Acquisitions - Schedule of Pro Forma Financial Information (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Business Combinations [Abstract]
Revenue	$ 3,530,989	$ 3,456,656
Net income	103,594	(5,759)
Net income (loss) attributable to Granite	$ 92,263	$ (12,462)
Basic net income (loss) per share attributable to common shareholders	$ 2.00	$ (0.27)
Diluted net income (loss) per share attributable to common shareholders	$ 2.00	$ (0.27)