Loans and Allowance for Loan Losses - Activity in Allowance for Loan Losses Broken out by Portfolio Segment (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	$ 112,205	$ 100,922	$ 110,651	$ 89,947
Charge-offs	(15,375)	(14,130)	(21,001)	(21,120)
Recoveries	4,169	3,375	5,536	6,811
Provision for (Reduction of) Loan Losses	18,572	7,999	24,385	22,528
Ending Balance	119,571	98,166	119,571	98,166
Commercial loans
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	104,981	91,819	103,413	82,366
Charge-offs	(14,506)	(13,523)	(20,132)	(20,513)
Recoveries	4,102	3,044	5,089	6,251
Provision for (Reduction of) Loan Losses	18,190	8,923	24,397	22,159
Ending Balance	112,767	90,263	112,767	90,263
Commercial loans | Software
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	45,010	35,425	42,648	38,263
Charge-offs	(3,574)	(2,118)	(5,092)	(2,977)
Recoveries	397	1,329	639	4,088
Provision for (Reduction of) Loan Losses	4,965	3,345	8,603	(1,393)
Ending Balance	46,798	37,981	46,798	37,981
Commercial loans | Hardware
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	27,869	30,348	29,761	16,810
Charge-offs	(4,434)	(10,413)	(6,431)	(14,261)
Recoveries	403	329	849	434
Provision for (Reduction of) Loan Losses	9,350	2,368	9,009	19,649
Ending Balance	33,188	22,632	33,188	22,632
Commercial loans | Venture capital/private equity
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	10,482	7,214	9,963	7,319
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provision for (Reduction of) Loan Losses	3,111	2,438	3,630	2,333
Ending Balance	13,593	9,652	13,593	9,652
Commercial loans | Life science
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	13,946	10,292	13,606	10,243
Charge-offs	(491)	(122)	(2,561)	(235)
Recoveries	886	92	1,089	313
Provision for (Reduction of) Loan Losses	(2,600)	1,398	(393)	1,339
Ending Balance	11,741	11,660	11,741	11,660
Commercial loans | Premium wine
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	3,699	3,738	3,523	3,914
Charge-offs	0	(584)	0	(584)
Recoveries	41	187	131	265
Provision for (Reduction of) Loan Losses	53	55	139	(199)
Ending Balance	3,793	3,396	3,793	3,396
Commercial loans | Other
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	3,975	4,802	3,912	5,817
Charge-offs	(6,007)	(286)	(6,048)	(2,456)
Recoveries	2,375	1,107	2,381	1,151
Provision for (Reduction of) Loan Losses	3,311	(681)	3,409	430
Ending Balance	3,654	4,942	3,654	4,942
Consumer loans
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	7,224	9,103	7,238	7,581
Charge-offs	(869)	(607)	(869)	(607)
Recoveries	67	331	447	560
Provision for (Reduction of) Loan Losses	382	(924)	(12)	369
Ending Balance	$ 6,804	$ 7,903	$ 6,804	$ 7,903