Fair Value of Financial Instruments, Carrying Amounts and Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Financial assets [Abstract]
Cash and cash equivalents	$ 1,193,339	$ 1,107,099
Securities available for sale	434,552	439,071
Held to maturity securities	11,646	14,988
Net loans	4,419,921	4,287,585
Accrued interest receivable	9,358	10,031
Financial liabilities [Abstract]
Demand deposits	790,663	652,756
Interest bearing deposits	4,449,708	4,386,439
Short-term borrowings	230,770	214,755
Accrued interest payable	225	474
Level 1 [Member]
Financial assets [Abstract]
Cash and cash equivalents	1,193,339	1,107,099
Securities available for sale	0	0
Held to maturity securities	0	0
Net loans	0	0
Accrued interest receivable	37	39
Financial liabilities [Abstract]
Demand deposits	790,663	652,756
Interest bearing deposits	3,325,774	3,088,064
Short-term borrowings	0	0
Accrued interest payable	30	68
Level 2 [Member]
Financial assets [Abstract]
Cash and cash equivalents	0	0
Securities available for sale	434,552	439,071
Held to maturity securities	11,646	14,988
Net loans	0	0
Accrued interest receivable	1,042	1,458
Financial liabilities [Abstract]
Demand deposits	0	0
Interest bearing deposits	1,123,934	1,298,375
Short-term borrowings	230,770	214,755
Accrued interest payable	195	406
Level 3 [Member]
Financial assets [Abstract]
Cash and cash equivalents	0	0
Securities available for sale	0	0
Held to maturity securities	0	0
Net loans	4,419,921	4,287,585
Accrued interest receivable	8,279	8,534
Financial liabilities [Abstract]
Demand deposits	0	0
Interest bearing deposits	0	0
Short-term borrowings	0	0
Accrued interest payable	0	0
Carrying Value [Member]
Financial assets [Abstract]
Cash and cash equivalents	1,193,339	1,107,099
Securities available for sale	434,552	439,071
Held to maturity securities	10,701	13,824
Federal Reserve Bank and Federal Home Loan Bank stock	5,604	5,506
Net loans	4,349,379	4,194,875
Accrued interest receivable	9,358	10,031
Financial liabilities [Abstract]
Demand deposits	790,663	652,756
Interest bearing deposits	4,450,355	4,384,437
Short-term borrowings	230,770	214,755
Accrued interest payable	$ 225	$ 474

Fair value of investment in debt security measured at amortized cost (held-to-maturity).

No definition available.

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Namespace Prefix:	trst_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents the amount of money in accounts that may bear interest and that the depositor is entitled to withdraw at any time without prior notice.

+ References

No definition available.

+ Details

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Namespace Prefix:	trst_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure. This item represents the aggregate of all interest bearing deposits, saving deposits, negotiable orders of withdrawal (NOW) and time deposits among others.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
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- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents amount as of the balance sheet date of [accrued] interest payable on all forms of debt, including deposits and borrowings, that has been incurred and is unpaid.

+ References

No definition available.

+ Details

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- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents amount as of the balance sheet date of [accrued] interest receivable on loans, investment securities and federal funds sold and other short-term investments that has been earned and is unpaid.

+ References

No definition available.

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- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents the amount shown on an entity's books for investments in Federal Reserve Bank and Federal Home Loan Bank stock.

+ References

No definition available.

+ Details

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- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(6))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=124260329&loc=d3e26610-111562

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-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27161-111563

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- Definition

Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 4
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-Section S99
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-Subparagraph (SX 210.5-02.1)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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Balance Type:	debit
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- References

No definition available.

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- References

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- Definition

Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-URI http://asc.fasb.org/subtopic&trid=2196772

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Period Type:	instant

- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents the amount of short-term debt existing as of the balance sheet date.

+ References

No definition available.

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