Activity in Allowance for Loan Losses Broken out by Portfolio Segment (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	$ 98,166	$ 82,155	$ 89,947	$ 82,627
Charge-offs	(4,637)	(8,248)	(25,757)	(16,863)
Recoveries	1,207	10,570	8,018	21,626
Provision for (Reduction of)	6,788	769	29,316	(2,144)
Ending Balance	101,524	85,246	101,524	85,246
Commercial loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	90,263	73,325	82,366	72,104
Charge-offs	(4,637)	(8,248)	(25,150)	(16,863)
Recoveries	741	6,545	6,992	17,042
Provision for (Reduction of)	7,787	3,883	29,946	3,222
Ending Balance	94,154	75,505	94,154	75,505
Commercial loans | Software
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	37,981	31,873	38,263	29,288
Charge-offs	0	(3,125)	(2,977)	(4,747)
Recoveries	374	2,718	4,462	10,638
Provision for (Reduction of)	(1,110)	4,899	(2,503)	1,186
Ending Balance	37,245	36,365	37,245	36,365
Commercial loans | Hardware
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	22,632	16,042	16,810	14,688
Charge-offs	(1,849)	(4,813)	(16,110)	(4,828)
Recoveries	106	44	540	356
Provision for (Reduction of)	6,796	2,304	26,445	3,361
Ending Balance	27,685	13,577	27,685	13,577
Commercial loans | Venture capital/private equity
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	9,652	8,307	7,319	8,241
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provision for (Reduction of)	991	(497)	3,324	(431)
Ending Balance	10,643	7,810	10,643	7,810
Commercial loans | Life science
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	11,660	7,225	10,243	9,077
Charge-offs	(2,781)	(310)	(3,016)	(3,972)
Recoveries	3	3,359	316	4,487
Provision for (Reduction of)	3,281	(2,110)	4,620	(1,428)
Ending Balance	12,163	8,164	12,163	8,164
Commercial loans | Premium wine
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	3,396	4,009	3,914	5,492
Charge-offs	0	0	(584)	(449)
Recoveries	228	360	493	1,090
Provision for (Reduction of)	(463)	(354)	(662)	(2,118)
Ending Balance	3,161	4,015	3,161	4,015
Commercial loans | Commercial Other Financing Receivable
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	4,942	5,869	5,817	5,318
Charge-offs	(7)	0	(2,463)	(2,867)
Recoveries	30	64	1,181	471
Provision for (Reduction of)	(1,708)	(359)	(1,278)	2,652
Ending Balance	3,257	5,574	3,257	5,574
Consumer loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	7,903	8,830	7,581	10,523
Charge-offs	0	0	(607)	0
Recoveries	466	4,025	1,026	4,584
Provision for (Reduction of)	(999)	(3,114)	(630)	(5,366)
Ending Balance	$ 7,370	$ 9,741	$ 7,370	$ 9,741