Note 3 - Restatement - Effects of Restatement (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Cash and cash equivalents	$ 288,922	$ 144,958	$ 288,922	$ 144,958		$ 262,273
Short-term marketable securities	0	41,037	0	41,037		27,799
Receivables, net ($31,978, $29,564 and $31,656 related to CCJVs)	596,922	564,543	596,922	564,543		547,417
Contract assets ($26,075, $25,034 and $17,371 related to CCJVs)	191,919	224,389	191,919	224,389		211,441
Inventories	105,023	101,686	105,023	101,686		88,885
Equity in construction joint ventures	183,542	220,247	183,542	220,247		193,110
Other current assets ($14,392, $13,350 and $11,440 related to CCJVs)	57,614	80,560	57,614	80,560		46,016
Total current assets	1,423,942	1,377,420	1,423,942	1,377,420		1,376,941
Property and equipment, net ($27,256, $31,136 and $31,560 related to CCJVs)	540,053	558,378	540,053	558,378		542,297
Long-term marketable securities	5,896	20,000	5,896	20,000		5,000
Investments in affiliates	74,511	82,109	74,511	82,109		84,176
Goodwill	248,690	264,107	248,690	264,107		264,279
Right of use assets	72,244	73,439	72,244	73,439		72,534
Deferred income taxes, net	40,926	28,249	40,926	28,249		50,158
Other noncurrent assets	102,392	120,915	102,392	120,915		106,703
Total assets	2,508,654	2,524,617	2,508,654	2,524,617		2,502,088
Current maturities of long-term debt	8,253	48,397	8,253	48,397		8,244
Accounts payable ($56,315, $57,795 and $50,338 related to CCJVs)	358,401	302,651	358,401	302,651		400,775
Contract liabilities ($69,688, $20,994 and $28,702 related to CCJVs)	159,818	128,443	159,818	128,443		95,737
Accrued expenses and other current liabilities ($4,179, $2,415 and $4,311 related to CCJVs)	363,128	360,231	363,128	360,231		337,300
Total current liabilities	889,600	839,722	889,600	839,722		842,056
Long-term debt	405,770	366,896	405,770	366,896		356,108
Long-term lease liabilities	56,071	60,868	56,071	60,868		58,618
Deferred income taxes, net	3,335	4,680	3,335	4,680		3,754
Other long-term liabilities	63,118	58,268	63,118	58,268		63,136
Commitments and contingencies (Note 18)
Preferred stock, $0.01 par value, authorized 3,000,000 shares, none outstanding		0		0
Common stock, $0.01 par value, authorized 150,000,000 shares; issued and outstanding: 45,651,914 shares as of June 30, 2020, 45,503,805 shares as of December 31, 2019 and 46,838,199 shares as of June 30, 2019	458	468	458	468		456
Additional paid-in capital	553,038	568,264	553,038	568,264		549,307
Accumulated other comprehensive loss	(5,800)	(2,187)	(5,800)	(2,187)		(2,645)
Retained earnings	520,025	579,920	520,025	579,920		594,353
Total Granite Construction Incorporated shareholders’ equity	1,067,721	1,146,465	1,067,721	1,146,465		1,141,471
Non-controlling interests	23,039	47,718	23,039	47,718		36,945
Total equity	1,090,760	1,194,183	1,090,760	1,194,183	$ 1,099,804	1,178,416	$ 1,224,519	$ 1,289,354
Total liabilities and equity	2,508,654	2,524,617	2,508,654	2,524,617		$ 2,502,088
Total revenue	915,771	866,092	1,551,698	1,447,905
Total cost of revenue	827,428	819,334	1,439,556	1,400,009
Gross (loss) profit	88,343	46,758	112,142	47,896
Selling, general and administrative expenses	91,682	70,998	170,063	151,153
Acquisition and integration expenses	0	9,177	0	11,025
Gain on sales of property and equipment	(1,190)	(4,935)	(1,813)	(6,835)
Operating loss	(2,149)	(28,482)	(80,521)	(107,447)
Interest income	(767)	(1,728)	(2,058)	(4,544)
Interest expense	6,549	4,158	11,543	8,172
Equity in income of affiliates, net	(2,016)	(2,594)	(2,062)	(3,884)
Other (income) expense, net	(3,160)	(759)	2,059	(2,521)
Total other income	606	(923)	9,482	(2,777)
