Acquisitions - Schedule of Pro Forma Financial Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Business Combinations [Abstract]
Revenue	$ 909,783	$ 888,176	$ 1,583,073	$ 1,452,067
Net income (loss)	16,834	(10,974)	14,454	(61,709)
Net income (loss) attributable to Granite	$ 14,530	$ (13,113)	$ 10,389	$ (63,787)
Basic net income (loss) per share attributable to common shareholders	$ 0.32	$ (0.29)	$ 0.23	$ (1.41)
Diluted net income (loss) per share attributable to common shareholders	$ 0.30	$ (0.29)	$ 0.22	$ (1.41)