Basis of Presentation - Summary of Impact of Adoption of Accounting Standards (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Jan. 01, 2018	Dec. 31, 2017
Assets
Receivables, net	$ 618,070	$ 627,081	$ 618,070	$ 627,081		$ 479,791
Contract assets	213,989	0	213,989	0		0
Costs and estimated earnings in excess of billings	0	94,527	0	94,527		103,965
Deferred income taxes, net	6,408	0	6,408	0		0
Liabilities and equity
Contract liabilities	117,759	0	117,759	0	$ 83,674	0
Billings in excess of costs and estimated earnings	0	168,707	0	168,707		135,146
Accrued expenses and other current liabilities	296,033	246,775	296,033	246,775		236,407
Retained earnings	786,936	756,183	786,936	756,183		$ 783,699
Revenue
Revenue	1,055,591	957,126	2,426,089	2,188,439
Cost of revenue
Cost of revenue	911,100	842,596	2,144,946	1,974,213
Gross profit	144,491	114,530	281,143	214,226
Operating income	67,406	66,782	48,842	54,330
Provision for (benefit from) income taxes	8,692	21,249	7,357	16,841
Net income	59,097	48,055	43,354	40,476
Net income attributable to Granite Construction Incorporated	55,672	$ 45,982	35,864	$ 36,325
Transportation [Member]
Revenue
Revenue	610,847		1,472,703
Cost of revenue
Cost of revenue	539,871		1,334,302
Water [Member]
Revenue
Revenue	124,292		215,951
Cost of revenue
Cost of revenue	100,189		174,834
Specialty [Member]
Revenue
Revenue	190,836		461,149
Cost of revenue
Cost of revenue	162,737		395,838
Materials [Member]
Revenue
Revenue	129,616		276,286
Cost of revenue
Cost of revenue	108,303		239,972
Accounting Standards Update 2014-09 [Member] | Balances Without Adoption of Topic 606 [Member]
Assets
Receivables, net	733,368		733,368
Contract assets	0		0
Costs and estimated earnings in excess of billings	141,525		141,525
Deferred income taxes, net	1,136		1,136
Liabilities and equity
Contract liabilities	0		0
Billings in excess of costs and estimated earnings	158,228		158,228
Accrued expenses and other current liabilities	286,681		286,681
Retained earnings	793,381		793,381
Revenue
Revenue	1,049,164		2,419,673
Cost of revenue
Cost of revenue	913,163		2,150,087
Gross profit	136,001		269,585
Operating income	58,916		37,284
Provision for (benefit from) income taxes	6,603		4,554
Net income	52,697		34,599
Net income attributable to Granite Construction Incorporated	49,272		27,109
Accounting Standards Update 2014-09 [Member] | Balances Without Adoption of Topic 606 [Member] | Transportation [Member]
Revenue
Revenue	607,413		1,468,253
Cost of revenue
Cost of revenue	541,934		1,339,443
Accounting Standards Update 2014-09 [Member] | Balances Without Adoption of Topic 606 [Member] | Water [Member]
Revenue
Revenue	119,977		213,157
Cost of revenue
Cost of revenue	100,189		174,834
Accounting Standards Update 2014-09 [Member] | Balances Without Adoption of Topic 606 [Member] | Specialty [Member]
Revenue
Revenue	192,158		461,977
Cost of revenue
Cost of revenue	162,737		395,838
Accounting Standards Update 2014-09 [Member] | Balances Without Adoption of Topic 606 [Member] | Materials [Member]
Revenue
Revenue	129,616		276,286
Cost of revenue
Cost of revenue	108,303		239,972
Accounting Standards Update 2014-09 [Member] | Effect of Change Higher/(Lower) [Member]
Assets
Receivables, net	(115,298)		(115,298)
Contract assets	213,989		213,989
Costs and estimated earnings in excess of billings	(141,525)		(141,525)
Deferred income taxes, net	5,272		5,272
Liabilities and equity
Contract liabilities	117,759		117,759
Billings in excess of costs and estimated earnings	(158,228)		(158,228)
Accrued expenses and other current liabilities	9,352		9,352
Retained earnings	(6,445)		(6,445)
Revenue
Revenue	6,427		6,416
Cost of revenue
Cost of revenue	(2,063)		(5,141)
Gross profit	8,490		11,558
Operating income	8,490		11,558
Provision for (benefit from) income taxes	2,089		2,803
Net income	6,400		8,755
Net income attributable to Granite Construction Incorporated	6,400		8,755
Accounting Standards Update 2014-09 [Member] | Effect of Change Higher/(Lower) [Member] | Transportation [Member]
Revenue
Revenue	3,434		4,450
Cost of revenue
Cost of revenue	(2,063)		(5,141)
Accounting Standards Update 2014-09 [Member] | Effect of Change Higher/(Lower) [Member] | Water [Member]
Revenue
Revenue	4,315		2,794
Cost of revenue
Cost of revenue	0		0
Accounting Standards Update 2014-09 [Member] | Effect of Change Higher/(Lower) [Member] | Specialty [Member]
Revenue
Revenue	(1,322)		(828)
Cost of revenue
Cost of revenue	0		0
Accounting Standards Update 2014-09 [Member] | Effect of Change Higher/(Lower) [Member] | Materials [Member]
Revenue
Revenue	0		0
Cost of revenue
Cost of revenue	$ 0		$ 0