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Commitments, Contingencies and Off-Balance Sheet Arrangements - Additional Information (Detail) | 3 Months Ended | 9 Months Ended | 189 Months Ended
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Sep. 30, 2017 USD ($) ft² Entity | Sep. 30, 2016 Entity | Sep. 30, 2017 USD ($) ft² Entity Employees LetterOfCredit | Sep. 30, 2016 Entity | Sep. 30, 2017 USD ($) ft² Entity
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 | Employees |  |  | 2,000 |  |
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 companies acquired | Entity | 31 | 27 | 89 | 77 | 450
Aggregate amount of maximum earnout obligations related to acquisitions |  |  | $ 563,900,000 |  |
Aggregate amount of maximum earnout obligations related to acquisitions, recorded in consolidated balance sheet |  |  | $ 274,300,000 |  |
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 | $ 4,200,000 |  | $ 4,200,000 |  | $ 4,200,000
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 |  | 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 |  | 9,700,000
Debt | 12,400,000 |  | $ 12,400,000 |  | 12,400,000
Number of letters of credit issued | LetterOfCredit |  |  | 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 |  | $ 6,300,000
Number of letters of credit issued | LetterOfCredit |  |  | 7 |  |
Minimum [Member] |  |  |  |  |
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items] |  |  |  |  |
Ownership interest | 1.00% |  | 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 |  | $ 60,000,000
Maximum [Member] |  |  |  |  |
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items] |  |  |  |  |
Ownership interest | 50.00% |  | 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 |  | $ 80,000,000
Outstanding Purchase Obligations Related to New Corporate Headquarters Building [Member] |  |  |  |  |
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items] |  |  |  |  |
Contractual Obligations, Payments Due by Period, Total | $ 700,000 |  | $ 700,000 |  | $ 700,000

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