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
	Mar. 31, 2015	Mar. 31, 2014
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	$ 165,359	$ 142,886
Charge-offs	(5,487)	(21,150)
Recoveries	1,551	1,312
Provision for (Reduction of) Loan Losses	6,452	494
Ending Balance	167,875	123,542
Software and internet
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	80,981	64,084
Charge-offs	(1,403)	(8,010)
Recoveries	447	114
Provision for (Reduction of) Loan Losses	2,067	(947)
Ending Balance	82,092	55,241
Hardware
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	25,860	36,553
Charge-offs	(3,210)	(12,175)
Recoveries	928	775
Provision for (Reduction of) Loan Losses	(2,320)	83
Ending Balance	21,258	25,236
Private equity/venture capital
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	27,997	16,385
Charge-offs	0	0
Recoveries	0	0
Provision for (Reduction of) Loan Losses	2,840	1,291
Ending Balance	30,837	17,676
Life science & healthcare
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	15,208	11,926
Charge-offs	(225)	(681)
Recoveries	34	98
Provision for (Reduction of) Loan Losses	306	131
Ending Balance	15,323	11,474
Premium wine
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	4,473	3,914
Charge-offs	0	0
Recoveries	0	219
Provision for (Reduction of) Loan Losses	30	(396)
Ending Balance	4,503	3,737
Other
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	3,253	3,680
Charge-offs	(649)	(284)
Recoveries	10	0
Provision for (Reduction of) Loan Losses	3,537	645
Ending Balance	6,151	4,041
Commercial loans
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	157,772	136,542
Charge-offs	(5,487)	(21,150)
Recoveries	1,419	1,206
Provision for (Reduction of) Loan Losses	6,460	807
Ending Balance	160,164	117,405
Consumer loans
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	7,587	6,344
Charge-offs	0	0
Recoveries	132	106
Provision for (Reduction of) Loan Losses	(8)	(313)
Ending Balance	$ 7,711	$ 6,137