SUBSEQUENT EVENTS (Details) - Subsequent Event - Notes Payable to Banks	Apr. 28, 2023
Credit Agreement 2019
Subsequent Events
Debt instrument, covenants, total leverage ratio, maximum permitted to maintain	3.25
Debt instrument, covenants, minimum fixed charge coverage ratio	1.20
Credit Agreement 2019 \| Minimum
Subsequent Events
Commitment fee (as a percent)	0.15%
Credit Agreement 2019 \| Maximum
Subsequent Events
Commitment fee (as a percent)	0.40%
Credit Agreement 2019 \| Base Rate \| Minimum
Subsequent Events
Spread on floating interest rate (as a percent)	0.125%
Credit Agreement 2019 \| Base Rate \| Maximum
Subsequent Events
Spread on floating interest rate (as a percent)	1.25%
Credit Agreement 2019 \| Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate \| Minimum
Subsequent Events
Spread on floating interest rate (as a percent)	1.125%
Interest rate (as a percent)	0.00%
Credit Agreement 2019 \| Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate \| Maximum
Subsequent Events
Spread on floating interest rate (as a percent)	2.25%
Letter of Credit \| Minimum
Subsequent Events
Commitment fee (as a percent)	0.84%
Letter of Credit \| Maximum
Subsequent Events
Commitment fee (as a percent)	1.688%

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

No definition available.

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1B
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- 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

Name:	us-gaap_LineOfCreditFacilityCommitmentFeePercentage
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

No definition available.

+ Details

Name:	us-gaap_SubsequentEventLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The minimum fixed charge coverage ratio (measured as the sum of EBITDA plus rent expense less unfinanced capital expenditures divided by the sum of rent expense plus principal payments plus cash taxes plus cash interest plus restricted payments plus distributions) as a covenant under the credit agreement.

+ References

No definition available.

+ Details

Name:	wldn_DebtInstrumentCovenantsMinimumFixedChargeCoverageRatio
Namespace Prefix:	wldn_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

Debt Instrument, Covenants, Total Leverage Ratio, Maximum Permitted to Maintain

+ References

No definition available.

+ Details

Name:	wldn_DebtInstrumentCovenantsTotalLeverageRatioMaximumPermittedToMaintain
Namespace Prefix:	wldn_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_NotesPayableToBanksMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=wldn_CreditAgreement2019Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_BaseRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=us-gaap_LetterOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: