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	Sep. 30, 2013	Dec. 31, 2012
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	$ 9,914,199	$ 9,024,248
Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	8,988,575	8,193,676
Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	925,624	830,572
Software
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	3,738,141	3,293,899
Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,153,393	1,129,484
Venture capital/private equity
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,953,161	1,749,903
Life science
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,108,061	1,076,792
Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	644,618	559,284
Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	391,201	384,314
Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	831,739	685,493
Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	93,885	145,079
Pass
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	9,229,209	8,428,907
Pass | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	8,318,025	7,632,178
Pass | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	911,184	796,729
Pass | Software
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	3,442,540	3,050,449
Pass | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	904,312	970,802
Pass | Venture capital/private equity
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,952,680	1,748,663
Pass | Life science
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,019,522	956,276
Pass | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	632,438	545,697
Pass | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	366,533	360,291
Pass | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	822,148	663,911
Pass | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	89,036	132,818
Performing (Criticized)
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	646,942	557,062
Performing (Criticized) | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	636,652	526,559
Performing (Criticized) | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	10,290	30,503
Performing (Criticized) | Software
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	292,560	240,187
Performing (Criticized) | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	221,635	136,819
Performing (Criticized) | Venture capital/private equity
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	434	1,240
Performing (Criticized) | Life science
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	88,539	120,516
Performing (Criticized) | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	10,704	9,189
Performing (Criticized) | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	22,780	18,608
Performing (Criticized) | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	6,252	19,343
Performing (Criticized) | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	4,038	11,160
Impaired
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	38,048	38,279
Impaired | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	33,898	34,939
Impaired | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	4,150	3,340
Impaired | Software
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	3,041	3,263
Impaired | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	27,446	21,863
Impaired | Venture capital/private equity
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	47	0
Impaired | Life science
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	0	0
Impaired | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,476	4,398
Impaired | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,888	5,415
Impaired | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	3,339	2,239
Impaired | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	$ 811	$ 1,101