Loss before benefit from income taxes	(2,755)	(27,559)	(90,003)	(104,670)
Benefit from income taxes	(1,782)	(5,913)	(16,492)	(23,263)
Net income (loss)	(973)	(21,646)	(73,511)	(81,407)
Amount attributable to non-controlling interests	4,378	(2,596)	11,546	(5,305)
Net loss attributable to Granite Construction Incorporated	$ 3,405	$ (24,242)	$ (61,965)	$ (86,712)
Basic (in dollars per share)	$ 0.07	$ (0.52)	$ (1.36)	$ (1.85)
Increase to net loss per diluted share (in dollars per share)	$ 0.07	$ (0.52)	$ (1.36)	$ (1.85)
Basic (in shares)	45,620	46,824	45,570	46,762
Diluted (in shares)	46,281	46,824	45,570	46,762
Net loss			$ (73,511)	$ (81,407)
Depreciation, depletion and amortization			57,269	61,747
Gain on sales of property and equipment, net			(1,813)	(6,835)
Deferred income taxes				(3)
Stock-based compensation			3,936	7,221
Equity in net loss from unconsolidated joint ventures			30,506	72,835
Net income from affiliates				(3,884)
Other non-cash adjustments			1,832	4,627
Receivables			(35,486)	(79,090)
Contract assets, net			83,065	(20,426)
Inventories			(16,138)	(12,329)
Contributions to unconsolidated construction joint ventures and affiliates			(24,223)	(45,500)
Distributions from unconsolidated construction joint ventures and affiliates			7,146	830
Other assets, net			(14,603)	(32,785)
Accounts payable			(44,103)	42,477
Accrued expenses and other current liabilities, net			12,000	(996)
Net cash used in operating activities			12,483	(93,515)
Transportation [Member]
Total revenue	$ 535,101	$ 481,746	886,002	783,710
Total cost of revenue	503,904	481,247	829,436	799,559
Water [Member]
Total revenue	109,724	112,070	211,381	211,152
Total cost of revenue	97,145	101,568	189,455	192,704
Specialty [Member]
Total revenue	174,914	174,629	307,953	313,753
Total cost of revenue	149,634	152,874	293,392	278,700
Materials [Member]
Total revenue	96,032	97,647	146,362	139,290
Total cost of revenue	$ 76,745	83,645	$ 127,273	129,046
Previously Reported [Member]
Cash and cash equivalents		144,958		144,958
Short-term marketable securities		41,037		41,037
Receivables, net ($31,978, $29,564 and $31,656 related to CCJVs)		551,958		551,958
Contract assets ($26,075, $25,034 and $17,371 related to CCJVs)		257,650		257,650
Inventories		102,163		102,163
Equity in construction joint ventures		241,786		241,786
Other current assets ($14,392, $13,350 and $11,440 related to CCJVs)		63,056		63,056
Total current assets		1,402,608		1,402,608
Property and equipment, net ($27,256, $31,136 and $31,560 related to CCJVs)		557,118		557,118
Long-term marketable securities		20,000		20,000
Investments in affiliates		82,109		82,109
Goodwill		264,107		264,107
Right of use assets		73,439		73,439
Deferred income taxes, net		36,055		36,055
Other noncurrent assets		122,705		122,705
Total assets		2,558,141		2,558,141
Current maturities of long-term debt		48,397		48,397
Accounts payable ($56,315, $57,795 and $50,338 related to CCJVs)		303,128		303,128
Contract liabilities ($69,688, $20,994 and $28,702 related to CCJVs)		119,289		119,289
Accrued expenses and other current liabilities ($4,179, $2,415 and $4,311 related to CCJVs)		339,047		339,047
Total current liabilities		809,861		809,861
Long-term debt		366,896		366,896
Long-term lease liabilities		60,868		60,868
Deferred income taxes, net		4,680		4,680
Other long-term liabilities		58,268		58,268
Commitments and contingencies (Note 18)
Preferred stock, $0.01 par value, authorized 3,000,000 shares, none outstanding		0		0
