Major Components of Investment Securities Portfolio (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Investment Holdings [Line Items]
Amortized Cost	$ 11,152,150		$ 10,384,741
Unrealized Gains	192,960		157,105
Unrealized Losses	(1,933)		(5,800)
Carrying Value	11,343,177		10,536,046
Non-marketable securities	1,184,265		1,004,440
Investment securities	12,527,442		11,540,486
Fair value accounting | Venture capital and private equity fund investments
Investment Holdings [Line Items]
Non-marketable securities	665,921	[1]	611,824	[1]
Fair value accounting | Other venture capital investments
Investment Holdings [Line Items]
Non-marketable securities	127,091	[2]	124,121	[2]
Fair value accounting | Other investments
Investment Holdings [Line Items]
Non-marketable securities	0		987
Equity method accounting | Other investments
Investment Holdings [Line Items]
Non-marketable securities	139,330	[3]	68,252	[3]
Equity method accounting | Low income housing tax credit funds
Investment Holdings [Line Items]
Non-marketable securities	70,318		34,894
Cost method accounting | Venture capital and private equity fund investments
Investment Holdings [Line Items]
Non-marketable securities	161,884	[4]	145,007	[4]
Cost method accounting | Other investments
Investment Holdings [Line Items]
Non-marketable securities	19,721		19,355
U.S. treasury securities
Investment Holdings [Line Items]
Amortized Cost	25,057		25,233
Unrealized Gains	190		731
Unrealized Losses	0		0
Carrying Value	25,247		25,964
U.S. agency debentures
Investment Holdings [Line Items]
Amortized Cost	3,370,455		2,822,158
Unrealized Gains	77,173		52,864
Unrealized Losses	0		(90)
Carrying Value	3,447,628		2,874,932
Residential mortgage-backed securities | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises
Investment Holdings [Line Items]
Amortized Cost	1,428,682		1,529,466
Unrealized Gains	44,858		34,926
Unrealized Losses	(107)		(106)
Carrying Value	1,473,433		1,564,286
Residential mortgage-backed securities | Agency-issued collateralized mortgage obligations | Fixed rate
Investment Holdings [Line Items]
Amortized Cost	4,063,020		3,317,285
Unrealized Gains	41,949		56,546
Unrealized Losses	(995)		(71)
Carrying Value	4,103,974		3,373,760
Residential mortgage-backed securities | Agency-issued collateralized mortgage obligations | Variable rate
Investment Holdings [Line Items]
Amortized Cost	1,760,551		2,416,158
Unrealized Gains	12,201		1,554
Unrealized Losses	(4)		(4,334)
Carrying Value	1,772,748		2,413,378
Agency-issued commercial mortgage-backed securities
Investment Holdings [Line Items]
Amortized Cost	416,487		176,646
Unrealized Gains	6,100		2,047
Unrealized Losses	(489)		0
Carrying Value	422,098		178,693
Municipal bonds and notes
Investment Holdings [Line Items]
Amortized Cost	85,790		92,241
Unrealized Gains	7,750		8,257
Unrealized Losses	(11)		0
Carrying Value	93,529		100,498
Equity securities
Investment Holdings [Line Items]
Amortized Cost	2,108		5,554
Unrealized Gains	2,739		180
Unrealized Losses	(327)		(1,199)
Carrying Value	$ 4,520		$ 4,535

[1] The following table shows the amounts of venture capital and private equity fund investments held by the following consolidated funds and our ownership percentage of each fund at December 31, 2012 and December 31, 2011 (fair value accounting):

[2] The following table shows the amounts of other venture capital investments held by the following consolidated funds and our ownership percentage of each fund at December 31, 2012 and December 31, 2011 (fair value accounting): December 31, 2012 December 31, 2011(Dollars in thousands) Amount Ownership % Amount Ownership %Silicon Valley BancVentures, LP $43,493 10.7% $17,878 10.7%SVB Capital Partners II, LP (i) 79,761 5.1 61,099 5.1SVB India Capital Partners I, LP (ii) — — 42,832 14.4SVB Capital Shanghai Yangpu Venture Capital Fund 3,837 6.8 2,312 6.8Total other venture capital investments $127,091 $124,121

[3] The following table shows the carrying value and our ownership percentage of each investment at December 31, 2012 and December 31, 2011 (equity method accounting): December 31, 2012 December 31, 2011(Dollars in thousands) Amount Ownership % Amount Ownership %Gold Hill Venture Lending 03, LP (i) $9,413 9.3% $16,072 9.3%Gold Hill Capital 2008, LP (ii) 20,893 15.5 19,328 15.5China Joint Venture investment (iii) 78,545 50.0 — —Other investments 30,479 Various 32,852 VariousTotal other investments (equity method accounting) $139,330 $68,252

[4] Represents investments in 324 and 329 funds (primarily venture capital funds) at December 31, 2012 and December 31, 2011, respectively, where our ownership interest is less than 5% of the voting interests of each such fund and in which we do not have the ability to exercise significant influence over the partnerships operating activities and financial policies. For the year ended December 31, 2012, we recognized OTTI losses of $1.0 million resulting from other-than-temporary declines in value for 46 of the 324 investments. The OTTI losses are included in net gains on investment securities, a component of noninterest income. We concluded that any declines in value for the remaining investments were temporary and as such, no OTTI was required to be recognized. At December 31, 2012, the carrying value of these venture capital and private equity fund investments (cost method accounting) was $162 million, and the estimated fair value was $193 million.