Significant Accounting Policies - Additional Information (Detail) (USD $)	1 Months Ended			12 Months Ended
	Dec. 31, 2014 Derivative	Dec. 31, 2013 Derivative	Dec. 31, 2012	Dec. 31, 2014 Derivative	Dec. 31, 2013 Derivative	Dec. 31, 2012
Significant Accounting Policies [Line Items]
Short-term restricted cash	$ 0	$ 171,000		$ 0	$ 171,000
Long-term restricted cash	312,000	370,000		312,000	370,000
Guarantee related to credit card	50,000			50,000
Property and equipment, depreciation methods				Depreciation is calculated using the straight-line method over the estimated useful lives of the assets
Impairment losses				0	0	0
Non-cash compensation expenses				4,664,000	1,788,000	848,000
Percentage of tax benefit settlement				50.00%
Derivative instruments	0	0		0	0
Defined contribution plan, maximum annual contributions per employee percentage						11,500
Defined contribution plan, maximum contributions per employee per month, percentage				8.33%
Expenses related to severance pay	2,651,000	1,739,000	1,250,000
Other [Member]
Significant Accounting Policies [Line Items]
Defined benefit plan, average payroll percentage per quarter				20.00%
Defined benefit plan, average annual payroll percentage				33.30%
Foreign Exchange Forward Contract Derivatives [Member]
Significant Accounting Policies [Line Items]
Loss on derivative instruments				864,000
Employees and Consultants [Member]
Significant Accounting Policies [Line Items]
Non-cash compensation expenses				$ 4,664,000	$ 1,788,000	$ 848,000
U.S. Plan [Member]
Significant Accounting Policies [Line Items]
Defined contribution plan, employer matching contribution percent of match					100.00%
Defined contribution plan, employer matching contribution percent of participant					50.00%
Defined contribution plan employer contribution, description				VSI matches 100% of each participant's contributions up to a maximum of 3% of the participant's base pay and 50% of each participant's contributions on contributions between 3% and 5% of the participant's base pay.
Defined contribution plan starting date				Jan. 01, 2013
Maximum [Member]
Significant Accounting Policies [Line Items]
Short-term bank deposit, maturity period				1 year
Defined contribution plan, employer matching contribution percentage						3.00%
Maximum [Member] | U.S. Dollars [Member]
Significant Accounting Policies [Line Items]
Interest rate on short-term deposits				0.70%	0.60%
Maximum [Member] | New Israeli Shekels [Member]
Significant Accounting Policies [Line Items]
Interest rate on short-term deposits				0.39%	1.65%
Maximum [Member] | U.S. Plan [Member]
Significant Accounting Policies [Line Items]
Defined contribution plan, employer matching contribution percent of base pay					3.00%
Defined contribution plan, employer matching contribution percent					5.00%
Participant matching contribution percentage of base remuneration					80.00%
Minimum [Member]
Significant Accounting Policies [Line Items]
Short-term bank deposit, maturity period				3 months
Minimum [Member] | U.S. Dollars [Member]
Significant Accounting Policies [Line Items]
Interest rate on short-term deposits				0.30%	0.05%
Minimum [Member] | New Israeli Shekels [Member]
Significant Accounting Policies [Line Items]
Interest rate on short-term deposits				0.35%	0.83%
Minimum [Member] | U.S. Plan [Member]
Significant Accounting Policies [Line Items]
Defined contribution plan, employer matching contribution percent					3.00%