Business Acquisitions - Summary of Purchase Price Attributable to Acquisitions (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Business Acquisition [Line Items]
Cash	$ 3,755	$ 1,527	$ 5,286
Restricted cash			629
Accounts receivable and contract assets	11,369	17,059	5,458
Other current assets	404	1,265	559
Current assets	15,528	19,851	11,932
Property and equipment	1,713	7,117	4,064
Operating lease right-of-use asset—net	3,079
Goodwill	37,277	147,609	36,622
Total assets	95,606	253,586	106,355
Current liabilities	6,079	9,721	6,001
Non- current liabilities			2,171
Operating lease liability—net of current portion	2,389
Total liabilities	8,468	9,721	8,172
Purchase price	87,138	243,865	98,183
Customer Relationships
Business Acquisition [Line Items]
Intangible assets	31,542	56,000	26,588
Trade Names
Business Acquisition [Line Items]
Intangible assets	3,465	4,200	1,667
Covenants Not to Compete
Business Acquisition [Line Items]
Intangible assets	2,681	4,109	5,443
Patent
Business Acquisition [Line Items]
Intangible assets			17,479
Acquired Technology
Business Acquisition [Line Items]
Intangible assets	321
Proprietary Software
Business Acquisition [Line Items]
Intangible assets		14,700	2,560
MSE Group
Business Acquisition [Line Items]
Cash	2,810
Accounts receivable and contract assets	2,980
Other current assets	31
Current assets	5,821
Property and equipment	513
Operating lease right-of-use asset—net	740
Goodwill	8,176
Total assets	25,413
Current liabilities	1,007
Operating lease liability—net of current portion	548
Total liabilities	1,555
Purchase price	23,858
MSE Group | Customer Relationships
Business Acquisition [Line Items]
Intangible assets	8,720
MSE Group | Trade Names
Business Acquisition [Line Items]
Intangible assets	521
MSE Group | Covenants Not to Compete
Business Acquisition [Line Items]
Intangible assets	922
EI
Business Acquisition [Line Items]
Cash	250
Accounts receivable and contract assets	4,675
Other current assets	84
Current assets	5,009
Property and equipment	32
Operating lease right-of-use asset—net	106
Goodwill	8,768
Total assets	25,687
Current liabilities	2,719
Operating lease liability—net of current portion	36
Total liabilities	2,755
Purchase price	22,932
EI | Customer Relationships
Business Acquisition [Line Items]
Intangible assets	10,265
EI | Trade Names
Business Acquisition [Line Items]
Intangible assets	996
EI | Covenants Not to Compete
Business Acquisition [Line Items]
Intangible assets	511
All Other 2021 Acquisitions
Business Acquisition [Line Items]
Cash	695
Accounts receivable and contract assets	3,714
Other current assets	289
Current assets	4,698
Property and equipment	1,168
Operating lease right-of-use asset—net	2,233
Goodwill	20,333
Total assets	44,506
Current liabilities	2,353
Operating lease liability—net of current portion	1,805
Total liabilities	4,158
Purchase price	40,348
All Other 2021 Acquisitions | Customer Relationships
Business Acquisition [Line Items]
Intangible assets	12,557
All Other 2021 Acquisitions | Trade Names
Business Acquisition [Line Items]
Intangible assets	1,948
All Other 2021 Acquisitions | Covenants Not to Compete
Business Acquisition [Line Items]
Intangible assets	1,248
All Other 2021 Acquisitions | Acquired Technology
Business Acquisition [Line Items]
Intangible assets	$ 321
CTEH
Business Acquisition [Line Items]
Cash		1,527
Accounts receivable and contract assets		17,059
Other current assets		1,265
Current assets		19,851
Property and equipment		7,042
Goodwill		146,983
Total assets		252,776
Current liabilities		9,721
Total liabilities		9,721
Purchase price		243,055
CTEH | Customer Relationships
Business Acquisition [Line Items]
Intangible assets		56,000
CTEH | Trade Names
Business Acquisition [Line Items]
Intangible assets		4,200
CTEH | Covenants Not to Compete
Business Acquisition [Line Items]
Intangible assets		4,000
CTEH | Proprietary Software
Business Acquisition [Line Items]
Intangible assets		14,700
All Other 2020 Acquisitions
Business Acquisition [Line Items]
Property and equipment		75
Goodwill		626
Total assets		810
Purchase price		810
All Other 2020 Acquisitions | Covenants Not to Compete
Business Acquisition [Line Items]
Intangible assets		$ 109
ECT2
Business Acquisition [Line Items]
Cash			3,149
Restricted cash			629
Accounts receivable and contract assets			1,707
Other current assets			498
Current assets			5,983
Property and equipment			776
Goodwill			16,395
Total assets			58,841
Current liabilities			5,024
Total liabilities			5,024
Purchase price			53,817
ECT2 | Customer Relationships
Business Acquisition [Line Items]
Intangible assets			13,840
ECT2 | Trade Names
Business Acquisition [Line Items]
Intangible assets			1,008
ECT2 | Covenants Not to Compete
Business Acquisition [Line Items]
Intangible assets			3,360
ECT2 | Patent
Business Acquisition [Line Items]
Intangible assets			17,479
All Other 2019 Acquisitions
Business Acquisition [Line Items]
Cash			2,137
Accounts receivable and contract assets			3,751
Other current assets			61
Current assets			5,949
Property and equipment			3,288
Goodwill			20,227
Total assets			47,514
Current liabilities			977
Non- current liabilities			2,171
Total liabilities			3,148
Purchase price			44,366
All Other 2019 Acquisitions | Customer Relationships
Business Acquisition [Line Items]
Intangible assets			12,748
All Other 2019 Acquisitions | Trade Names
Business Acquisition [Line Items]
Intangible assets			659
All Other 2019 Acquisitions | Covenants Not to Compete
Business Acquisition [Line Items]
Intangible assets			2,083
All Other 2019 Acquisitions | Proprietary Software
Business Acquisition [Line Items]
Intangible assets			$ 2,560