SEGMENT INFORMATION - By industry segment (Details) - USD ($) $ in Thousands	12 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2017
Operations and identifiable assets by industry segment
Total revenues	$ 1,182,115	$ 1,089,286	$ 960,951
Income (loss) from operations	107,774	55,908	33,292
Segments assets	1,264,864	1,255,691	1,230,087
Capital expenditures	27,412	43,198	17,096
Depreciation and amortization	56,234	69,754	68,235
Security Division
Operations and identifiable assets by industry segment
Total revenues	747,550	690,001	555,197
Capital expenditures	15,830	14,479	10,436
Depreciation and amortization	39,788	55,630	53,924
Healthcare Division
Operations and identifiable assets by industry segment
Total revenues	188,477	189,387	200,034
Capital expenditures	1,372	1,540	1,797
Depreciation and amortization	5,426	4,910	6,495
Optoelectronics and Manufacturing Division
Operations and identifiable assets by industry segment
Total revenues	246,088	209,898	205,720
Capital expenditures	4,760	3,286	2,856
Depreciation and amortization	9,269	7,766	6,561
Corporate
Operations and identifiable assets by industry segment
Income (loss) from operations	(30,598)	(35,030)	(29,359)
Segments assets	79,498	66,453	64,959
Capital expenditures	5,450	23,893	2,007
Depreciation and amortization	1,751	1,448	1,255
Operating Segments \| Security Division
Operations and identifiable assets by industry segment
Total revenues	747,550	690,001	555,197
Income (loss) from operations	97,426	84,106	35,256
Segments assets	793,810	804,527	785,230
Operating Segments \| Healthcare Division
Operations and identifiable assets by industry segment
Total revenues	188,477	189,387	200,034
Income (loss) from operations	12,277	(14,609)	2,624
Segments assets	157,639	167,611	186,021
Operating Segments \| Optoelectronics and Manufacturing Division
Operations and identifiable assets by industry segment
Total revenues	288,630	254,485	236,100
Income (loss) from operations	29,519	22,024	23,792
Segments assets	237,851	220,373	196,567
Eliminations
Operations and identifiable assets by industry segment
Total revenues	(42,542)	(44,587)	(30,380)
Income (loss) from operations	(850)	(583)	979
Segments assets	(3,934)	(3,273)	(2,690)
Eliminations \| Optoelectronics and Manufacturing Division
Operations and identifiable assets by industry segment
Total revenues	$ 42,542	$ 44,587	$ 30,380

Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(11))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-URI http://asc.fasb.org/extlink&oid=115929826&loc=d3e8736-108599

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(12))
-URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910

+ Details

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

- Definition

The aggregate expense recognized in the current period that allocates the cost of tangible assets, intangible assets, or depleting assets to periods that benefit from use of the assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=115929826&loc=d3e8736-108599

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585

+ Details

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

- Definition

The net result for the period of deducting operating expenses from operating revenues.

+ References

No definition available.

+ Details

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

- Definition

The cash outflow associated with the acquisition of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale; includes cash outflows to pay for construction of self-constructed assets.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3213-108585

+ Details

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

- Definition

Amount, including tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value-added and excise.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130545-203045

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130543-203045

+ Details

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

- 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

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

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=osis_SecurityDivisionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=osis_HealthcareDivisionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=osis_OptoelectronicsAndManufacturingDivisionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=us-gaap_CorporateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ConsolidationItemsAxis=us-gaap_OperatingSegmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ConsolidationItemsAxis=us-gaap_IntersegmentEliminationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: