STOCK OPTIONS AND RESTRICTED SHARES (Summary of Unrecognized Compensation Cost) (Details) $ in Thousands	12 Months Ended
Mar. 31, 2019 USD ($)
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Fiscal 2020	$ 535
Fiscal 2021	239
Fiscal 2022	40
Fiscal 2023	2
Fiscal 2024	0
Thereafter	0
Total compensation cost	$ 816
Remaining weighted average expected term	1 year 8 months 12 days

Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Due in Five Years.

No definition available.

Name:	oesx_EmployeeServiceShareBasedCompensationNonvestedAwardsCompensationCostNotYetRecognizedDueInFiveYears
Namespace Prefix:	oesx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Due in Four Years.

+ References

No definition available.

+ Details

Name:	oesx_EmployeeServiceShareBasedCompensationNonvestedAwardsCompensationCostNotYetRecognizedDueInFourYears
Namespace Prefix:	oesx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Due in Three Years.

+ References

No definition available.

+ Details

Name:	oesx_EmployeeServiceShareBasedCompensationNonvestedAwardsCompensationCostNotYetRecognizedDueInThreeYears
Namespace Prefix:	oesx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Due in Two Years.

+ References

No definition available.

+ Details

Name:	oesx_EmployeeServiceShareBasedCompensationNonvestedAwardsCompensationCostNotYetRecognizedDueInTwoYears
Namespace Prefix:	oesx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Due Thereafter.

+ References

No definition available.

+ Details

Name:	oesx_EmployeeServiceShareBasedCompensationNonvestedAwardsCompensationCostNotYetRecognizedDueThereafter
Namespace Prefix:	oesx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Next Twelve Months.

+ References

No definition available.

+ Details

Name:	oesx_EmployeeServiceShareBasedCompensationNonvestedAwardsCompensationCostNotYetRecognizedNextTwelveMonths
Namespace Prefix:	oesx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- References

No definition available.

+ Details

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

- Definition

Unrecognized cost of unvested share-based compensation awards.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

+ Details

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

- Definition

Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

+ Details

Name:	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration