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Investment Securities - Summary of Unrealized Losses on Available for Sale Securities (Detail) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2015
Investment
Dec. 31, 2014
Investments, Unrealized Loss Position [Line Items]    
Less than 12 months - Fair Value of Investments $ 813,101us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue [1] $ 3,209,821us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
Less than 12 months - Unrealized Losses (2,018)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss [1] (8,301)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
12 months or longer - Unrealized Losses 428,635us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue [1] 961,186us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
12 months or longer - Unrealized Losses (6,216)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss [1] (19,842)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
Fair Value of Investments 1,241,736us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue [1] 4,171,007us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
Unrealized Losses (8,234)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss [1] (28,143)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
Number of investments in unrealized loss position 51us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions1  
Number of investments with unrealized losses greater than 12 months 17us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsGreaterThanOrEqualToOneYear  
U.S. treasury securities    
Investments, Unrealized Loss Position [Line Items]    
Less than 12 months - Fair Value of Investments 176,467us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember		 2,297,895us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember
Less than 12 months - Unrealized Losses (264)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember		 (4,386)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember
12 months or longer - Unrealized Losses 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember		 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember
12 months or longer - Unrealized Losses 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember		 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember
Fair Value of Investments 176,467us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember		 2,297,895us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember
Unrealized Losses (264)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember		 (4,386)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember
U.S. agency debentures    
Investments, Unrealized Loss Position [Line Items]    
Less than 12 months - Fair Value of Investments 390,034us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember		 249,266us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Less than 12 months - Unrealized Losses (1,214)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember		 (489)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
12 months or longer - Unrealized Losses 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember		 507,385us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
12 months or longer - Unrealized Losses 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember		 (8,488)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Fair Value of Investments 390,034us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember		 756,651us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Unrealized Losses (1,214)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember		 (8,977)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Residential mortgage-backed securities | Agency-issued mortgage-backed securities    
Investments, Unrealized Loss Position [Line Items]    
Less than 12 months - Fair Value of Investments 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
Less than 12 months - Unrealized Losses 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
12 months or longer - Unrealized Losses 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
12 months or longer - Unrealized Losses 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
Fair Value of Investments 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_InvestmentTypeAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
Unrealized Losses 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ us-gaap_InvestmentTypeAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
Residential mortgage-backed securities | Agency-issued collateralized mortgage obligations | Fixed rate    
Investments, Unrealized Loss Position [Line Items]    
Less than 12 months - Fair Value of Investments 244,285us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ sivb_InvestmentHoldingsAxis
= us-gaap_FixedRateResidentialMortgageMember
/ us-gaap_InvestmentTypeAxis
= sivb_AgencyCollateralizedMortgageObligationsMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 662,092us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ sivb_InvestmentHoldingsAxis
= us-gaap_FixedRateResidentialMortgageMember
/ us-gaap_InvestmentTypeAxis
= sivb_AgencyCollateralizedMortgageObligationsMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
Less than 12 months - Unrealized Losses (244)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ sivb_InvestmentHoldingsAxis
= us-gaap_FixedRateResidentialMortgageMember
/ us-gaap_InvestmentTypeAxis
= sivb_AgencyCollateralizedMortgageObligationsMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 (3,104)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ sivb_InvestmentHoldingsAxis
= us-gaap_FixedRateResidentialMortgageMember
/ us-gaap_InvestmentTypeAxis
= sivb_AgencyCollateralizedMortgageObligationsMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
12 months or longer - Unrealized Losses 428,635us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ sivb_InvestmentHoldingsAxis
= us-gaap_FixedRateResidentialMortgageMember
