Employee Retirement Benefits - Summary of multi-employer pension plan (Details) - USD ($)	12 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2018
Employee Retirement Benefits
Contributions by the Company	$ 245,824	$ 236,256	$ 269,928
Expiration Date of CBA	May 31, 2021
Surcharge Imposed		No

No definition available.

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- Definition

Expiration date of collective-bargaining arrangement (CBA) requiring contribution to multiemployer pension plan determined to be individually insignificant, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 80
-Section 50
-Paragraph 5
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450657-114947

+ Details

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- Definition

Amount of contribution received by multiemployer pension plan from all employers participating in multiemployer pension plan determined to be individually insignificant.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 80
-Section 50
-Paragraph 7
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450678-114947

+ Details

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Balance Type:	debit
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- Definition

Indicates whether employer paid surcharge to multiemployer pension plan determined to be individually significant. Acceptable values are "No", "Yes" and "NA".

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 80
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=35742348&loc=SL14450788-114948

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 80
-Section 50
-Paragraph 5
-Subparagraph (f)(2)
-URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450657-114947

+ Details

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Data Type:	us-types:surchargeItemType
Balance Type:	na
Period Type:	duration