Business Acquisitions - Summary of Fair Values of Assets Acquired and Liabilities Assumed (Detail) - USD ($) $ in Thousands	4 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Nov. 30, 2018
Fair Values of Assets Acquired and Liabilities Assumed
Goodwill	$ 364,482	$ 359,045
Linetec
Fair Values of Assets Acquired and Liabilities Assumed
Cash and cash equivalents	3,900		$ 3,900
Accounts receivable	32,300		32,800
Revenue earned on contracts in progress in excess of billings	23,300		21,600
Prepaid expenses and other current assets	1,300		1,100
Property and equipment	88,900		89,400
Intangible assets	89,300		89,300
Goodwill	191,800		188,500
Total assets acquired	430,800		426,600
Accounts payable	8,000		8,000
Accrued liabilities	8,500		6,900
Deferred compensation and related accrued taxes	3,400		3,400
Redeemable noncontrolling interest	81,700		81,700
Total liabilities assumed and noncontrolling interest	101,600		100,000
Net assets acquired	329,200		$ 326,600
Measurement Period Adjustments
Accounts receivable, measurement period adjustments	(500)
Revenue earned on contracts in progress in excess of billings, measurement period adjustments	1,700
Prepaid expenses and other current assets, measurement period adjustments	200
Property and equipment, measurement period adjustments	(500)
Intangible assets, measurement period adjustments	0
Goodwill, measurement period adjustments	3,300
Total assets acquired, measurement period adjustments	4,200
Accrued liabilities, measurement period adjustments	1,600
Total liabilities assumed and noncontrolling interest, measurement period adjustments	1,600
Net assets acquired, measurement period adjustments	$ 2,600