Stock Compensation Plans - Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Vested and Expected to Vest, Outstanding and Exercisable (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Shares outstanding beginning balance	21
Exercise of stock options, Shares	(20)
Expired, Shares	(1)
Shares outstanding ending balance	0	21
Weighted average exercise price beginning balance	$ 2.55
Weighted average exercise price, Exercised	$ 2.55
Weighted average exercise price, Expired	$ 2.53
Weighted average exercise price ending balance		$ 2.55
Weighted average remaining term (Years), beginning balance	18 days
Aggregate intrinsic value beginning balance	$ 109
Aggregate intrinsic value, Exercised	(100)	(1,429)	(3,146)
Aggregate intrinsic value ending balance	$ 0	$ 109

Stock Compensation Plans - Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Vested and Expected to Vest, Outstanding and Exercisable (Detail) (USD $)
In Thousands, except Per Share data, unless otherwise specified

12 Months Ended

Dec. 31, 2014

Dec. 31, 2013

Dec. 31, 2012

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Shares outstanding beginning balance

21vdsi_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfOptionsOutstanding

Exercise of stock options, Shares

(20)us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised

Expired, Shares

(1)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriod

Shares outstanding ending balance

0vdsi_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfOptionsOutstanding

21vdsi_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfOptionsOutstanding

Weighted average exercise price beginning balance

$ 2.55us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice

Weighted average exercise price, Exercised

$ 2.55us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice

Weighted average exercise price, Expired

$ 2.53us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationsInPeriodWeightedAverageExercisePrice

Weighted average exercise price ending balance

$ 2.55us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice

Weighted average remaining term (Years), beginning balance

18 days

Aggregate intrinsic value beginning balance

$ 109us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue

Aggregate intrinsic value, Exercised

(100)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue

(1,429)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue

(3,146)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue

Aggregate intrinsic value ending balance

$ 0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue

$ 109us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (d)(2)

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- Definition

Number of options or other stock instruments for which the right to exercise has lapsed under the terms of the plan agreements.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(1)(iv)(4)

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- Definition

Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

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- Definition

Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(1)(i)

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- Definition

Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (e)(1)

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- Definition

Weighted average price at which option holders acquired shares when converting their stock options into shares.

+ References

No definition available.

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- Definition

Weighted average price at which grantees could have acquired the underlying shares with respect to stock options of the plan that expired.

+ References

No definition available.

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- Definition

Number of share options (or share units) exercised during the current period.

+ References

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

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Share based compensation arrangement by share based payment award number of options outstanding.

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