Acquisitions - Aggregate Consideration Paid or Payable and Allocation of Net Assets (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2021	Jun. 30, 2021	Dec. 31, 2020
Business Acquisition [Line Items]
Goodwill		$ 85,500
Acquisitions 2021
Business Acquisition [Line Items]
Cash paid or payable	$ 23,500
Value of Quanta common stock issued	0
Contingent consideration	0	0
Fair value of total consideration transferred or estimated to be transferred	23,500
Accounts receivable	1,111	1,111
Contract assets	0	0
Other current assets	5,740	5,740
Property and equipment	1,552	1,552
Other assets	0	0
Identifiable intangible assets	9,746	9,746
Contract liabilities	0	0
Other current liabilities	(4,841)	(4,841)
Deferred tax liabilities, net	(1,975)	(1,975)
Total identifiable net assets	11,333	11,333
Goodwill	12,167
Fair value of net assets acquired	$ 23,500	$ 23,500
Acquisitions 2020
Business Acquisition [Line Items]
Cash paid or payable			$ 359,575
Value of Quanta common stock issued			57,119
Contingent consideration			2,250
Fair value of total consideration transferred or estimated to be transferred			418,944
Accounts receivable			74,492
Contract assets			8,919
Other current assets			53,302
Property and equipment			143,276
Other assets			14
Identifiable intangible assets			96,827
Contract liabilities			(3,750)
Other current liabilities			(35,112)
Deferred tax liabilities, net			(3,185)
Total identifiable net assets			334,783
Goodwill			84,161
Fair value of net assets acquired			$ 418,944