Income Taxes (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2013 Federal tax	Sep. 30, 2013 State tax
Income Tax Examination [Line Items]
SVBOneTimePriorPeriodTaxAdjustment	$ 2.9
Tax years open to examination		Our U.S. federal tax returns for 2010 and subsequent years remain open to examination	Our California tax returns for 2008 and subsequent tax years remain open to examination. Massachusetts tax returns for 2008, 2010 and subsequent years remain open to examination
Unrecognized tax benefit	0.5
Reduction in income tax expense resulting from recognition of unrecognized tax benefit	$ 0.3