Common stock, $0.01 par value, authorized 150,000,000 shares; issued and outstanding: 45,651,914 shares as of June 30, 2020, 45,503,805 shares as of December 31, 2019 and 46,838,199 shares as of June 30, 2019		468		468
Additional paid-in capital		568,264		568,264
Accumulated other comprehensive loss		(3,448)		(3,448)
Retained earnings		642,124		642,124
Total Granite Construction Incorporated shareholders’ equity		1,207,408		1,207,408
Non-controlling interests		50,160		50,160
Total equity		1,257,568		1,257,568
Total liabilities and equity		2,558,141		2,558,141
Total revenue		789,540		1,409,341
Total cost of revenue		841,944		1,421,267
Gross (loss) profit		(52,404)		(11,926)
Selling, general and administrative expenses		69,998		151,153
Acquisition and integration expenses		9,177		12,500
Gain on sales of property and equipment		(4,935)		(6,835)
Operating loss		(126,644)		(168,744)
Interest income		(1,728)		(4,544)
Interest expense		4,158		8,172
Equity in income of affiliates, net		(2,594)		(3,884)
Other (income) expense, net		(759)		(2,521)
Total other income		(923)		(2,777)
Loss before benefit from income taxes		(125,721)		(165,967)
Benefit from income taxes		(31,760)		(40,925)
Net income (loss)		(93,961)		(125,042)
Amount attributable to non-controlling interests		(3,875)		(7,368)
Net loss attributable to Granite Construction Incorporated		$ (97,836)		$ (132,410)
Basic (in dollars per share)		$ (2.09)		$ (2.83)
Increase to net loss per diluted share (in dollars per share)		$ (2.09)		$ (2.83)
Basic (in shares)		46,824		46,762
Diluted (in shares)		46,824		46,762
Net loss				$ (125,042)
Depreciation, depletion and amortization				61,747
Gain on sales of property and equipment, net				(6,835)
Deferred income taxes				(35,192)
Stock-based compensation				7,221
Equity in net loss from unconsolidated joint ventures				105,834
Net income from affiliates				(3,884)
Other non-cash adjustments				4,630
Receivables				(78,081)
Contract assets, net				(23,775)
Inventories				(12,905)
Contributions to unconsolidated construction joint ventures and affiliates				(45,500)
Distributions from unconsolidated construction joint ventures and affiliates				830
Other assets, net				(15,361)
Accounts payable				48,230
Accrued expenses and other current liabilities, net				24,568
Net cash used in operating activities				(93,515)
Previously Reported [Member] | Transportation [Member]
Total revenue		$ 403,978		742,188
Total cost of revenue		503,857		820,817
Previously Reported [Member] | Water [Member]
Total revenue		112,831		212,086
Total cost of revenue		101,568		192,704
Previously Reported [Member] | Specialty [Member]
Total revenue		175,084		315,777
Total cost of revenue		152,874		278,700
Previously Reported [Member] | Materials [Member]
Total revenue		97,647		139,290
Total cost of revenue		83,645		129,046
Revision of Prior Period, Adjustment [Member]
Cash and cash equivalents		0		0
Short-term marketable securities		0		0
Receivables, net ($31,978, $29,564 and $31,656 related to CCJVs)		10,567		10,567
Contract assets ($26,075, $25,034 and $17,371 related to CCJVs)		(30,286)		(30,286)
Inventories		0		0
Equity in construction joint ventures		(18,401)		(18,401)
Other current assets ($14,392, $13,350 and $11,440 related to CCJVs)		16,919		16,919
Total current assets		(21,201)		(21,201)
Property and equipment, net ($27,256, $31,136 and $31,560 related to CCJVs)		0		0
Long-term marketable securities		0		0
Investments in affiliates		0		0
Goodwill		0		0
Right of use assets		0		0
Deferred income taxes, net		(8,580)		(8,580)
Other noncurrent assets		0		0
Total assets		(29,781)		(29,781)
Current maturities of long-term debt		0		0
