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	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Financing Receivable, Impaired [Line Items]
Average impaired loans	$ 24,516	$ 40,846	$ 35,814
Software and internet
Financing Receivable, Impaired [Line Items]
Average impaired loans	14,357	6,254	2,223
Hardware
Financing Receivable, Impaired [Line Items]
Average impaired loans	6,634	24,508	19,242
Venture capital/private equity
Financing Receivable, Impaired [Line Items]
Average impaired loans	0	37	0
Life science
Financing Receivable, Impaired [Line Items]
Average impaired loans	516	334	345
Premium wine
Financing Receivable, Impaired [Line Items]
Average impaired loans	1,381	2,210	3,513
Commercial, Other
Financing Receivable, Impaired [Line Items]
Average impaired loans	1,088	3,601	3,558
Commercial loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	23,976	36,944	28,881
Real estate secured loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	218	2,957	5,037
Consumer, Other
Financing Receivable, Impaired [Line Items]
Average impaired loans	322	945	1,896
Consumer loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	$ 540	$ 3,902	$ 6,933