Business Acquisitions - Summary of Purchase Price Attributable to Acquisitions (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Business Acquisition [Line Items]
Cash	$ 1,527	$ 5,286
Restricted cash		629
Accounts receivable	17,059	5,458
Other current assets	1,265	559
Current assets	19,851	11,932
Property and equipment	7,117	4,064
Goodwill	147,609	36,622
Total assets	253,586	106,355
Current liabilities	9,721	6,001
Non- current liabilities		2,171
Total liabilities	9,721	8,172
Purchase price	243,865	98,183
CTEH
Business Acquisition [Line Items]
Cash	1,527
Accounts receivable	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
All Other Acquisitions
Business Acquisition [Line Items]
Cash		2,137
Accounts receivable		3,751
Other current assets		61
Current assets		5,949
Property and equipment	75	3,288
Goodwill	626	20,227
Total assets	810	47,514
Current liabilities		977
Non- current liabilities		2,171
Total liabilities		3,148
Purchase price	810	44,366
ECT2
Business Acquisition [Line Items]
Cash		3,149
Restricted cash		629
Accounts receivable		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
Customer Relationships
Business Acquisition [Line Items]
Intangible assets	56,000	26,588
Customer Relationships | CTEH
Business Acquisition [Line Items]
Intangible assets	56,000
Customer Relationships | All Other Acquisitions
Business Acquisition [Line Items]
Intangible assets		12,748
Customer Relationships | ECT2
Business Acquisition [Line Items]
Intangible assets		13,840
Trade Names
Business Acquisition [Line Items]
Intangible assets	4,200	1,667
Trade Names | CTEH
Business Acquisition [Line Items]
Intangible assets	4,200
Trade Names | All Other Acquisitions
Business Acquisition [Line Items]
Intangible assets		659
Trade Names | ECT2
Business Acquisition [Line Items]
Intangible assets		1,008
Covenants Not to Compete
Business Acquisition [Line Items]
Intangible assets	4,109	5,443
Covenants Not to Compete | CTEH
Business Acquisition [Line Items]
Intangible assets	4,000
Covenants Not to Compete | All Other Acquisitions
Business Acquisition [Line Items]
Intangible assets	109	2,083
Covenants Not to Compete | ECT2
Business Acquisition [Line Items]
Intangible assets		3,360
Proprietary Software
Business Acquisition [Line Items]
Intangible assets	14,700	2,560
Proprietary Software | CTEH
Business Acquisition [Line Items]
Intangible assets	$ 14,700
Proprietary Software | All Other Acquisitions
Business Acquisition [Line Items]
Intangible assets		2,560
Patent
Business Acquisition [Line Items]
Intangible assets		17,479
Patent | ECT2
Business Acquisition [Line Items]
Intangible assets		$ 17,479