Percentage points added to the reference rate to compute the variable rate on the debt instrument.

No definition available.

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Definition

Amount of the required periodic payments applied to principal.

+ References

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- Definition

The fee, expressed as a percentage of the line of credit facility, for the line of credit facility regardless of whether the facility has been used.

+ References

No definition available.

+ Details

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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

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Period Type:	instant

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

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- Definition

The fee, expressed as a percentage of the line of credit facility, for available but unused credit capacity under the credit facility.

+ References

No definition available.

+ Details

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- Definition

Amount of cash inflow from contractual arrangement with the lender, including but not limited to, letter of credit, standby letter of credit and revolving credit arrangements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
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-Name Accounting Standards Codification
-Topic 235
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-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(f))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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- Definition

The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

+ References

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- Definition

Including the current and noncurrent portions, carrying value as of the balance sheet date of uncollateralized debt obligations (with maturities initially due after one year or beyond the operating cycle if longer).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
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-URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910

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Balance Type:	credit
Period Type:	instant

- Definition

The amount committed to pay.

+ References

No definition available.

+ Details

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Namespace Prefix:	wldn_
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Balance Type:	credit
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- Definition

The percentage of debt should be amortized annually.

+ References

No definition available.

+ Details

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- Definition

Represents the percentage of composite interest rate of debt instrument.

+ References

No definition available.

+ Details

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Balance Type:	na
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- Definition

Represents the amount of interest and principal made in conjunction with loans payable.

+ References

No definition available.

+ Details

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- Definition

The contingent increase above the maximum borrowing capacity under the credit facility, if any one or more of the existing banks or new banks agree to provide such increased commitment amount.

+ References

No definition available.

+ Details

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- Definition

Amount represents the line of credit facility minimum borrowing under each tranche.

+ References

No definition available.

+ Details

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Balance Type:	credit
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- Definition

The number of borrowings that the company may make.

+ References

No definition available.

+ Details

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Balance Type:	na
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- Definition

The amount software costs incurred during the period.

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No definition available.

