BUSINESS ACQUISITIONS - Estimated Fair Values of Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Business Acquisition [Line Items]
Goodwill	$ 308,880	$ 261,767
2021 Acquisitions
Business Acquisition [Line Items]
Cash	34
Accounts receivable	5,011
Other receivables	1,291
Costs in excess of billings	3,003
Goodwill	47,203
Property and equipment	214
Other assets	2,460
Assets acquired	75,475
Current liabilities assumed	(10,134)
Contingent consideration	(301)
Net assets acquired	65,040
2021 Acquisitions \| Non-compete agreements
Business Acquisition [Line Items]
Finite-lived intangibles	1,040
2021 Acquisitions \| Customer relationships
Business Acquisition [Line Items]
Finite-lived intangibles	$ 15,219

Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Contract With Customer, Assets

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Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Current Assets, Other Receivables

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Amount of assets acquired at the acquisition date.

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Amount of currency on hand as well as demand deposits with banks or financial institutions, acquired at the acquisition date. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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The amount of liability arising from an inherited contingency (as defined) which has been recognized as of the acquisition date.

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Amount due from customers or clients for goods or services, including trade receivables, that have been delivered or sold in the normal course of business, and amounts due from others, including related parties expected to be converted to cash, sold or exchanged within one year or the normal operating cycle, if longer, acquired at the acquisition date.

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Amount of liabilities due within one year or within the normal operating cycle, if longer, assumed at the acquisition date.

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The amount of identifiable intangible assets recognized as of the acquisition date.

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Amount recognized as of the acquisition date for the identifiable assets acquired in excess of (less than) the aggregate liabilities assumed.

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Amount of other assets expected to be realized or consumed after one year or the normal operating cycle, if longer, acquired at the acquisition date.

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The amount of property, plant, and equipment recognized as of the acquisition date.

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Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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