Note 3 - Acquisitions - Schedule of Pro Forma Financial Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018
Revenue	$ 1,087,111	$ 2,638,664
Net income	39,550	81,151
Net income attributable to Granite	$ 37,477	$ 73,661
Basic net income per share attributable to common shareholders (in dollars per share)	$ 0.82	$ 1.61
Diluted net income per share attributable to common shareholders (in dollars per share)	$ 0.80	$ 1.60