Capital Stock (Details 1) - 12 months ended Mar. 31, 2015 - $ / shares	Total
Pre-Modification [Member]
Market price per share	$ 12.60
Exercise price per share	$ 20
Risk-free interest rate	0.44%
Expected term (years)	2 years 2 months 1 day
Volatility	75.60%
Dividend rate	0.00%
Fair Value per share	$ 3.73
Post-Modification [Member]
Market price per share	12.60
Exercise price per share	$ 10
Risk-free interest rate	0.62%
Expected term (years)	2 years 7 months 2 days
Volatility	76.60%
Dividend rate	0.00%
Fair Value per share	$ 6.65
PreModification 2 [Member]
Market price per share	8.00
Exercise price per share	$ 23.13
Risk-free interest rate	0.04%
Expected term (years)	2 months 27 days
Volatility	69.70%
Dividend rate	0.00%
Fair Value per share	$ .22
PostModification 2 [Member]
Market price per share	8.00
Exercise price per share	$ 13
Risk-free interest rate	0.31%
Expected term (years)	1 year 2 months 27 days
Volatility	69.80%
Dividend rate	0.00%
Fair Value per share	$ 1.31
PreModification 3 [Member]
Market price per share	10.00
Exercise price per share	$ 31.97
Risk-free interest rate	0.33%
Expected term (years)	1 year 4 months 24 days
Volatility	74.40%
Dividend rate	0.00%
Fair Value per share	$ 1.08
PostModification 3 [Member]
Market price per share	10.00
Exercise price per share	$ 24.68
Risk-free interest rate	0.44%
Expected term (years)	2 years 1 month 6 days
Volatility	75.80%
Dividend rate	0.00%
Fair Value per share	$ 2.29
PreModification4 [Member]
Market price per share	8
Exercise price per share	$ 33.49
Risk-free interest rate	0.51%
Expected term (years)	2 years 22 days
Volatility	73.60%
Dividend rate	0.00%
Fair Value per share	$ .91
PostModification4 [Member]
Market price per share	8
Exercise price per share	$ 10
Risk-free interest rate	0.57%
Expected term (years)	2 years 4 months 2 days
Volatility	74.40%
Dividend rate	0.00%
Fair Value per share	$ 2.85

No definition available.

Name:	VSTA_ShareBasedCompensationArrangementsByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsWeightedAverageGrantDateFairValuePeriodIncreaseDecrease
Namespace Prefix:	VSTA_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

Expected dividends to be paid to holders of the underlying shares or financial instruments (expressed as a percentage of the share or instrument's price).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (e)

-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

+ Details

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

- Definition

Period the instrument, asset or liability is expected to be outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

+ Details

Name:	us-gaap_FairValueAssumptionsExpectedTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Measure of dispersion, in percentage terms (for instance, the standard deviation or variance), for a given stock price.

+ References

+ Details

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

- Definition

Risk-free interest rate assumption used in valuing an instrument.

+ References

+ Details

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

- Definition

Change in the weighted average exercise price of options outstanding.

+ References

No definition available.

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingPeriodIncreaseDecreaseWeightedAverageExercisePrice
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

Weighted average price at which grantees could acquire or could have acquired the underlying shares with respect to any other type of change in shares reserved for issuance.

+ References

No definition available.

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsOtherShareIncreaseDecreaseInPeriodWeightedAverageExercisePrice
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_ShortTermDebtTypeAxis=VSTA_PreModificationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ShortTermDebtTypeAxis=VSTA_PostModificationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ShortTermDebtTypeAxis=VSTA_PreMod2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ShortTermDebtTypeAxis=VSTA_PostMod2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ShortTermDebtTypeAxis=VSTA_PreMod3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ShortTermDebtTypeAxis=VSTA_PostMod3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ShortTermDebtTypeAxis=VSTA_PreModification4Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ShortTermDebtTypeAxis=VSTA_PostModification4Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: