Loans and Allowance for Loan Losses - Activity in Allowance for Loan Losses Broken out by Portfolio Segment (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015		Jun. 30, 2014
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	$ 167,875	$ 123,542	$ 165,359		$ 142,886
Charge-offs	(4,734)	(6,382)	(10,221)		(27,532)
Recoveries	2,990	1,621	4,541		2,933
Provision for loan losses	26,513	1,947	32,965	[1]	2,441
Ending Balance	192,644	120,728	192,644		120,728
Commercial Portfolio Segment | Software and internet
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	82,092	55,241	80,981		64,084
Charge-offs	(762)	(4,015)	(2,165)		(12,025)
Recoveries	597	119	1,044		233
Provision for loan losses	24,801	1,894	26,868		947
Ending Balance	106,728	53,239	106,728		53,239
Commercial Portfolio Segment | Hardware
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	21,258	25,236	25,860		36,553
Charge-offs	(839)	(412)	(4,049)		(12,587)
Recoveries	1,881	1,182	2,809		1,957
Provision for loan losses	(1,828)	(1,226)	(4,148)		(1,143)
Ending Balance	20,472	24,780	20,472		24,780
Commercial Portfolio Segment | Private equity/venture capital
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	30,837	17,676	27,997		16,385
Charge-offs	0	0	0		0
Recoveries	0	0	0		0
Provision for loan losses	(1,561)	1,328	1,279		2,619
Ending Balance	29,276	19,004	29,276		19,004
Commercial Portfolio Segment | Life science & healthcare
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	15,323	11,474	15,208		11,926
Charge-offs	(2,994)	(249)	(3,219)		(930)
Recoveries	45	190	79		288
Provision for loan losses	4,859	(818)	5,165		(687)
Ending Balance	17,233	10,597	17,233		10,597
Commercial Portfolio Segment | Premium wine
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	4,503	3,737	4,473		3,914
Charge-offs	0	0	0		0
Recoveries	7	19	7		238
Provision for loan losses	(101)	(210)	(71)		(606)
Ending Balance	4,409	3,546	4,409		3,546
Commercial Portfolio Segment | Other
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	6,151	4,041	3,253		3,680
Charge-offs	(139)	(1,706)	(788)		(1,990)
Recoveries	460	10	470		10
Provision for loan losses	(578)	873	2,959		1,518
Ending Balance	5,894	3,218	5,894		3,218
Commercial Portfolio Segment | Commercial loans
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	160,164	117,405	157,772		136,542
Charge-offs	(4,734)	(6,382)	(10,221)		(27,532)
Recoveries	2,990	1,520	4,409		2,726
Provision for loan losses	25,592	1,841	32,052		2,648
Ending Balance	184,012	114,384	184,012		114,384
Consumer Portfolio Segment | Consumer loans
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	7,711	6,137	7,587		6,344
Charge-offs	0	0	0		0
Recoveries	0	101	132		207
Provision for loan losses	921	106	913		(207)
Ending Balance	$ 8,632	$ 6,344	$ 8,632		$ 6,344

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