Change in fair value of loans payable and other adjustments.

No definition available.

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Namespace Prefix:	tern_
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Period Type:	duration

- Definition

Issuance of loans payable for conversion settlement.

+ References

No definition available.

+ Details

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Period Type:	duration

- Definition

Issuance of repurchase payable.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
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Period Type:	duration

- Definition

The amount of the original debt being converted in a noncash (or part noncash) transaction. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=121583591&loc=d3e4304-108586

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=121583591&loc=d3e4332-108586

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=121572278&loc=d3e13433-108611

+ Details

Name:	us-gaap_DebtInstrumentFairValue
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The cash inflow during the period from additional borrowings in aggregate debt. Includes proceeds from short-term and long-term debt.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3255-108585

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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

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Period Type:	duration

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- Details

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Data Type:	na
Balance Type:
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- Details

Name:	us-gaap_DebtInstrumentAxis=tern_TwoThousandAndTwentyNotesAndBridgeLoanMember
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Data Type:	na
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- Details

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- Details

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- Details

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Loans Payable - Schedule of Loans Payable Reported at Fair Value and Measured on Recurring Basis (Details) - USD ($) $ in Thousands	1 Months Ended		12 Months Ended
	Mar. 31, 2021	May 31, 2020	Dec. 31, 2020
Short Term Debt [Line Items]
Balance	$ 0
2020 Notes
Short Term Debt [Line Items]
Issuance of 2020 Notes and Bridge Loan		$ 15,000
Conversion of 2020 convertible promissory notes to Series C convertible preferred stock		$ (15,900)
Recurring \| Loans Payable
Short Term Debt [Line Items]
Balance			$ 0
Change in fair value of loans payable and other adjustments			3,053
Balance			12,880
Recurring \| Loans Payable \| 2020 Notes and Bridge Loan
Short Term Debt [Line Items]
Issuance of 2020 Notes and Bridge Loan			16,800
Recurring \| Loans Payable \| Lilly Asia Ventures Option Exercise
Short Term Debt [Line Items]
Issuance of repurchase payable for the Lilly Asia Ventures option exercise			10,771
Recurring \| Loans Payable \| Bridge Loan
Short Term Debt [Line Items]
Issuance of loans payable for conversion settlement of the Bridge Loan			2,109
Recurring \| Loans Payable \| Series C convertible preferred stock \| Bridge Loan
Short Term Debt [Line Items]
Conversion of 2020 convertible promissory notes to Series C convertible preferred stock			(2,163)
Recurring \| Loans Payable \| Series C convertible preferred stock \| 2020 Notes
Short Term Debt [Line Items]
Conversion of 2020 convertible promissory notes to Series C convertible preferred stock			$ (17,690)