Document And Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2020	Mar. 25, 2021	Jun. 30, 2020
Document Information [Line Items]
Entity Central Index Key	0000861459
Entity Registrant Name	GRANITE CONSTRUCTION INC
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Period Focus	FY
Document Fiscal Year Focus	2020
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Document Transition Report	false
Entity File Number	1-12911
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	77-0239383
Entity Address, Address Line One	585 West Beach Street
Entity Address, City or Town	Watsonville
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	95076
City Area Code	831
Local Phone Number	724-1011
Title of 12(b) Security	Common stock, $0.01 par value
Trading Symbol	GVA
Security Exchange Name	NYSE
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 855,200,000
Entity Common Stock, Shares Outstanding		45,789,095