Note 10 - Construction Joint Ventures - Schedule of Unconsolidated Construction Joint Ventures Revenue and Costs (Details) - USD ($) $ in Thousands		3 Months Ended						12 Months Ended
		Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cost of revenue		$ 989,556	$ 819,334	$ 580,675	$ 910,238	$ 728,889	$ 507,432	$ 3,223,928	$ 2,952,191	$ 2,679,633
Collaborative Arrangement [Member]
Revenue								421,360	514,475	560,907
Cost of revenue								542,672	561,596	605,892
Granite’s interest in gross loss								(121,312)	(47,121)	(44,985)
Collaborative Arrangement [Member] | Corporate Joint Venture [Member]
Revenue								1,471,157	1,544,406	2,057,336
Cost of revenue								1,900,524	1,787,501	1,995,915
Collaborative Arrangement [Member] | Co-venturer [Member] | Other Partners Interest in Partnerships [Member]
Revenue	[1]							1,049,797	1,029,931	1,496,429
Cost of revenue	[1]							$ 1,357,852	$ 1,225,905	$ 1,390,023

[1] Partners' interest and adjustments includes amounts to reconcile total revenue and total cost of revenue as reported by our partners to Granite's interest adjusted to reflect our accounting policies and estimates primarily related to contract forecast differences.