Loans and Allowance for Loan Losses - Activity in Allowance for Loan Losses Broken out by Portfolio Segment (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance				$ 165,359				$ 142,886	$ 165,359	$ 142,886	$ 110,651
Charge-offs									(50,968)	(43,168)	(42,666)
Recoveries									5,593	6,155	11,208
Provision for loan losses	$ 31,261	$ 33,403	$ 26,513	6,452	$ 40,435	$ 16,610	$ 1,947	494	97,629	59,486	63,693
Ending Balance	217,613				165,359				217,613	165,359	142,886
Software and internet
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance								64,084		64,084	42,648
Charge-offs											(8,861)
Recoveries											1,934
Provision for loan losses											28,363
Ending Balance											64,084
Hardware
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance								36,553		36,553	29,761
Charge-offs											(18,819)
Recoveries											2,677
Provision for loan losses											22,934
Ending Balance											36,553
Private equity/venture capital
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance								16,385		16,385	9,963
Charge-offs											0
Recoveries											0
Provision for loan losses											6,422
Ending Balance											16,385
Life science/healthcare
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance								11,926		11,926	13,606
Charge-offs											(6,010)
Recoveries											1,860
Provision for loan losses											2,470
Ending Balance											11,926
Premium wine
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance								3,914		3,914	3,523
Charge-offs											0
Recoveries											170
Provision for loan losses											221
Ending Balance											3,914
Other
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance								3,680		3,680	3,912
Charge-offs											(8,107)
Recoveries											2,995
Provision for loan losses											4,880
Ending Balance											3,680
Commercial loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance				157,772				136,542	157,772	136,542	103,413
Charge-offs									(50,672)	(43,168)	(41,797)
Recoveries									5,430	5,776	9,636
Provision for loan losses									94,915	58,622	65,290
Ending Balance	207,445				157,772				207,445	157,772	136,542
Commercial loans | Software and internet
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance				80,981				64,084	80,981	64,084
Charge-offs									(33,246)	(21,031)
Recoveries									1,621	1,425
Provision for loan losses									53,689	36,503
Ending Balance	103,045				80,981				103,045	80,981	64,084
Commercial loans | Hardware
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance				25,860				36,553	25,860	36,553
Charge-offs									(5,145)	(15,265)
Recoveries									3,332	2,238
Provision for loan losses									(962)	2,334
Ending Balance	23,085				25,860				23,085	25,860	36,553
Commercial loans | Private equity/venture capital
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance				27,997				16,385	27,997	16,385
Charge-offs									0	0
Recoveries									0	0
Provision for loan losses									7,285	11,612
Ending Balance	35,282				27,997				35,282	27,997	16,385
Commercial loans | Life science/healthcare
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance				15,208				11,926	15,208	11,926
Charge-offs									(7,291)	(2,951)
Recoveries									277	374
Provision for loan losses									28,382	5,859
Ending Balance	36,576				15,208				36,576	15,208	11,926
Commercial loans | Premium wine
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance				4,473				3,914	4,473	3,914
Charge-offs									0	(35)
Recoveries									7	240
Provision for loan losses									725	354
Ending Balance	5,205				4,473				5,205	4,473	3,914
Commercial loans | Other
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance				3,253				3,680	3,253	3,680
Charge-offs									(4,990)	(3,886)
Recoveries									193	1,499
Provision for loan losses									5,796	1,960
Ending Balance	4,252				3,253				4,252	3,253	3,680
Consumer loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance				$ 7,587				$ 6,344	7,587	6,344	7,238
Charge-offs									(296)	0	(869)
Recoveries									163	379	1,572
Provision for loan losses									2,714	864	(1,597)
Ending Balance	$ 10,168				$ 7,587				$ 10,168	$ 7,587	$ 6,344