Intangible Assets - Summary of Intangible Assets (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Finite Lived Intangible Assets [Line Items]
Gross carrying amount	$ 252,525	$ 243,085
Accumulated amortization	(131,380)	(114,697)
Customer Relationships
Finite Lived Intangible Assets [Line Items]
Gross carrying amount	191,305	183,445
Accumulated amortization	(90,384)	(77,016)
Trade Names
Finite Lived Intangible Assets [Line Items]
Gross carrying amount	52,061	51,361
Accumulated amortization	(37,638)	(36,082)
Subcontractor Relationships
Finite Lived Intangible Assets [Line Items]
Gross carrying amount	5,440	4,700
Accumulated amortization	(1,490)	(131)
Non-compete Agreements
Finite Lived Intangible Assets [Line Items]
Gross carrying amount	3,719	3,579
Accumulated amortization	$ (1,868)	$ (1,468)