Loans and Allowance for Loan Losses - Credit Quality Indicators, Broken out by Portfolio Segment and Class of Financing Receivables (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	$ 8,922,829	$ 9,024,248
Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	8,098,722	8,193,676
Commercial loans | Software
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	3,490,963	3,293,899
Commercial loans | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,233,181	1,129,484
Commercial loans | Venture capital/private equity
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,335,561	1,749,903
Commercial loans | Life science
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,028,275	1,076,792
Commercial loans | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	606,386	559,284
Commercial loans | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	404,356	384,314
Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	824,107	830,572
Consumer loans | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	724,849	685,493
Consumer loans | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	99,258	145,079
Pass
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	8,352,295	8,428,907
Pass | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	7,559,457	7,632,178
Pass | Commercial loans | Software
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	3,250,004	3,050,449
Pass | Commercial loans | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,084,742	970,802
Pass | Commercial loans | Venture capital/private equity
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,334,740	1,748,663
Pass | Commercial loans | Life science
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	916,649	956,276
Pass | Commercial loans | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	590,448	545,697
Pass | Commercial loans | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	382,874	360,291
Pass | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	792,838	796,729
Pass | Consumer loans | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	700,850	663,911
Pass | Consumer loans | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	91,988	132,818
Performing (Criticized)
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	526,188	557,062
Performing (Criticized) | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	500,454	526,559
Performing (Criticized) | Commercial loans | Software
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	234,865	240,187
Performing (Criticized) | Commercial loans | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	125,773	136,819
Performing (Criticized) | Commercial loans | Venture capital/private equity
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	821	1,240
Performing (Criticized) | Commercial loans | Life science
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	111,172	120,516
Performing (Criticized) | Commercial loans | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	11,635	9,189
Performing (Criticized) | Commercial loans | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	16,188	18,608
Performing (Criticized) | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	25,734	30,503
Performing (Criticized) | Consumer loans | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	19,556	19,343
Performing (Criticized) | Consumer loans | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	6,178	11,160
Impaired
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	44,346	38,279
Impaired | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	38,811	34,939
Impaired | Commercial loans | Software
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	6,094	3,263
Impaired | Commercial loans | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	22,666	21,863
Impaired | Commercial loans | Venture capital/private equity
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	0	0
Impaired | Commercial loans | Life science
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	454	0
Impaired | Commercial loans | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	4,303	4,398
Impaired | Commercial loans | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	5,294	5,415
Impaired | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	5,535	3,340
Impaired | Consumer loans | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	4,443	2,239
Impaired | Consumer loans | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	$ 1,092	$ 1,101