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								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance				$ 142,886				$ 110,651	$ 142,886	$ 110,651	$ 89,947
Charge-offs									(43,168)	(42,666)	(33,319)
Recoveries									6,155	11,208	9,693
Provision for (Reduction of)	40,435	16,610	1,947	494	28,670	10,638	18,572	5,813	59,486	63,693	44,330
Ending Balance	165,359				142,886				165,359	142,886	110,651
Hardware
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance				36,553				29,761	36,553	29,761	16,810
Charge-offs									(15,265)	(18,819)	(20,247)
Recoveries									2,238	2,677	1,107
Provision for (Reduction of)									2,334	22,934	32,091
Ending Balance	25,860				36,553				25,860	36,553	29,761
Software and internet
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance				64,084				42,648	64,084	42,648	38,263
Charge-offs									(21,031)	(8,861)	(4,316)
Recoveries									1,425	1,934	4,874
Provision for (Reduction of)									36,503	28,363	3,827
Ending Balance	80,981				64,084				80,981	64,084	42,648
Venture capital/private equity
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance				16,385				9,963	16,385	9,963	7,319
Charge-offs									0	0	0
Recoveries									0	0	0
Provision for (Reduction of)									11,612	6,422	2,644
Ending Balance	27,997				16,385				27,997	16,385	9,963
Life science
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance				11,926				13,606	11,926	13,606	10,243
Charge-offs									(2,951)	(6,010)	(5,080)
Recoveries									374	1,860	334
Provision for (Reduction of)									5,859	2,470	8,109
Ending Balance	15,208				11,926				15,208	11,926	13,606
Premium wine
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance				3,914				3,523	3,914	3,523	3,914
Charge-offs									(35)	0	(584)
Recoveries									240	170	650
Provision for (Reduction of)									354	221	(457)
Ending Balance	4,473				3,914				4,473	3,914	3,523
Commercial, Other
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance				3,680				3,912	3,680	3,912	5,817
Charge-offs									(3,886)	(8,107)	(2,485)
Recoveries									1,499	2,995	1,377
Provision for (Reduction of)									1,960	4,880	(797)
Ending Balance	3,253				3,680				3,253	3,680	3,912
Commercial loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance				136,542				103,413	136,542	103,413	82,366
Charge-offs									(43,168)	(41,797)	(32,712)
Recoveries									5,776	9,636	8,342
Provision for (Reduction of)									58,622	65,290	45,417
Ending Balance	157,772				136,542				157,772	136,542	103,413
Consumer loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance				6,344				7,238	6,344	7,238	7,581
Charge-offs									0	(869)	(607)
Recoveries									379	1,572	1,351
Provision for (Reduction of)									864	(1,597)	(1,087)
Ending Balance	$ 7,587				$ 6,344				$ 7,587	$ 6,344	$ 7,238