Debt instrument final exit fee accrued.

No definition available.

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Namespace Prefix:	reta_
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Balance Type:	credit
Period Type:	instant

- Definition

Debt instrument final exit fee payment percentage of principal outstanding.

+ References

No definition available.

+ Details

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Period Type:	duration

- Definition

Debt instrument interest only payment period.

+ References

No definition available.

+ Details

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- Definition

Debt instrument interest rate effective percentage excluding debt issuance costs and final exit fee.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	instant

- Definition

Debt instrument interest rate effective percentage including debt issuance costs and final exit fee.

+ References

No definition available.

+ Details

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Namespace Prefix:	reta_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Debt instrument, possible borrowing date.

+ References

No definition available.

+ Details

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Namespace Prefix:	reta_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt instrument prepayment fee percentage.

+ References

No definition available.

+ Details

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Namespace Prefix:	reta_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt instrument, prepayment terms.

+ References

No definition available.

+ Details

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

- Definition

Period to borrow funds after achievement of milestone.

+ References

No definition available.

+ Details

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Namespace Prefix:	reta_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6031897-161870

Reference 2: 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(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 4: 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(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Description of the interest rate as being fixed or variable, and, if variable, identification of the index or rate on which the interest rate is based and the number of points or percentage added to that index or rate to set the rate, and other pertinent information, such as frequency of rate resets.

+ References

+ Details

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

- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(2))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258

+ Details

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

- Definition

Description of the payment terms of the debt instrument (for example, whether periodic payments include principal and frequency of payments) and discussion about any contingencies associated with the payment.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(3))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823

+ Details

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

- Definition

Amount of unamortized debt discount (premium) and debt issuance costs.

+ References

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of commitment fees for the unused borrowing capacity under the long-term financing arrangement that is available to the entity.

+ References

+ Details

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

- Definition

Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 50
-Section 40
-Paragraph 4
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-Name Accounting Standards Codification
-Topic 470
-SubTopic 50
-Section 40
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-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

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

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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Balance Type:	credit
Period Type:	instant

- Definition

The cash inflow from a debt initially having maturity due after one year or beyond the operating cycle, if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3255-108585

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Balance Type:	debit
Period Type:	duration

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- Details

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Balance Type:
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- Details

Name:	us-gaap_LongtermDebtTypeAxis=reta_RestatedAgreementMember
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Data Type:	na
Balance Type:
Period Type:

- Details

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- Details

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Balance Type:
Period Type:

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Balance Type:
Period Type:

- Details

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- Details

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- Details

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- Details

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Term Loan - Additional Information (Details) - USD ($)		9 Months Ended
Term Loan - Additional Information (Details) - USD ($)	Jun. 14, 2018	Sep. 30, 2018	Sep. 30, 2017	Mar. 31, 2017
Debt Instrument [Line Items]
Proceeds from long-term debt		$ 60,000,000	$ 20,000,000
Loss on extinguishment of debt		1,007,000
Term Loan A
Debt Instrument [Line Items]
Debt instrument, carrying value		$ 80,000,000
Loan And Security Agreement \| Term Loan A
Debt Instrument [Line Items]
Maximum borrowing capacity				$ 20,000,000
Amended and Restated Loan and Security Agreement
Debt Instrument [Line Items]
Loss on extinguishment of debt	$ 1,007,000
Debt instrument, prepayment terms		The Company has the option to prepay all, but not less than all, of the borrowed amounts, provided that the Company will be obligated to pay a prepayment fee equal to (a) the aggregate amount of interest that the Company would have paid through the maturity date if prepayment is made on or before the first anniversary of the applicable funding date of the Term Loan, (b) 4.0% of the outstanding principal balance of the applicable Term Loan if prepayment is made after the first anniversary of the applicable funding date of the Term Loan, (c) 3.0% of the outstanding principal balance of the applicable Term Loan if prepayment is made by the after second anniversary of the applicable funding date of the Term Loan, or (d) 1.5% of the outstanding principal balance of the applicable Term Loan if prepayment is made after the third anniversary of the applicable funding date of the Term Loan.
Amended and Restated Loan and Security Agreement \| Loan Prepayment After First Anniversary
Debt Instrument [Line Items]
Debt instrument prepayment fee percentage		4.00%
Amended and Restated Loan and Security Agreement \| Loan Prepayment After Second Anniversary
Debt Instrument [Line Items]
Debt instrument prepayment fee percentage		3.00%
Amended and Restated Loan and Security Agreement \| Loan Prepayment After Third Anniversary
Debt Instrument [Line Items]
Debt instrument prepayment fee percentage		1.50%
Amended and Restated Loan and Security Agreement \| Term Loans
Debt Instrument [Line Items]
Debt instrument, payment terms		All outstanding Term Loans will mature on June 1, 2023. Under the Term A Loan, the Company will make interest-only payments for 24 months through June 1, 2020; however, if the Company draws the Term B Loan, the Company will make interest-only payments for 36 months through June 1, 2021. The interest-only payment period will be followed by 36 equal monthly payments, or 24 equal monthly payments if the Company draws the Term B Loan, of principal and interest payments.
Debt instrument, maturity date		Jun. 01, 2023
Debt instrument, interest rate terms		The Term Loans will bear interest at a floating per annum rate calculated as 7.79% plus the greater of the 30-day U.S. Dollar LIBOR rate reported in The Wall Street Journal on the last business day of the month that immediately precedes the month in which the interest will accrue or 1.91%, with a minimum rate of 9.7% and maximum rate of 12.29%.
Debt instrument, annual interest rate		7.79%
Debt instrument, basis spread on variable rate		1.91%
Amended and Restated Loan and Security Agreement \| Term Loans \| Minimum
Debt Instrument [Line Items]
Debt instrument, annual interest rate		9.70%
Amended and Restated Loan and Security Agreement \| Term Loans \| Maximum
Debt Instrument [Line Items]
Debt instrument, annual interest rate		12.29%
Amended and Restated Loan and Security Agreement \| Term Loan A
Debt Instrument [Line Items]
Proceeds from long-term debt	60,000,000
Debt instrument, interest only payments period		24 months through June 1, 2020
Debt instrument final exit fee payment percentage		6.50%
Debt instrument, carrying value		$ 80,000,000
Debt instrument, debt issuance costs		$ 1,570,000
Debt instrument, effective interest rate before debt issuance costs and final exit fee		10.80%
Debt instrument, effective interest rate including debt issuance costs and final exit fee		13.40%
Debt instrument, final exit fee accrued		$ 5,200,000
Amended and Restated Loan and Security Agreement \| Term Loan A \| Achievement of One of Two Milestones
Debt Instrument [Line Items]
Maximum borrowing capacity	80,000,000
Amended and Restated Loan and Security Agreement \| Term Loan B
Debt Instrument [Line Items]
Period to borrow funds after achievement of milestone		30 days
Debt instrument, possible borrowing date		Dec. 31, 2019
Payment of unused line fee		$ 450,000
Debt instrument, interest only payments period		36 months through June 1, 2021
Debt instrument final exit fee payment percentage		4.00%
Amended and Restated Loan and Security Agreement \| Term Loan B \| Achievement of One of Two Milestones
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 45,000,000