Business Acquisitions - Summary of Elements of Purchase Price of Acquisitions (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Cash	$ 175,450	$ 87,285	$ 48,961
Common Stock	25,000	4,047	5,634
Other Purchase Price Component Current	(1,889)	1,450	848
Other Purchase Price Component Long Term	100
Contingent Consideration Current	34,661
Contingent Consideration Long Term	10,543
Contingent Consideration		5,401	2,951
Total Purchase Price	243,865	98,183	58,394
CTEH
Business Acquisition [Line Items]
Cash	175,000
Common Stock	25,000
Other Purchase Price Component Current	(1,939)
Contingent Consideration Current	34,451
Contingent Consideration Long Term	10,543
Total Purchase Price	243,055
All Other Acquisitions
Business Acquisition [Line Items]
Cash	450	33,248
Common Stock		4,047
Other Purchase Price Component Current	50	1,670
Other Purchase Price Component Long Term	100
Contingent Consideration Current	210
Contingent Consideration		5,401
Total Purchase Price	$ 810	44,366
ECT2
Business Acquisition [Line Items]
Cash		54,037
Other Purchase Price Component Current		(220)
Total Purchase Price		$ 53,817
SES
Business Acquisition [Line Items]
Cash			450
Other Purchase Price Component Current			50
Total Purchase Price			500
FA
Business Acquisition [Line Items]
Cash			1,096
Other Purchase Price Component Current			360
Contingent Consideration			372
Total Purchase Price			1,828
AGC
Business Acquisition [Line Items]
Cash			7,400
Common Stock			925
Other Purchase Price Component Current			95
Contingent Consideration			871
Total Purchase Price			9,291
Streamline
Business Acquisition [Line Items]
Cash			5,678
Common Stock			631
Other Purchase Price Component Current			180
Total Purchase Price			6,489
Leymaster
Business Acquisition [Line Items]
Cash			2,465
Common Stock			435
Other Purchase Price Component Current			250
Contingent Consideration			434
Total Purchase Price			3,584
AES
Business Acquisition [Line Items]
Cash			21,877
Common Stock			2,028
Other Purchase Price Component Current			(16)
Contingent Consideration			1,274
Total Purchase Price			25,163
EPS
Business Acquisition [Line Items]
Cash			9,995
Common Stock			1,615
Other Purchase Price Component Current			(71)
Total Purchase Price			$ 11,539