Accounts payable ($56,315, $57,795 and $50,338 related to CCJVs)		0		0
Contract liabilities ($69,688, $20,994 and $28,702 related to CCJVs)		9,154		9,154
Accrued expenses and other current liabilities ($4,179, $2,415 and $4,311 related to CCJVs)		21,184		21,184
Total current liabilities		30,338		30,338
Long-term debt		0		0
Long-term lease liabilities		0		0
Deferred income taxes, net		0		0
Other long-term liabilities		0		0
Commitments and contingencies (Note 18)
Preferred stock, $0.01 par value, authorized 3,000,000 shares, none outstanding		0		0
Common stock, $0.01 par value, authorized 150,000,000 shares; issued and outstanding: 45,651,914 shares as of June 30, 2020, 45,503,805 shares as of December 31, 2019 and 46,838,199 shares as of June 30, 2019		0		0
Additional paid-in capital		0		0
Accumulated other comprehensive loss		0		0
Retained earnings		(58,719)		(58,719)
Total Granite Construction Incorporated shareholders’ equity		(58,719)		(58,719)
Non-controlling interests		(1,400)		(1,400)
Total equity		(60,119)		(60,119)
Total liabilities and equity		(29,781)		(29,781)
Total revenue		75,527		47,335
Total cost of revenue		(22,610)		(16,402)
Gross (loss) profit		98,137		63,737
Selling, general and administrative expenses		0		0
Acquisition and integration expenses		0		0
Gain on sales of property and equipment		0		0
Operating loss		98,137		63,737
Interest income		0		0
Interest expense		0		0
Equity in income of affiliates, net		0		0
Other (income) expense, net		0		0
Total other income		0		0
Loss before benefit from income taxes		98,137		63,737
Benefit from income taxes		25,874		18,247
Net income (loss)		72,263		45,490
Amount attributable to non-controlling interests		1,341		1,400
Net loss attributable to Granite Construction Incorporated		$ 73,604		$ 46,890
Basic (in dollars per share)		$ 1.57		$ 1.00
Increase to net loss per diluted share (in dollars per share)		$ 1.57		$ 1.00
Basic (in shares)		46,824		46,762
Diluted (in shares)		46,824		46,762
Net loss				$ 45,490
Depreciation, depletion and amortization				0
Gain on sales of property and equipment, net				0
Deferred income taxes				35,189
Stock-based compensation				0
Equity in net loss from unconsolidated joint ventures				(60,073)
Net income from affiliates				0
Other non-cash adjustments				0
Receivables				0
Contract assets, net				(3,687)
Inventories				0
Contributions to unconsolidated construction joint ventures and affiliates				0
Distributions from unconsolidated construction joint ventures and affiliates				0
Other assets, net				(16,919)
Accounts payable				0
Accrued expenses and other current liabilities, net				0
Net cash used in operating activities				0
Revision of Prior Period, Adjustment [Member] | Transportation [Member]
Total revenue		$ 76,255		48,233
Total cost of revenue				(16,402)
Revision of Prior Period, Adjustment [Member] | Transportation [Member] | Accounting Standards Update 2016-02 [Member]
Total cost of revenue		(22,610)
Revision of Prior Period, Adjustment [Member] | Water [Member]
Total revenue		(728)		(898)
Total cost of revenue		0		0
Revision of Prior Period, Adjustment [Member] | Specialty [Member]
Total revenue		0		0
Total cost of revenue		0		0
Revision of Prior Period, Adjustment [Member] | Materials [Member]
Total revenue		0		0
Total cost of revenue		0		0
Other Adjustments [Member]
Cash and cash equivalents		0		0
Short-term marketable securities		0		0
Receivables, net ($31,978, $29,564 and $31,656 related to CCJVs)		2,018		2,018
Contract assets ($26,075, $25,034 and $17,371 related to CCJVs)		(2,975)		(2,975)
Inventories		(477)		(477)
