Loans and Allowance for Loan Losses - Activity in Allowance for Loan Losses Broken out by Portfolio Segment (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015		Sep. 30, 2014
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	$ 192,644	$ 120,728	$ 165,359		$ 142,886
Charge-offs	(29,118)	(10,657)	(39,339)		(38,189)
Recoveries	578	2,380	5,119		5,313
Provision for loan losses	33,403	16,610	66,368	[1]	19,051
Ending Balance	197,507	129,061	197,507		129,061
Commercial Portfolio Segment | Software and internet
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	106,728	53,239	80,981		64,084
Charge-offs	(24,815)	(6,907)	(26,980)		(18,932)
Recoveries	195	790	1,239		1,023
Provision for loan losses	5,958	11,078	32,826		12,025
Ending Balance	88,066	58,200	88,066		58,200
Commercial Portfolio Segment | Hardware
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	20,472	24,780	25,860		36,553
Charge-offs	0	(2,643)	(4,049)		(15,230)
Recoveries	240	113	3,049		2,070
Provision for loan losses	(70)	2,491	(4,218)		1,348
Ending Balance	20,642	24,741	20,642		24,741
Commercial Portfolio Segment | Private equity/venture capital
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	29,276	19,004	27,997		16,385
Charge-offs	0	0	0		0
Recoveries	0	0	0		0
Provision for loan losses	3,166	845	4,445		3,464
Ending Balance	32,442	19,849	32,442		19,849
Commercial Portfolio Segment | Life science & healthcare
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	17,233	10,597	15,208		11,926
Charge-offs	(117)	0	(3,336)		(930)
Recoveries	50	53	129		341
Provision for loan losses	19,793	1,591	24,958		904
Ending Balance	36,959	12,241	36,959		12,241
Commercial Portfolio Segment | Premium wine
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	4,409	3,546	4,473		3,914
Charge-offs	0	(35)	0		(35)
Recoveries	0	0	7		238
Provision for loan losses	253	710	182		104
Ending Balance	4,662	4,221	4,662		4,221
Commercial Portfolio Segment | Other
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	5,894	3,218	3,253		3,680
Charge-offs	(4,186)	(1,072)	(4,974)		(3,062)
Recoveries	89	1,306	559		1,316
Provision for loan losses	2,976	(530)	5,935		988
Ending Balance	4,773	2,922	4,773		2,922
Commercial Portfolio Segment | Commercial loans
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	184,012	114,384	157,772		136,542
Charge-offs	(29,118)	(10,657)	(39,339)		(38,189)
Recoveries	574	2,262	4,983		4,988
Provision for loan losses	32,076	16,185	64,128		18,833
Ending Balance	187,544	122,174	187,544		122,174
Consumer Portfolio Segment | Consumer loans
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	8,632	6,344	7,587		6,344
Charge-offs	0	0	0		0
Recoveries	4	118	136		325
Provision for loan losses	1,327	425	2,240		218
Ending Balance	$ 9,963	$ 6,887	$ 9,963		$ 6,887

[1] Amounts for the nine months ended September 30, 2015, have been revised to reflect the retrospective application of new accounting guidance adopted in the second quarter of 2015 related to our consolidated variable interest entities (ASU 2015-02). Amounts prior to January 1, 2015 have not been revised for the adoption of this guidance. See Note 1— "Basis of Presentation” of the “Notes to Interim Consolidated Financial Statements (unaudited)” under Part I, Item 1 of this report for additional details.