Note 4 - Revisions in Estimates - Summary of Impact of Revisions in Estimates to Gross Profit (Details) $ / shares in Units, $ in Thousands	3 Months Ended								9 Months Ended	12 Months Ended
	Dec. 31, 2021 USD ($) $ / shares	Sep. 30, 2021 USD ($) $ / shares	Jun. 30, 2021 USD ($) $ / shares	Mar. 31, 2021 USD ($) $ / shares	Dec. 31, 2020 USD ($) $ / shares	Sep. 30, 2020 USD ($) $ / shares	Jun. 30, 2020 USD ($) $ / shares	Mar. 31, 2020 USD ($) $ / shares	Sep. 30, 2021 USD ($)	Dec. 31, 2021 USD ($) $ / shares	Dec. 31, 2020 USD ($) $ / shares	Dec. 31, 2019 USD ($) $ / shares
Number of projects with upward estimate changes										2	0	0
Range of increase in gross profit from each project, net	$ 51,652	$ 101,960	$ 98,232	$ 53,712	$ 93,319	$ 113,015	$ 81,048	$ 17,271		$ 305,556	$ 304,653	$ 189,785
Increase to project profitability										9,496	(8,145)	40,224
Increase to net income/decrease to net loss attributable to Granite Construction Incorporated from continuing operations	$ 13,213	$ (35,043)	$ (54,461)	$ 66,195	$ (8,010)	$ 91,162	$ (3,405)	$ 65,370		$ (10,096)	$ 145,117	$ 60,191
Increase to net income/decrease to net loss per diluted share attributable to common shareholders from continuing operations (in dollars per share) | $ / shares	$ 0.28	$ (0.73)	$ (1.14)	$ 1.45	$ (0.17)	$ 1.97	$ (0.07)	$ 1.44		$ (0.22)	$ 3.14	$ 1.29
Number of projects with downward estimate changes										6	7	10
Range of reduction in gross profit from each project, net	$ (51,652)	$ (101,960)	$ (98,232)	$ (53,712)	$ (93,319)	$ (113,015)	$ (81,048)	$ (17,271)		$ (305,556)	$ (304,653)	$ (189,785)
Net income (loss)	$ (20,433)	$ 32,423	$ 55,747	$ (65,323)	$ 5,687	$ (98,357)	$ (973)	$ (72,538)		$ 2,414	$ (166,181)	$ (56,702)
Diluted earnings per share (in dollars per share) | $ / shares	$ (0.28)	$ 0.73	$ 1.14	$ (1.45)	$ 0.17	$ (1.97)	$ 0.07	$ (1.44)		$ 0.22	$ (3.14)	$ (1.29)
Estimated Due to Production at Higher Rate [Member]
Range of increase in gross profit from each project, net											$ 0	$ 0
Increase to project profitability										$ 15,400	0	0
Increase to net income/decrease to net loss attributable to Granite Construction Incorporated from continuing operations										$ 11,400	$ 0	$ 0
Increase to net income/decrease to net loss per diluted share attributable to common shareholders from continuing operations (in dollars per share) | $ / shares										$ 0.25	$ 0	$ 0
Range of reduction in gross profit from each project, net											$ 0	$ 0
Diluted earnings per share (in dollars per share) | $ / shares										$ (0.25)	$ (0)	$ (0)
Estimated Due to Production at Higher Rate [Member] | Minimum [Member]
Range of increase in gross profit from each project, net										$ 6,200
Range of reduction in gross profit from each project, net										(6,200)
Estimated Due to Production at Higher Rate [Member] | Maximum [Member]
Range of increase in gross profit from each project, net										9,200
Range of reduction in gross profit from each project, net										(9,200)
Estimated Cost Recovery of Customer Affirmative Claims and Back Charges [Member]
Range of increase in gross profit from each project, net									$ 70,600		$ 143,500	$ 199,100
Increase to project profitability										86,000	143,400	199,100
Increase to net income/decrease to net loss attributable to Granite Construction Incorporated from continuing operations										$ 48,600	$ 82,900	$ 140,500
Increase to net income/decrease to net loss per diluted share attributable to common shareholders from continuing operations (in dollars per share) | $ / shares										$ (1.06)	$ (1.79)	$ (3.02)
Range of reduction in gross profit from each project, net									$ (70,600)		$ (143,500)	$ (199,100)
Net income (loss)										$ 69,100	114,700	150,300
Amounts attributable to non-controlling interests										$ 20,500	$ 31,900	$ 9,800
Diluted earnings per share (in dollars per share) | $ / shares										$ 1.06	$ 1.79	$ 3.02
Estimated Cost Recovery of Customer Affirmative Claims and Back Charges [Member] | Minimum [Member]
Range of increase in gross profit from each project, net										$ (5,300)	$ (6,700)	$ (5,500)
Range of reduction in gross profit from each project, net										5,300	6,700	5,500
Estimated Cost Recovery of Customer Affirmative Claims and Back Charges [Member] | Maximum [Member]
Range of increase in gross profit from each project, net										(34,600)	(49,900)	(52,600)
Range of reduction in gross profit from each project, net										$ 34,600	$ 49,900	$ 52,600