Note 18 - Weighted Average Shares Outstanding and Net Income (Loss) Per Share - Reconciliation of the Weighted Average Shares Outstanding in Basic and Diluted Net Loss per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Net income (loss) from continuing operations allocated to common shareholders		$ 6,814	$ 31,023	$ 24,859	$ (63,273)	$ 4,836	$ 39,860	$ 8,023	$ (33,437)	$ (577)	$ 19,282	$ (31,425)
Net income (loss) attributable to Granite Construction Incorporated from discontinued operations										10,673	(164,399)	(28,766)
Net income (loss) allocated to common shareholders										$ 10,096	$ (145,117)	$ (60,191)
Weighted average common shares outstanding, basic (in shares)										45,788	45,614	46,559
Dilutive effect of RSUs and convertible notes (1)(2) (in shares)	[1],[2]									0	589	0
Weighted average common shares outstanding, diluted (in shares)										45,788	46,203	46,559
Basic continuing operations per share (in dollars per share)		$ 0.15	$ 0.68	$ 0.54	$ (1.38)	$ 0.11	$ 0.87	$ 0.18	$ (0.73)	$ (0.01)	$ 0.42	$ (0.67)
Basic discontinued operations per share (in dollars per share)		(0.44)	0.08	0.65	(0.07)	0.07	(2.87)	(0.11)	(0.71)	0.23	(3.60)	(0.62)
Basic earnings per share (in dollars per share)		(0.29)	0.76	1.19	(1.45)	0.18	(2.00)	0.07	(1.44)	0.22	(3.18)	(1.29)
Diluted continuing operations per share (in dollars per share)		0.14	0.65	0.52	(1.38)	0.10	0.86	0.17	(0.73)	(0.01)	0.42	(0.67)
Diluted discontinued operations per share (in dollars per share)		(0.42)	0.08	0.62	(0.07)	0.07	(2.83)	(0.10)	(0.71)	0.23	(3.56)	(0.62)
Diluted earnings per share (in dollars per share)		$ (0.28)	$ 0.73	$ 1.14	$ (1.45)	$ 0.17	$ (1.97)	$ 0.07	$ (1.44)	$ 0.22	$ (3.14)	$ (1.29)

[1] Due to the net losses from continuing operations for the years ended December 31, 2021 and 2019, RSUs representing approximately 533,000 and 388,000 shares, respectively, have been excluded from the number of shares used in calculating diluted net income (loss) per share, as their inclusion would be antidilutive.

[2] The number of shares used in calculating diluted net income (loss) per share for the year ended December 31, 2021 excluded the potential dilution from the 2.75% Convertible Notes converting into shares of common stock due to the net loss from continuing operations for the period. The number of shares used in calculating diluted net income per share for the years ended December 31, 2020 and 2019 excluded potential dilution from the 2.75% Convertible Notes converting into shares of common stock since the average stock price did not exceed $31.47. (See Note 14 for further details).