REVENUE RECOGNITION - Summary of Receivables, Contract Assets, and Contract Liabilities (Details) $ in Thousands	3 Months Ended
Jun. 30, 2025 USD ($)
Receivables
Beginning balance	$ 247,622
Increase/(Decrease)	(39,297)
Ending balance	208,325
Unbilled work in progress, net of allowance for credit losses
Beginning balance	157,760
Increase/(Decrease)	23,058
Ending balance	180,818
Contract Assets
Beginning balance	9,704
Increase/(Decrease)	148
Ending balance	9,852
Contract Liabilities
Beginning balance	48,215
Increase/(Decrease)	3,281
Ending balance	$ 51,496

Change In Unbilled Work In Process [Roll Forward]

No definition available.

Name:	hli_ChangeInUnbilledWorkInProcessRollForward
Namespace Prefix:	hli_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Change in Contract with Customer, Receivables, Net [Roll Forward]

+ References

No definition available.

+ Details

Name:	hli_ChangeinContractwithCustomerReceivablesNetRollForward
Namespace Prefix:	hli_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Changes in Contract with Customer, Asset [Roll Forward]

+ References

No definition available.

+ Details

Name:	hli_ChangesinContractwithCustomerAssetRollForward
Namespace Prefix:	hli_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Changes in Contract with Customer, Liability [Roll Forward]

+ References

No definition available.

+ Details

Name:	hli_ChangesinContractwithCustomerLiabilityRollForward
Namespace Prefix:	hli_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Contract with Customer, Receivables, Net

+ References

No definition available.

+ Details

Name:	hli_ContractwithCustomerReceivablesNet
Namespace Prefix:	hli_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Increase (Decrease) in Contract with Customer, Receivables, Net

+ References

No definition available.

+ Details

Name:	hli_IncreaseDecreaseinContractwithCustomerReceivablesNet
Namespace Prefix:	hli_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Increase (Decrease) in Unbilled Work in Process

+ References

No definition available.

+ Details

Name:	hli_IncreaseDecreaseinUnbilledWorkinProcess
Namespace Prefix:	hli_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Unbilled Receivables, Work In Process

+ References

No definition available.

+ Details

Name:	hli_UnbilledReceivablesWorkInProcess
Namespace Prefix:	hli_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount, after allowance for credit loss, of right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479837/606-10-45-3

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479837/606-10-45-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 8
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479806/606-10-50-8

+ Details

Name:	us-gaap_ContractWithCustomerAssetNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479837/606-10-45-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 8
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479806/606-10-50-8

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479837/606-10-45-2

+ Details

Name:	us-gaap_ContractWithCustomerLiability
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of increase (decrease) in right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 230
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 28
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-28

+ Details

Name:	us-gaap_IncreaseDecreaseInContractWithCustomerAsset
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of increase (decrease) in obligation to transfer good or service to customer for which consideration has been received or is receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 912
-SubTopic 310
-Name Accounting Standards Codification
-Section 45
-Paragraph 11
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478345/912-310-45-11

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 230
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 28
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-28

+ Details

Name:	us-gaap_IncreaseDecreaseInContractWithCustomerLiability
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration