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	Jun. 30, 2013	Dec. 31, 2012
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	$ 9,705,464	$ 9,024,248
Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	8,840,259	8,193,676
Commercial loans | Software
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	3,593,954	3,293,899
Commercial loans | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,217,613	1,129,484
Commercial loans | Venture capital/private equity
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,942,664	1,749,903
Commercial loans | Life science
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,095,581	1,076,792
Commercial loans | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	611,055	559,284
Commercial loans | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	379,392	384,314
Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	865,205	830,572
Consumer loans | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	778,310	685,493
Consumer loans | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	86,895	145,079
Pass
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	9,024,583	8,428,907
Pass | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	8,174,817	7,632,178
Pass | Commercial loans | Software
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	3,310,603	3,050,449
Pass | Commercial loans | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	973,721	970,802
Pass | Commercial loans | Venture capital/private equity
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,941,817	1,748,663
Pass | Commercial loans | Life science
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	992,121	956,276
Pass | Commercial loans | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	596,685	545,697
Pass | Commercial loans | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	359,870	360,291
Pass | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	849,766	796,729
Pass | Consumer loans | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	768,434	663,911
Pass | Consumer loans | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	81,332	132,818
Performing (Criticized)
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	639,722	557,062
Performing (Criticized) | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	628,856	526,559
Performing (Criticized) | Commercial loans | Software
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	276,719	240,187
Performing (Criticized) | Commercial loans | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	219,310	136,819
Performing (Criticized) | Commercial loans | Venture capital/private equity
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	758	1,240
Performing (Criticized) | Commercial loans | Life science
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	103,460	120,516
Performing (Criticized) | Commercial loans | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	12,859	9,189
Performing (Criticized) | Commercial loans | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	15,750	18,608
Performing (Criticized) | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	10,866	30,503
Performing (Criticized) | Consumer loans | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	6,257	19,343
Performing (Criticized) | Consumer loans | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	4,609	11,160
Impaired
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	41,159	38,279
Impaired | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	36,586	34,939
Impaired | Commercial loans | Software
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	6,632	3,263
Impaired | Commercial loans | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	24,582	21,863
Impaired | Commercial loans | Venture capital/private equity
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	89	0
Impaired | Commercial loans | Life science
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	0	0
Impaired | Commercial loans | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,511	4,398
Impaired | Commercial loans | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	3,772	5,415
Impaired | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	4,573	3,340
Impaired | Consumer loans | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	3,619	2,239
Impaired | Consumer loans | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	$ 954	$ 1,101