Equity in construction joint ventures		(3,138)		(3,138)
Other current assets ($14,392, $13,350 and $11,440 related to CCJVs)		585		585
Total current assets		(3,987)		(3,987)
Property and equipment, net ($27,256, $31,136 and $31,560 related to CCJVs)		1,260		1,260
Long-term marketable securities		0		0
Investments in affiliates		0		0
Goodwill		0		0
Right of use assets		0		0
Deferred income taxes, net		774		774
Other noncurrent assets		(1,790)		(1,790)
Total assets		(3,743)		(3,743)
Current maturities of long-term debt		0		0
Accounts payable ($56,315, $57,795 and $50,338 related to CCJVs)		(477)		(477)
Contract liabilities ($69,688, $20,994 and $28,702 related to CCJVs)		0		0
Accrued expenses and other current liabilities ($4,179, $2,415 and $4,311 related to CCJVs)		0		0
Total current liabilities		(477)		(477)
Long-term debt		0		0
Long-term lease liabilities		0		0
Deferred income taxes, net		0		0
Other long-term liabilities		0		0
Commitments and contingencies (Note 18)
Preferred stock, $0.01 par value, authorized 3,000,000 shares, none outstanding		0		0
Common stock, $0.01 par value, authorized 150,000,000 shares; issued and outstanding: 45,651,914 shares as of June 30, 2020, 45,503,805 shares as of December 31, 2019 and 46,838,199 shares as of June 30, 2019		0		0
Additional paid-in capital		0		0
Accumulated other comprehensive loss		1,261		1,261
Retained earnings		(3,485)		(3,485)
Total Granite Construction Incorporated shareholders’ equity		(2,224)		(2,224)
Non-controlling interests		(1,042)		(1,042)
Total equity		(3,266)		(3,266)
Total liabilities and equity		(3,743)		(3,743)
Total revenue		1,025		(8,771)
Total cost of revenue		0		(4,856)
Gross (loss) profit		1,025		(3,915)
Selling, general and administrative expenses		1,000		0
Acquisition and integration expenses		0		(1,475)
Gain on sales of property and equipment		0		0
Operating loss		25		(2,440)
Interest income		0		0
Interest expense		0		0
Equity in income of affiliates, net		0		0
Other (income) expense, net		0		0
Total other income		0		0
Loss before benefit from income taxes		25		(2,440)
Benefit from income taxes		(27)		(585)
Net income (loss)		52		(1,855)
Amount attributable to non-controlling interests		(62)		663
Net loss attributable to Granite Construction Incorporated		$ (10)		$ (1,192)
Basic (in dollars per share)		$ (0.00)		$ (0.03)
Increase to net loss per diluted share (in dollars per share)		$ (0.00)		$ (0.03)
Basic (in shares)		46,824		46,762
Diluted (in shares)		46,824		46,762
Net loss				$ (1,855)
Depreciation, depletion and amortization				0
Gain on sales of property and equipment, net				0
Deferred income taxes				0
Stock-based compensation				0
Equity in net loss from unconsolidated joint ventures				27,074
Net income from affiliates				0
Other non-cash adjustments				0
Receivables				(1,009)
Contract assets, net				7,036
Inventories				576
Contributions to unconsolidated construction joint ventures and affiliates				0
Distributions from unconsolidated construction joint ventures and affiliates				0
Other assets, net				(505)
Accounts payable				(5,753)
Accrued expenses and other current liabilities, net				(25,564)
Net cash used in operating activities				0
Other Adjustments [Member] | Transportation [Member]
Total revenue		$ 1,513		(6,711)
Total cost of revenue		0		(4,856)
Other Adjustments [Member] | Water [Member]
Total revenue		(33)		(36)
Total cost of revenue		0		0
Other Adjustments [Member] | Specialty [Member]
Total revenue		(455)		(2,024)
Total cost of revenue		0		0
Other Adjustments [Member] | Materials [Member]
Total revenue		0		0
Total cost of revenue		$ 0		$ 0