And Omissions [Member] | Up to $27.0 Million [Member] |  |  |  |  |
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items] |  |  |  |  |
Insurance claim arise during ordinary course of business |  | $ 240,000,000.0 |  |  | $ 240,000,000.0
Minimum [Member] | Unconsolidated Investments in Enterprises [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%
Maximum [Member] | Errors And Omissions [Member] |  |  |  |  |
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items] |  |  |  |  |
Actuarial range value |  | $ 6,400,000 |  |  | $ 6,400,000
Maximum [Member] | Errors And Omissions [Member] | Up to $4.5 Million [Member] |  |  |  |  |
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items] |  |  |  |  |
Insurance claim arise during ordinary course of business |  | 100,000,000.0 |  |  | 100,000,000.0
Maximum [Member] | Errors And Omissions [Member] | Up to $20.0 Million [Member] |  |  |  |  |
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items] |  |  |  |  |
Insurance claim arise during ordinary course of business |  | 240,000,000.0 |  |  | 240,000,000.0
Maximum [Member] | Errors And Omissions [Member] | Up to $27.0 Million [Member] |  |  |  |  |
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items] |  |  |  |  |
Insurance claim arise during ordinary course of business |  | $ 350,000,000.0 |  |  | $ 350,000,000.0
Maximum [Member] | Unconsolidated Investments in Enterprises [Member] |  |  |  |  |
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items] |  |  |  |  |
Ownership interest |  | 50.00% |  |  | 50.00%
Tax Increment Financing [Member] |  |  |  |  |
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items] |  |  |  |  |
Property tax credits receivable period |  | 15 years |  |  |
Economic development for growing economy tax credit |  | $ 25,500,000 |  |  | $ 25,500,000
Tax Increment Financing [Member] | Minimum [Member] |  |  |  |  |
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items] |  |  |  |  |
Property tax credit expect to receive |  | 60,000,000.0 |  |  | 60,000,000.0
Tax Increment Financing [Member] | Maximum [Member] |  |  |  |  |
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items] |  |  |  |  |
Property tax credit expect to receive |  | 90,000,000.0 |  |  | 90,000,000.0
Ashton Tiffany, LLC (AT) [Member] |  |  |  |  |
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items] |  |  |  |  |
Accrued Liability |  | 48,200,000 |  |  | 48,200,000
Cash Paid |  | 48,300,000 |  |  |
Ashton Tiffany, LLC (AT) [Member] | Common Stock [Member] |  |  |  |  |
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items] |  |  |  |  |
Accrued Liability |  | $ 48,200,000 |  |  | $ 48,200,000
The Bollington Wilson Group [Member] |  |  |  |  |
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items] |  |  |  |  |
Percentage of equity interests acquired | 100.00% |  |  |  |
Cash Paid | $ 330,000,000.0 |  |  |  |

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