Name:	tris_FeeIncomeOnEarlyMembershipTermination
Namespace Prefix:	tris_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Average percent of revenue from the member distribution system during the period.

No definition available.

Name:	tris_MemberDistributionSystemAveragePercentOfRevenue
Namespace Prefix:	tris_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

The cash inflow associated with the early termination of membership, net of the retirement of related patronage capital.

No definition available.

Name:	tris_ProceedsFromEarlyTerminationOfMembershipNetOfRetirementOfPatronageCapital
Namespace Prefix:	tris_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

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.

No definition available.

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

Amount of deferred revenue as of balance sheet date. Deferred revenue represents collections of cash or other assets related to a revenue producing activity for which revenue has not yet been recognized. Generally, an entity records deferred revenue when it receives consideration from a customer before achieving certain criteria that must be met for revenue to be recognized in conformity with GAAP.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 605
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 13.A.4(a).Q1 Response)
-URI http://asc.fasb.org/extlink&oid=27012821&loc=d3e214044-122780

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Staff Accounting Bulletin (SAB)
-Number Topic 13
-Section A

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

Amount of earnings distributed to patrons of the agricultural cooperative.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 905
-SubTopic 605
-Section 45
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=51665386&loc=d3e6825-110074