/ us-gaap_InvestmentTypeAxis
= sivb_AgencyCollateralizedMortgageObligationsMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 453,801us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ sivb_InvestmentHoldingsAxis
= us-gaap_FixedRateResidentialMortgageMember
/ us-gaap_InvestmentTypeAxis
= sivb_AgencyCollateralizedMortgageObligationsMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
12 months or longer - Unrealized Losses (6,216)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ sivb_InvestmentHoldingsAxis
= us-gaap_FixedRateResidentialMortgageMember
/ us-gaap_InvestmentTypeAxis
= sivb_AgencyCollateralizedMortgageObligationsMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 (11,354)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ sivb_InvestmentHoldingsAxis
= us-gaap_FixedRateResidentialMortgageMember
/ us-gaap_InvestmentTypeAxis
= sivb_AgencyCollateralizedMortgageObligationsMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
Fair Value of Investments 672,920us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ sivb_InvestmentHoldingsAxis
= us-gaap_FixedRateResidentialMortgageMember
/ us-gaap_InvestmentTypeAxis
= sivb_AgencyCollateralizedMortgageObligationsMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 1,115,893us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ sivb_InvestmentHoldingsAxis
= us-gaap_FixedRateResidentialMortgageMember
/ us-gaap_InvestmentTypeAxis
= sivb_AgencyCollateralizedMortgageObligationsMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
Unrealized Losses (6,460)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ sivb_InvestmentHoldingsAxis
= us-gaap_FixedRateResidentialMortgageMember
/ us-gaap_InvestmentTypeAxis
= sivb_AgencyCollateralizedMortgageObligationsMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 (14,458)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ sivb_InvestmentHoldingsAxis
= us-gaap_FixedRateResidentialMortgageMember
/ us-gaap_InvestmentTypeAxis
= sivb_AgencyCollateralizedMortgageObligationsMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
Residential mortgage-backed securities | Agency-issued collateralized mortgage obligations | Variable rate    
Investments, Unrealized Loss Position [Line Items]    
Less than 12 months - Fair Value of Investments 934us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ sivb_InvestmentHoldingsAxis
= us-gaap_AdjustableRateResidentialMortgageMember
/ us-gaap_InvestmentTypeAxis
= sivb_AgencyCollateralizedMortgageObligationsMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		  
Less than 12 months - Unrealized Losses (3)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ sivb_InvestmentHoldingsAxis
= us-gaap_AdjustableRateResidentialMortgageMember
/ us-gaap_InvestmentTypeAxis
= sivb_AgencyCollateralizedMortgageObligationsMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		  
12 months or longer - Unrealized Losses 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ sivb_InvestmentHoldingsAxis
= us-gaap_AdjustableRateResidentialMortgageMember
/ us-gaap_InvestmentTypeAxis
= sivb_AgencyCollateralizedMortgageObligationsMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		  
12 months or longer - Unrealized Losses 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ sivb_InvestmentHoldingsAxis
= us-gaap_AdjustableRateResidentialMortgageMember
/ us-gaap_InvestmentTypeAxis
= sivb_AgencyCollateralizedMortgageObligationsMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		  
Fair Value of Investments 934us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ sivb_InvestmentHoldingsAxis
= us-gaap_AdjustableRateResidentialMortgageMember
/ us-gaap_InvestmentTypeAxis
= sivb_AgencyCollateralizedMortgageObligationsMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		  
Unrealized Losses (3)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ sivb_InvestmentHoldingsAxis
= us-gaap_AdjustableRateResidentialMortgageMember
/ us-gaap_InvestmentTypeAxis
= sivb_AgencyCollateralizedMortgageObligationsMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		  
Equity securities    
Investments, Unrealized Loss Position [Line Items]    
Less than 12 months - Fair Value of Investments 1,381us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember		 568us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember
Less than 12 months - Unrealized Losses (293)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember		 (322)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember
12 months or longer - Unrealized Losses 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember		 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember
12 months or longer - Unrealized Losses 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember		 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember
Fair Value of Investments 1,381us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember		 568us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember
Unrealized Losses $ (293)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember		 $ (322)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember
[1] As of March 31, 2015, we identified a total of 51 investments that were in unrealized loss positions, of which 17 investments totaling $428.6 million with unrealized losses of $6.2 million have been in an impaired position for a period of time greater than 12 months. As of March 31, 2015, we do not intend to sell any impaired fixed income investment securities prior to recovery of our adjusted cost basis, and it is more likely than not that we will not be required to sell any of our securities prior to recovery of our adjusted cost basis. Based on our analysis as of March 31, 2015, we deem all impairments to be temporary, and therefore changes in value for our temporarily impaired securities as of the same date are included in other comprehensive income. Market valuations and impairment analyses on assets in the available-for-sale securities portfolio are reviewed and monitored on a quarterly basis.