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    <Log type="Info">Columns in Cash Flows statement 'CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)' have maximum duration 365 days and at least 30 values. Shorter duration columns must have at least one fourth (7) as many values. Column '1/1/2013 - 3/31/2013' is shorter (89 days) and has only 2 values, so it is being removed.</Log>
    <Log type="Info">Columns in Cash Flows statement 'CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)' have maximum duration 365 days and at least 30 values. Shorter duration columns must have at least one fourth (7) as many values. Column '4/1/2013 - 6/30/2013' is shorter (90 days) and has only 1 values, so it is being removed.</Log>
    <Log type="Info">Columns in Cash Flows statement 'CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)' have maximum duration 365 days and at least 30 values. Shorter duration columns must have at least one fourth (7) as many values. Column '7/1/2013 - 9/30/2013' is shorter (91 days) and has only 1 values, so it is being removed.</Log>
    <Log type="Info">Columns in Cash Flows statement 'CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)' have maximum duration 365 days and at least 30 values. Shorter duration columns must have at least one fourth (7) as many values. Column '10/1/2013 - 12/31/2013' is shorter (91 days) and has only 2 values, so it is being removed.</Log>
    <Log type="Info">Columns in Cash Flows statement 'CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)' have maximum duration 365 days and at least 30 values. Shorter duration columns must have at least one fourth (7) as many values. Column '1/1/2014 - 3/31/2014' is shorter (89 days) and has only 2 values, so it is being removed.</Log>
    <Log type="Info">Columns in Cash Flows statement 'CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)' have maximum duration 365 days and at least 30 values. Shorter duration columns must have at least one fourth (7) as many values. Column '4/1/2014 - 6/30/2014' is shorter (90 days) and has only 1 values, so it is being removed.</Log>
    <Log type="Info">Columns in Cash Flows statement 'CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)' have maximum duration 365 days and at least 30 values. Shorter duration columns must have at least one fourth (7) as many values. Column '7/1/2014 - 9/30/2014' is shorter (91 days) and has only 1 values, so it is being removed.</Log>
    <Log type="Info">Columns in Cash Flows statement 'CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)' have maximum duration 365 days and at least 30 values. Shorter duration columns must have at least one fourth (7) as many values. Column '10/1/2014 - 12/31/2014' is shorter (91 days) and has only 2 values, so it is being removed.</Log>
    <Log type="Info">'Monetary' elements on report '40101 - Disclosure - Nature of business (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '40301 - Disclosure - Property and equipment (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Shares' elements on report '40601 - Disclosure - Common stock (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '40803 - Disclosure - Income taxes (Details 3)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '40901 - Disclosure - Commitments and contingencies (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Shares' elements on report '41201 - Disclosure - Quarterly Financial Information (unaudited, in thousands, except per share data) (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '41201 - Disclosure - Quarterly Financial Information (unaudited, in thousands, except per share data) (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">Process Flow-Through: 00100 - Statement - CONSOLIDATED BALANCE SHEETS</Log>
    <Log type="Info">	Process Flow-Through: Removing column 'Dec. 31, 2012'</Log>
    <Log type="Info">	Process Flow-Through: Removing column 'Dec. 31, 2011'</Log>
    <Log type="Info">Process Flow-Through: 00105 - Statement - CONSOLIDATED BALANCE SHEETS (Parenthetical)</Log>
    <Log type="Info">Process Flow-Through: 00200 - Statement - CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS</Log>
    <Log type="Info">	Process Flow-Through: Removing column '3 Months Ended
Dec. 31, 2014'</Log>
    <Log type="Info">	Process Flow-Through: Removing column '3 Months Ended
Sep. 30, 2014'</Log>
    <Log type="Info">	Process Flow-Through: Removing column '3 Months Ended
Jun. 30, 2014'</Log>
    <Log type="Info">	Process Flow-Through: Removing column '3 Months Ended
Mar. 31, 2014'</Log>
    <Log type="Info">	Process Flow-Through: Removing column '3 Months Ended
Dec. 31, 2013'</Log>
    <Log type="Info">	Process Flow-Through: Removing column '3 Months Ended
Sep. 30, 2013'</Log>
    <Log type="Info">	Process Flow-Through: Removing column '3 Months Ended
Jun. 30, 2013'</Log>
    <Log type="Info">	Process Flow-Through: Removing column '3 Months Ended
Mar. 31, 2013'</Log>
    <Log type="Info">Process Flow-Through: 00305 - Statement - CONSOLIDATED STATEMENTS OF REDEEMABLE CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' (DEFICIT) EQUITY (Parenthetical)</Log>
    <Log type="Info">Process Flow-Through: 00400 - Statement - CONSOLIDATED STATEMENTS OF CASH FLOWS</Log>
  </Logs>
  <InputFiles>
    <File>vstm-20141231.xml</File>
    <File>vstm-20141231.xsd</File>
    <File>vstm-20141231_cal.xml</File>
    <File>vstm-20141231_def.xml</File>
    <File>vstm-20141231_lab.xml</File>
    <File>vstm-20141231_pre.xml</File>
  </InputFiles>
  <SupplementalFiles />
  <BaseTaxonomies />
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
