Investment Securities - Non-marketable and Other Securities (Detail) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018 USD ($) Investment	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($) Investment	Dec. 31, 2016
Investment Holdings [Line Items]
Amortization Method Qualified Affordable Housing Project Investments	$ 225,823		$ 174,214
Total non-marketable and other securities	$ 824,936		651,053
Upper Limit
Investment Holdings [Line Items]
Equity method investment voting ownership percentage	5.00%
Security Owned Not Readily Marketable, Name [Domain]
Investment Holdings [Line Items]
Unrealized Loss on Securities	$ (2,069)
Unrealized Gain (Loss) on Securities	4,214
Consolidated venture capital and private equity fund investments | Fair value accounting
Investment Holdings [Line Items]
Consolidated Nonmarketable Securities Investment Company Accounting	130,015		128,111
Consolidated venture capital and private equity fund investments | Equity method accounting
Investment Holdings [Line Items]
Non-marketable securities, equity method accounting	97,929		89,809
Debt funds | Equity method accounting
Investment Holdings [Line Items]
Non-marketable securities, equity method accounting	18,884		21,183
Other investments | Equity method accounting
Investment Holdings [Line Items]
Non-marketable securities, equity method accounting	112,115		111,198
Low income housing tax credit funds
Investment Holdings [Line Items]
Affordable Housing Tax Credits and Other Tax Benefits, Amount	5,422	$ 4,692
Amortization Method Qualified Affordable Housing Project Investments, Amortization	4,792	$ 3,236
Unconsolidated venture capital and private equity fund investments (1) | Fair value accounting | Silicon Valley BancVentures, LP
Investment Holdings [Line Items]
Consolidated Nonmarketable Securities Investment Company Accounting	$ 1,001		$ 919
Percentage of ownership	10.70%		10.70%
Debt funds | Equity method accounting
Investment Holdings [Line Items]
Non-marketable securities, equity method accounting	$ 18,884		$ 21,183
Debt funds | Equity method accounting | Gold Hill Capital 2008, LP
Investment Holdings [Line Items]
Non-marketable securities, equity method accounting	$ 15,978		18,690
Percentage of ownership	15.50%			15.50%
Debt funds | Equity method accounting | Other investments
Investment Holdings [Line Items]
Non-marketable securities, equity method accounting	$ 2,906		2,493
Other investments | Fair value accounting
Investment Holdings [Line Items]
Securities Owned Not Readily Marketable	29,825		27,680
Other investments | Equity method accounting
Investment Holdings [Line Items]
Non-marketable securities, equity method accounting	$ 112,115		111,198
Other investments | Equity method accounting | Gold Hill Capital 2008, LP | Direct ownership interest
Investment Holdings [Line Items]
Percentage of ownership	11.50%
Other investments | Equity method accounting | Gold Hill Capital 2008, LP | Indirect ownership interest
Investment Holdings [Line Items]
Percentage of ownership	4.00%
Other investments | Equity method accounting | China Joint Venture investment
Investment Holdings [Line Items]
Non-marketable securities, equity method accounting	$ 76,384		75,337
Percentage of ownership	50.00%			50.00%
Other investments | Equity method accounting | Other investments
Investment Holdings [Line Items]
Non-marketable securities, equity method accounting	$ 35,731		35,861
Consolidated venture capital and private equity fund investments | Fair value accounting
Investment Holdings [Line Items]
Consolidated Nonmarketable Securities Investment Company Accounting	130,015		128,111
Unconsolidated Nonmarketable Securities Investment Company Accounting	205,651		98,548
Consolidated venture capital and private equity fund investments | Fair value accounting | SVB Strategic Investors Fund, LP
Investment Holdings [Line Items]
Consolidated Nonmarketable Securities Investment Company Accounting	$ 14,767		$ 14,673
Percentage of ownership	12.60%		12.60%
Consolidated venture capital and private equity fund investments | Fair value accounting | SVB Capital Partners II, LP | Direct ownership interest
Investment Holdings [Line Items]
Percentage of ownership	1.30%
Consolidated venture capital and private equity fund investments | Fair value accounting | SVB Capital Partners II, LP | Indirect ownership interest
Investment Holdings [Line Items]
Percentage of ownership	3.80%
Consolidated venture capital and private equity fund investments | Fair value accounting | SVB Capital Preferred Return Fund, LP
Investment Holdings [Line Items]
Consolidated Nonmarketable Securities Investment Company Accounting	$ 56,541		$ 54,147
Percentage of ownership	20.00%		20.00%
Consolidated venture capital and private equity fund investments | Fair value accounting | SVB Capital—NT Growth Partners, LP
Investment Holdings [Line Items]
Consolidated Nonmarketable Securities Investment Company Accounting	$ 57,706		$ 58,372
Percentage of ownership	33.00%		33.00%
Consolidated venture capital and private equity fund investments | Equity method accounting
Investment Holdings [Line Items]
Non-marketable securities, equity method accounting	$ 97,929		$ 89,809
Consolidated venture capital and private equity fund investments | Equity method accounting | SVB Strategic Investors Fund II, LP
Investment Holdings [Line Items]
Non-marketable securities, equity method accounting	$ 5,653		6,342
Percentage of ownership	8.60%			8.60%
Consolidated venture capital and private equity fund investments | Equity method accounting | SVB Strategic Investors Fund III, LP
Investment Holdings [Line Items]
Non-marketable securities, equity method accounting	$ 18,480		18,758
Percentage of ownership	5.90%			5.90%
Consolidated venture capital and private equity fund investments | Equity method accounting | SVB Strategic Investors Fund IV, LP
Investment Holdings [Line Items]
Non-marketable securities, equity method accounting	$ 27,408		25,551
Percentage of ownership	5.00%			5.00%
Consolidated venture capital and private equity fund investments | Equity method accounting | Strategic Investors Fund V Funds
Investment Holdings [Line Items]
Non-marketable securities, equity method accounting	$ 20,497		16,856
Consolidated venture capital and private equity fund investments | Equity method accounting | SVB Capital Partners II, LP
Investment Holdings [Line Items]
Non-marketable securities, equity method accounting	$ 6,797		6,700
Percentage of ownership	5.10%			5.10%
Consolidated venture capital and private equity fund investments | Equity method accounting | Other investments
Investment Holdings [Line Items]
Non-marketable securities, equity method accounting	$ 19,094		$ 15,602
Consolidated venture capital and private equity fund investments | Cost method accounting
Investment Holdings [Line Items]
Number of investments | Investment	229		235