Plateau Acquisition - Consideration Transferred and Purchase Price Allocation (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	Oct. 02, 2019	Jun. 30, 2020	Dec. 31, 2019	Oct. 01, 2019
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract]
Goodwill		$ 192,014	$ 191,892
Plateau Excavation
Business Acquisition [Line Items]
Cash consideration transferred, net of $2,425 of cash acquired	$ 375,000
Target working capital adjustment	21,323
Share consideration given for acquisitions	16,195
Note payable to seller	10,000
Tax basis election	5,015
Total consideration	427,533
Cash acquired	$ 2,425
Equity consideration transferred (in shares)	1,245
Business acquisition, price per share				$ 13.01
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract]
Accounts receivable, including retainage	$ 81,921
Costs and estimated earnings in excess of billings	974
Other current assets	249
Property and equipment, net	65,492
Other non-current assets, net	10
Accounts payable	(22,039)
Billings in excess of costs and estimated earnings	(16,540)
Other current and non-current liabilities	(7,918)
Total net tangible assets	102,149
Identifiable intangible assets	218,600
Goodwill	106,784
Total consideration transferred	$ 427,533