Entity tax identification number Entity Tax Identification Number EBP 001 EBP 001 [Member] EBP 001 Maximum Maximum [Member] Legal Entity [Axis] Legal Entity [Axis] Statistical Measurement [Domain] Statistical Measurement [Domain] EBP, Description of Plan [Table] EBP, Description of Plan [Table] Mutual funds Mutual Funds Mutual Fund [Member] Subsequent Event Subsequent Event [Member] Sold value EBP, Investment Sold, Excluding Plan Interest in Master Trust, Selling Price EBP, Related Party and Party-in-Interest Transactions [Table] EBP, Related Party and Party-in-Interest Transactions [Table] Percentage of employee pre-tax contributions of gross pay EBP, Participant Contribution, Pretax, Maximum Annual Compensation to Total Compensation, Percentage Total deductions EBP, Change in Net Asset Available for Benefit, Decrease Maximum borrowing amount EBP, Note Receivable from Participant, Account, Maximum Borrowing, Amount Fair Value Measurements EBP, Investment, Fair Value and NAV [Text Block] Minimum borrowing amount EBP, Note Receivable from Participant, Account, Minimum Borrowing, Amount Total investments Fair Value EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value Subsequent Event Type [Domain] Subsequent Event Type [Domain] Percentage of employee after-tax Roth contributions EBP, Participant Contribution, After Tax, Maximum Annual Contribution to Eligible Compensation, Percentage EBP, Participant Contribution, After Tax, Maximum Annual Contribution to Eligible Compensation, Percentage Level 1 Fair Value, Inputs, Level 1 [Member] Basis spread on variable rate EBP, Participant Loan, Basis Spread On Variable Rate EBP, Participant Loan, Basis Spread On Variable Rate EBP, Investment, Fair Value and NAV [Abstract] Vesting of benefits (in years) EBP, Employer Contribution Vesting Service Period Minimum Vesting service period for company contribution and/ or investment earning to the participant in Company Matching Contributions, Fixed Rate Contributions, Discretionary Profit-Sharing Contributions, Qualified Non-Elective Contributions, and Disability Contributions. Aggregate Investment in Common Stock EBP, Related Party and Party-in-Interest Transactions [Table Text Block] Assets EBP, Asset [Abstract] Statistical Measurement [Axis] Statistical Measurement [Axis] Additions: EBP, Change in Net Asset Available for Benefit, Increase [Abstract] EBP, Statement of Change in Net Asset Available for Benefit [Table] EBP, Statement of Change in Net Asset Available for Benefit [Table] Assets transferred into plan EBP, Change in Net Asset Available for Benefit, Transfer to (from) Plan Distributions to participants or beneficiaries EBP, Payment to Participant [Policy Text Block] Term after hire date for automatic enrollment (in days) EBP, Participant Contribution, Automatic Enrollment, Term After Hire Date EBP, Participant Contribution, Automatic Enrollment, Term After Hire Date Amendment Flag Amendment Flag Employee contributions, including rollovers EBP, Change in Net Asset Available for Benefit, Increase from Participant Contribution Basis of accounting EBP, Basis of Accounting [Policy Text Block] EBP, Schedule of Asset Held for Investment [Table] EBP, Schedule of Asset Held for Investment [Table] EBP, Plan Termination [Table] EBP, Plan Termination [Table] EBP, Plan Termination [Table] Investment rate EBP, Investment, Interest Rate Number of Shares (in shares) EBP, Investment, Number of Shares EBP, Description of Plan and Accounting Change [Abstract] Fair Value of Investments EBP, Investment, Fair Value and NAV [Table Text Block] Total Company common stock held EBP, Employer, Common Stock Fund And Employee Stock Ownership Plan, Common, Shares [Member] EBP, Employer, Common Stock Fund And Employee Stock Ownership Plan, Common, Shares Borrowing term (in years) EBP, Note Receivable From Participant, Borrowing Term EBP, Note Receivable From Participant, Borrowing Term Granite ESOP Stock Fund Employee Stock Ownership Plan, Common, Shares [Member] Common