Investment Securities - Major Components of Investment Securities Portfolio (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013		Dec. 31, 2012
Investment Holdings [Line Items]
Amortized Cost	$ 10,047,354		$ 11,152,150
Unrealized Gains	97,112		192,960
Unrealized Losses	(101,125)		(1,933)
Carrying Value	10,043,341		11,343,177
Non-marketable securities	1,255,425		1,184,265
Total investment securities	11,298,766		12,527,442
Fair value accounting | Venture capital and private equity fund investments
Investment Holdings [Line Items]
Non-marketable securities	741,522		665,921	[1]
Fair value accounting | Other venture capital investments
Investment Holdings [Line Items]
Non-marketable securities	123,493		127,091
Equity method accounting | Other investments
Investment Holdings [Line Items]
Non-marketable securities	144,149		139,330
Equity method accounting | Low income housing tax credit funds
Investment Holdings [Line Items]
Non-marketable securities	71,382		70,318
Cost method accounting | Venture capital and private equity fund investments
Investment Holdings [Line Items]
Non-marketable securities	156,391	[2]	161,884
Cost method accounting | Other investments
Investment Holdings [Line Items]
Non-marketable securities	18,488		19,721
U.S. treasury securities
Investment Holdings [Line Items]
Amortized Cost	24,996		25,057
Unrealized Gains	3		190
Unrealized Losses	0		0
Carrying Value	24,999		25,247
U.S. agency debentures
Investment Holdings [Line Items]
Amortized Cost	3,386,664		3,370,455
Unrealized Gains	45,209		77,173
Unrealized Losses	(28,284)		0
Carrying Value	3,403,589		3,447,628
Residential mortgage-backed securities | Agency-issued mortgage-backed securities
Investment Holdings [Line Items]
Amortized Cost	1,197,489		1,428,682
Unrealized Gains	20,040		44,858
Unrealized Losses	(3,494)		(107)
Carrying Value	1,214,035		1,473,433
Residential mortgage-backed securities | Agency-issued collateralized mortgage obligations | Fixed rate
Investment Holdings [Line Items]
Amortized Cost	3,510,618		4,063,020
Unrealized Gains	15,844		41,949
Unrealized Losses	(57,780)		(995)
Carrying Value	3,468,682		4,103,974
Residential mortgage-backed securities | Agency-issued collateralized mortgage obligations | Variable rate
Investment Holdings [Line Items]
Amortized Cost	1,430,325		1,760,551
Unrealized Gains	8,447		12,201
Unrealized Losses	0		(4)
Carrying Value	1,438,772		1,772,748
Agency-issued commercial mortgage-backed securities
Investment Holdings [Line Items]
Amortized Cost	410,001		416,487
Unrealized Gains	2,331		6,100
Unrealized Losses	(11,128)		(489)
Carrying Value	401,204		422,098
Municipal bonds and notes
Investment Holdings [Line Items]
Amortized Cost	82,054		85,790
Unrealized Gains	4,947		7,750
Unrealized Losses	0		(11)
Carrying Value	87,001		93,529
Equity securities
Investment Holdings [Line Items]
Amortized Cost	5,207		2,108
Unrealized Gains	291		2,739
Unrealized Losses	(439)		(327)
Carrying Value	$ 5,059		$ 4,520

[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 June 30, 2013 and December 31, 2012 (fair value accounting): June 30, 2013 December 31, 2012(Dollars in thousands) Amount Ownership % Amount Ownership %SVB Strategic Investors Fund, LP $32,111 12.6% $32,850 12.6%SVB Strategic Investors Fund II, LP 93,110 8.6 91,294 8.6SVB Strategic Investors Fund III, LP 223,568 5.9 209,696 5.9SVB Strategic Investors Fund IV, LP 198,734 5.0 169,931 5.0Strategic Investors Fund V Funds 69,110 Various 40,622 VariousStrategic Investors Fund VI Funds 1,321 0.2 — —SVB Capital Preferred Return Fund, LP 56,140 20.0 53,643 20.0SVB Capital—NT Growth Partners, LP 60,775 33.0 60,120 33.0SVB Capital Partners II, LP (i) 1,098 5.1 1,303 5.1Other private equity fund (ii) 5,555 58.2 6,462 58.2Total venture capital and private equity fund investments $741,522 $665,921 (i)At June 30, 2013, we had a direct ownership interest of 1.3 percent and an indirect ownership interest of 3.8 percent in the fund through our ownership interest of SVB Strategic Investors Fund II, LP.(ii)At June 30, 2013, we had a direct ownership interest of 41.5 percent and indirect ownership interests of 12.6 percent and 4.1 percent in the fund through our ownership interest of SVB Capital—NT Growth Partners, LP and SVB Capital Preferred Return Fund, LP, respectively.

[2] Represents investments in 303 and 324 funds (primarily venture capital funds) at June 30, 2013 and December 31, 2012, respectively, where our ownership interest is typically 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 three months ended June 30, 2013, we recognized OTTI losses of $0.3 million resulting from other-than-temporary declines in value for 12 of the 303 investments. For the six months ended June 30, 2013, we recognized OTTI losses of $0.8 million resulting from other-than-temporary declines in value for 27 of the 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 June 30, 2013, the carrying value of these venture capital and private equity fund investments (cost method accounting) was $156 million, and the estimated fair value was $204 million.