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Balance Type:	debit
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DEBT OBLIGATIONS - Line of credit (Details)					3 Months Ended		12 Months Ended
DEBT OBLIGATIONS - Line of credit (Details)	Jun. 26, 2019 USD ($) item	Nov. 09, 2018 USD ($)	Oct. 01, 2018 USD ($)	Jan. 20, 2017 USD ($)	Sep. 27, 2019 USD ($)	Dec. 28, 2018 USD ($)	Dec. 27, 2019 USD ($)	Dec. 28, 2018 USD ($)	Dec. 29, 2017 USD ($)	Dec. 20, 2018 USD ($)	Oct. 10, 2018 USD ($)
Debt Instrument [Line Items]
Borrowings under term loan facility and line of credit							$ 138,000,000	$ 70,000,000	$ 1,000,000
Composite interest rate							3.70%
Interest rate (as a percent)						4.30%		4.30%
Interest and principal payments						$ 149,881
Unsecured notes payable						$ 1,500,000		$ 1,500,000
Letter of credit issued							$ 2,700,000
Quarterly installments					$ 2,500,000
Utility Customer Agreement
Debt Instrument [Line Items]
Interest rate (as a percent)										4.332%
Unsecured notes payable							900,000
Amount committed to repay										$ 1,700,000
2019 Credit Agreement [Member] \| BMO \| Base rate \| Federal Funds Effective Swap Rate
Debt Instrument [Line Items]
Spread on floating interest rate (as a percent)	0.50%
2019 Credit Agreement [Member] \| BMO \| Base rate \| LIBOR \| Maximum
Debt Instrument [Line Items]
Spread on floating interest rate (as a percent)	1.00%
2019 Credit Agreement [Member] \| BMO \| Base rate \| LIBOR \| Minimum
Debt Instrument [Line Items]
Spread on floating interest rate (as a percent)	0.125%
2019 Credit Agreement [Member] \| BMO \| LIBOR \| Base rate
Debt Instrument [Line Items]
Spread on floating interest rate (as a percent)	1.00%
2019 Credit Agreement [Member] \| BMO \| LIBOR \| Base rate \| Maximum
Debt Instrument [Line Items]
Spread on floating interest rate (as a percent)	2.00%
2019 Credit Agreement [Member] \| BMO \| LIBOR \| Base rate \| Minimum
Debt Instrument [Line Items]
Spread on floating interest rate (as a percent)	1.125%
Term A Loan \| BMO
Debt Instrument [Line Items]
The aggregate amount under the revolving line of credit	$ 100,000,000
Unamortized debt issuance costs							700,000
Delayed Draw Term Loan Facility
Debt Instrument [Line Items]
Maximum borrowing capacity	50,000,000
Line of credit facility minimum borrowing under each tranche	$ 10,000,000
Annual amortization of debt (as a Percent)					2.50%
Delayed Draw Term Loan Facility \| Maximum
Debt Instrument [Line Items]
Number of borrowings \| item	5
Revolving Credit Facility
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 50,000,000
The aggregate amount under the revolving line of credit	$ 100,000,000
Revolving Credit Facility \| BMO \| Maximum
Debt Instrument [Line Items]
Commitment fee (as a percent)	2.00%
Revolving Credit Facility \| BMO \| Minimum
Debt Instrument [Line Items]
Commitment fee (as a percent)	0.84%
Delayed Draw Term Loan And Revolving Credit Facility
Debt Instrument [Line Items]
Unamortized debt issuance costs							800,000
Delayed Draw Term Loan And Revolving Credit Facility \| BMO \| Maximum
Debt Instrument [Line Items]
Fee on unused commitments (as a percent)	0.35%
Delayed Draw Term Loan And Revolving Credit Facility \| BMO \| Minimum
Debt Instrument [Line Items]
Fee on unused commitments (as a percent)	0.15%
2018 Credit Agreement [Member] \| BMO \| Base rate \| Federal Funds Effective Swap Rate
Debt Instrument [Line Items]
Spread on floating interest rate (as a percent)			0.50%
2018 Credit Agreement [Member] \| BMO \| Base rate \| LIBOR \| Maximum
Debt Instrument [Line Items]
Spread on floating interest rate (as a percent)			3.00%
2018 Credit Agreement [Member] \| BMO \| Base rate \| LIBOR \| Minimum
Debt Instrument [Line Items]
Spread on floating interest rate (as a percent)			0.25%
2018 Credit Agreement [Member] \| BMO \| LIBOR \| Base rate
Debt Instrument [Line Items]
Spread on floating interest rate (as a percent)			1.00%
2018 Credit Agreement [Member] \| BMO \| LIBOR \| Base rate \| Maximum
Debt Instrument [Line Items]
Spread on floating interest rate (as a percent)			4.00%
2018 Credit Agreement [Member] \| BMO \| LIBOR \| Base rate \| Minimum
Debt Instrument [Line Items]
Spread on floating interest rate (as a percent)			1.25%
Revolving Credit Facility Member Two
Debt Instrument [Line Items]
Maximum borrowing capacity			$ 30,000,000
Revolving Credit Facility Member Two \| BMO \| Maximum
Debt Instrument [Line Items]
Fee on unused commitments (as a percent)			0.40%
Revolving Credit Facility Member Two \| BMO \| Minimum
Debt Instrument [Line Items]
Fee on unused commitments (as a percent)			0.20%
Delayed Draw Term Loan Facility Two [Member] \| BMO
Debt Instrument [Line Items]
Maximum borrowing capacity			$ 90,000,000
Delayed Draw Term Loan Facility Two [Member] \| BMO \| Maximum
Debt Instrument [Line Items]
Commitment fee (as a percent)			4.00%
Delayed Draw Term Loan Facility Two [Member] \| BMO \| Minimum
Debt Instrument [Line Items]
Commitment fee (as a percent)			0.94%
Term Loan 2018 [Member] \| BMO
Debt Instrument [Line Items]
Maximum borrowing capacity											$ 70,000,000
Borrowings under term loan facility and line of credit		$ 70,000,000
2017 Credit Agreement [Member] \| BMO \| Base rate \| Federal Funds Effective Swap Rate
Debt Instrument [Line Items]
Spread on floating interest rate (as a percent)				0.50%
2017 Credit Agreement [Member] \| BMO \| Base rate \| LIBOR \| Maximum
Debt Instrument [Line Items]
Spread on floating interest rate (as a percent)				1.00%
2017 Credit Agreement [Member] \| BMO \| Base rate \| LIBOR \| Minimum
Debt Instrument [Line Items]
Spread on floating interest rate (as a percent)				0.25%
2017 Credit Agreement [Member] \| BMO \| LIBOR \| Base rate
Debt Instrument [Line Items]
Spread on floating interest rate (as a percent)				1.00%
2017 Credit Agreement [Member] \| BMO \| LIBOR \| Base rate \| Maximum
Debt Instrument [Line Items]
Spread on floating interest rate (as a percent)				2.00%
2017 Credit Agreement [Member] \| BMO \| LIBOR \| Base rate \| Minimum
Debt Instrument [Line Items]
Spread on floating interest rate (as a percent)				1.25%
Revolving line of credit \| BMO
Debt Instrument [Line Items]
Maximum borrowing capacity				$ 35,000,000
Revolving line of credit \| BMO \| Maximum
Debt Instrument [Line Items]
Fee on unused commitments (as a percent)				0.35%
Revolving line of credit \| BMO \| Minimum
Debt Instrument [Line Items]
Fee on unused commitments (as a percent)				0.20%
Standby letter of credit sub-facility \| BMO
Debt Instrument [Line Items]
Maximum borrowing capacity				$ 10,000,000
Standby letter of credit sub-facility \| BMO \| Maximum
Debt Instrument [Line Items]
Commitment fee (as a percent)				1.50%
Standby letter of credit sub-facility \| BMO \| Minimum
Debt Instrument [Line Items]
Commitment fee (as a percent)				0.94%
Notes payable for IBM
Debt Instrument [Line Items]
Interest rate (as a percent)						4.656%		4.656%
Interest and principal payments								$ 6,315
Notes payable for IBM \| Software Agreements
Debt Instrument [Line Items]
Software cost								200,000
Unsecured notes payable						$ 211,000	$ 133,000	$ 211,000