stock Common Stock Common Stock [Member] Investments [Domain] Investments [Domain] Use of estimates EBP, Use of Estimate [Policy Text Block] Schedule H, Line 4i – Schedule of Assets (Held At End of Year) EBP, Schedule of Asset Held for Investment [Text Block] Cover [Abstract] Employer contributions EBP, Change in Net Asset Available for Benefit, Increase from Employer Contribution, Cash Total Investments at Fair Market Value Investments At Fair Value [Member] Investments At Fair Value Minimum Minimum [Member] Interest income on notes receivable from participants EBP, Change in Net Asset Available for Benefit, Increase from Interest Income on Note Receivable from Participant Investment Type [Axis] Investment Type [Axis] Total additions EBP, Change in Net Asset Available for Benefit, Increase from Contribution Fee credits EBP, Change In Net Asset Available For Benefit, Increase From Fee Credits EBP, Change In Net Asset Available For Benefit, Increase From Fee Credits Net appreciation in fair value of investments EBP, Change in Net Asset Available for Benefit, Increase (Decrease) from Gain (Loss) on Investment Interest and dividends EBP, Change in Net Asset Available for Benefit, Increase from Interest and Dividend Income on Investment EBP, Description of Plan [Line Items] EBP, Description of Plan [Line Items] Plan number EBP, Plan Number EBP, Investment, Fair Value and NAV [Line Items] EBP, Investment, Fair Value and NAV [Line Items] Description of Plan EBP, Description of Plan [Text Block] EBP, Statement of Change in Net Asset Available for Benefit [Line Items] EBP, Statement of Change in Net Asset Available for Benefit [Line Items] EBP, Statement of Net Asset Available for Benefit [Table] EBP, Statement of Net Asset Available for Benefit [Table] EBP, Schedule of Asset Held for Investment [Line Items] EBP, Schedule of Asset Held for Investment [Line Items] Contributions EBP, Contribution [Policy Text Block] EBP, Schedule of Asset Held for Investment [Abstract] EBP, Accounting Policy [Table] EBP, Accounting Policy [Table] Allowance for credit losses on notes receivable from participants EBP, Note Receivable from Participant, Allowance for Credit Loss Investment activities: EBP, Change in Net Asset Available for Benefit, Increase (Decrease) from Income (Loss) on Investment [Abstract] Investment, Identifier [Axis] Investment, Identifier [Axis] Cash out limit EBP, Involuntary Cash-out Limit EBP, Involuntary Cash-out Limit Risks and uncertainties EBP, Risk and Uncertainty [Policy Text Block] Funds in transit EBP, Funds In Transit EBP, Funds In Transit Document Information [Line Items] Document Information [Line Items] Change in net assets available for benefits attributed to: EBP, Change in Net Asset Available for Benefit, Increase (Decrease) [Abstract] Maximum percentage of compensation matched EBP, Employer Contribution, Participant Compensation Matched, Percentage EBP, Statement of Change in Net Asset Available for Benefit [Abstract] Level 2 Fair Value, Inputs, Level 2 [Member] Subsequent Event Type [Axis] Subsequent Event Type [Axis] EBP, Tax Status [Table] EBP, Tax Status [Table] Change in net assets available for benefits during the year EBP, Change in Net Asset Available for Benefit, Increase (Decrease) Loan distribution/Deemed distribution of participant loans EBP, Change In Net Asset Available For Benefit, Decrease From Payment To Participant Loans EBP, Change In Net Asset Available For Benefit, Decrease From Payment To Participant Loans Related Party and Party in Interest Transactions EBP, Related Party and Party-in-Interest Transactions [Text Block] EBP, Related Party and Party-in-Interest Transactions [Abstract] EBP, Accounting Policy, Accounting Standard Update, and Change in Accounting Principle [Abstract] Employer contributions receivable EBP, Employer Contribution, Receivable Automatic enrollment percentage of contributions EBP, Participant Contribution, Automatic, Deferral Rate Investments, at fair value: EBP, Investment, Fair