Commitments and Contingencies	6 Months Ended
Jun. 30, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Operating Lease In June 2016, the Company and G&I VII Encino Trace II LP (the “Landlord”) entered into a lease for the Company's corporate headquarters and research facility in Austin, Texas (the “Headquarters”) under an operating lease agreement (the “G&I Lease”). The initial term of the G&I Lease was for a 123-month period, with the option to extend the G&I Lease for up to two consecutive 60-month terms. In November 2016, following the workforce reduction described in Note 10, the Company determined not to occupy and ceased use of the headquarters and research facility under the G&I Lease. See Note 10 to the financial statements for further information on accounting for the G&I Lease. The G&I Lease provides annual base rent of approximately $600,000 in the first year after a three-month rent free period following January 1, 2017, the commencement date of the G&I Lease. with subsequent annual increases of approximately 3% in the annual base rent. In connection with the G&I Lease, the landlord has provided a tenant improvement allowance of approximately $1.9 million to be used by the Company to build-out certain improvements to the Headquarters. There have been no draws on the improvement allowance as of June 30, 2017. In connection with the G&I Lease, Mirna obtained a standby letter of credit (the “Letter of Credit”) for the initial amount of approximately $2.4 million, which the Landlord may draw down in the event of default. In May 2017, the Company and the Landlord entered into a Lease Termination Agreement and Release (the “Lease Settlement”) to terminate the G&I Lease for consideration equal to the Settlement Amount. In June 2017, the termination of the G&I Lease became effective upon entry by the Landlord into an agreement with a third party regarding the premises previously covered under the G&I Lease. The Lease Settlement includes standard representations and warranties and released both the Company and the Landlord from their mutual obligations under the G&I Lease, provided, for purposes of the Landlord's release, the Company does not file for bankruptcy or otherwise make an assignment for the benefit of creditors within 90 days of the Landlord's receipt of the Settlement Amount. In June 2017, the Landlord released the Letter of Credit to the Company and the balance of restricted cash was reclassified to cash and cash equivalents at June 30, 2017. There were no draws on the Letter of Credit at any time during which it was outstanding. CPRIT In August 2010, the Company entered into a grant contract (the “2010 Contract”) with CPRIT, under which the Company received a $10.3 million commercialization award from the State of Texas through CPRIT. CPRIT was established to expedite innovation and commercialization in the area of cancer research and to enhance access to evidence-based prevention programs and services throughout the State of Texas. The award was a three-year award that was funded annually, and the contract terminated on January 31, 2014, subject to the Company's obligations to make certain payments that survive termination. In May 2017, the Company entered into a letter agreement (the “Letter Agreement”) with CPRIT related to the 2010 Contract and the 2014 Contract. In May 2017, Mirna and CPRIT entered into an attachment (the “2010 Amendment”) to amend the 2010 Contract. Pursuant to the Letter Agreement and the 2010 Amendment, in May 2017, Mirna repaid CPRIT $5 million as consideration for the termination of certain grant repayment and other obligations under the 2010 Contract and 2014 Contract. The Company recognized the repayment in research and development expenses within the statement of operations for the three and six month periods ended June 30, 2017.

Commitments and Contingencies

Operating Lease

In June 2016, the Company and G&I VII Encino Trace II LP (the “Landlord”) entered into a lease for the Company's corporate headquarters and research facility in Austin, Texas (the “Headquarters”) under an operating lease agreement (the “G&I Lease”). The initial term of the G&I Lease was for a 123-month period, with the option to extend the G&I Lease for up to two consecutive 60-month terms. In November 2016, following the workforce reduction described in Note 10, the Company determined not to occupy and ceased use of the headquarters and research facility under the G&I Lease. See Note 10 to the financial statements for further information on accounting for the G&I Lease.

The G&I Lease provides annual base rent of approximately $600,000 in the first year after a three-month rent free period following January 1, 2017, the commencement date of the G&I Lease. with subsequent annual increases of approximately 3% in the annual base rent. In connection with the G&I Lease, the landlord has provided a tenant improvement allowance of approximately $1.9 million to be used by the Company to build-out certain improvements to the Headquarters. There have been no draws on the improvement allowance as of June 30, 2017.

In connection with the G&I Lease, Mirna obtained a standby letter of credit (the “Letter of Credit”) for the initial amount of approximately $2.4 million, which the Landlord may draw down in the event of default.

In May 2017, the Company and the Landlord entered into a Lease Termination Agreement and Release (the “Lease Settlement”) to terminate the G&I Lease for consideration equal to the Settlement Amount. In June 2017, the termination of the G&I Lease became effective upon entry by the Landlord into an agreement with a third party regarding the premises previously covered under the G&I Lease. The Lease Settlement includes standard representations and warranties and released both the Company and the Landlord from their mutual obligations under the G&I Lease, provided, for purposes of the Landlord's release, the Company does not file for bankruptcy or otherwise make an assignment for the benefit of creditors within 90 days of the Landlord's receipt of the Settlement Amount.

In June 2017, the Landlord released the Letter of Credit to the Company and the balance of restricted cash was reclassified to cash and cash equivalents at June 30, 2017. There were no draws on the Letter of Credit at any time during which it was outstanding.

CPRIT

In August 2010, the Company entered into a grant contract (the “2010 Contract”) with CPRIT, under which the Company received a $10.3 million commercialization award from the State of Texas through CPRIT. CPRIT was established to expedite innovation and commercialization in the area of cancer research and to enhance access to evidence-based prevention programs and services throughout the State of Texas. The award was a three-year award that was funded annually, and the contract terminated on January 31, 2014, subject to the Company's obligations to make certain payments that survive termination.

In May 2017, the Company entered into a letter agreement (the “Letter Agreement”) with CPRIT related to the 2010 Contract and the 2014 Contract. In May 2017, Mirna and CPRIT entered into an attachment (the “2010 Amendment”) to amend the 2010 Contract. Pursuant to the Letter Agreement and the 2010 Amendment, in May 2017, Mirna repaid CPRIT $5 million as consideration for the termination of certain grant repayment and other obligations under the 2010 Contract and 2014 Contract. The Company recognized the repayment in research and development expenses within the statement of operations for the three and six month periods ended June 30, 2017.