Loans and Allowance for Loan Losses - Average Impaired Loans, Broken out by Portfolio Segment and Class of Financing Receivable (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Financing Receivable, Impaired [Line Items]
Average impaired loans	$ 15,035	$ 39,279	$ 25,846	$ 40,719
Software
Financing Receivable, Impaired [Line Items]
Average impaired loans	10,651	4,306	13,690	4,631
Hardware
Financing Receivable, Impaired [Line Items]
Average impaired loans	1,540	25,456	8,140	24,536
Venture capital/private equity
Financing Receivable, Impaired [Line Items]
Average impaired loans	0	75	0	35
Life science
Financing Receivable, Impaired [Line Items]
Average impaired loans	333	0	636	303
Premium wine
Financing Receivable, Impaired [Line Items]
Average impaired loans	1,364	1,502	1,398	2,458
Other
Financing Receivable, Impaired [Line Items]
Average impaired loans	674	3,648	1,383	4,344
Commercial loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	14,562	34,987	25,247	36,307
Real estate secured loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	212	3,426	224	3,391
Consumer loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	261	866	375	1,021
Consumer loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	$ 473	$ 4,292	$ 599	$ 4,412