Value [Abstract] Distributions to participants or beneficiaries EBP, Change in Net Asset Available for Benefit, Decrease from Payment to Participant Total Investments EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Current Value Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] EBP, Statement of Net Asset Available for Benefit [Abstract] EBP, Accounting Policy [Line Items] EBP, Accounting Policy [Line Items] EBP, Tax Status [Abstract] Fees and expenses EBP, Change In Net Asset Available For Benefit, Decrease From Fee And Expenses EBP, Change In Net Asset Available For Benefit, Decrease From Fee And Expenses Granite Common Stock Fund EBP, Employer, Common Stock Fund [Member] Uninvested cash EBP, Noninterest-Bearing Cash Participant Loans EBP, Asset Held for Investment, Participant Loan, after Deemed Distribution Investment valuation and income recognition EBP, Investment [Policy Text Block] EBP, Participant Contribution, Receivable EBP, Participant Contribution, Receivable Total Fair Value, Inputs, Level 1, Level 2, and Level 3 [Member] Maximum combined pre-tax and after-tax Roth contribution EBP, Participant Contribution, Before Tax And After Tax Roth Contribution, Maximum EBP, Participant Contribution, Before Tax And After Tax Roth Contribution, Maximum Document Type Document Type Plan Termination EBP, Plan Termination [Text Block] Entity Central Index Key Entity Central Index Key Interest rates on notes receivable from participants EBP, Asset Held for Investment, Participant Loan, Interest Rate Common/collective trusts Common Collective Trust [Member] EBP, Tax Status [Line Items] EBP, Tax Status [Line Items] EBP, Subsequent Event [Table] EBP, Subsequent Event [Table] Deductions: EBP, Change in Net Asset Available for Benefit, Decrease [Abstract] Notes receivable from participants EBP, Note Receivable from Participant EBP, Plan Termination [Line Items] EBP, Plan Termination [Line Items] EBP, Plan Termination [Line Items] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Summary of Significant Accounting Policies EBP, Summary of Accounting Policy [Text Block] Entity Registrant Name Entity Registrant Name EBP, Plan Termination [Abstract] EBP, Plan Termination [Abstract] Purchased value EBP, Investment Acquired, Excluding Plan Interest in Master Trust, Cost EBP, Subsequent Event [Abstract] Subsequent Events EBP, Subsequent Event [Text Block] Tax Status EBP, Tax Status [Text Block] Percentage of maximum borrowing to total account EBP, Note Receivable from Participant, Account, Maximum Borrowing, to Total Account, Percentage EBP, Subsequent Event [Line Items] EBP, Subsequent Event [Line Items] Document Information [Table] Document Information [Table] Maximum term for principal residence (in years) EBP, Note Receivable From Participant, Account, Primary Residence, Maximum Borrowing Term EBP, Note Receivable From Participant, Account, Primary Residence, Maximum Borrowing Term Notes Receivable from Participants EBP, Note Receivable from Participant [Policy Text Block] Net gain from investment activities EBP, Change in Net Asset Available for Benefit, Increase (Decrease) from Income (Loss) on Investment EBP, Related Party and Party-in-Interest Transactions [Line Items] EBP, Related Party and Party-in-Interest Transactions [Line Items] Level 3 Fair Value, Inputs, Level 3 [Member] Net assets available for benefits Net assets available for benefits, beginning of year Net assets available for benefits, end of year EBP, Net Asset Available for Benefit Entity [Domain] Entity [Domain] Forfeiture amounts EBP, Forfeited Nonvested Account Percentage of participant matching contributions EBP, Employer Contribution, Matching Percentage Investments measured at NAV practical expedient Fair Value Measured at Net Asset Value Per Share [Member] EBP, Investment, Fair Value and NAV [Table] EBP, Investment, Fair Value and NAV [Table] EBP, Statement of Net Asset Available for Benefit [Line Items] EBP, Statement of Net Asset Available for Benefit [Line Items]