Construction Joint Ventures - Income Statement Information (Details) - Joint Ventures - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Schedule of Equity Method Investments [Line Items]
Revenues	$ 43,466	$ 55,306	$ 70,312	$ 86,690
Income before tax	4,516	8,844	6,673	10,813
Sterling’s noncontrolling interest:
Revenues	19,377	25,971	32,459	41,655
Income before tax	$ 1,968	$ 3,116	$ 3,017	$ 4,100