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
	Mar. 31, 2015	Mar. 31, 2014
Financing Receivable, Impaired [Line Items]
Average impaired loans	$ 39,472	$ 35,655
Software and internet
Financing Receivable, Impaired [Line Items]
Average impaired loans	33,725	14,677
Hardware
Financing Receivable, Impaired [Line Items]
Average impaired loans	1,643	16,020
Life science & healthcare
Financing Receivable, Impaired [Line Items]
Average impaired loans	400	1,022
Premium wine
Financing Receivable, Impaired [Line Items]
Average impaired loans	1,282	1,433
Other
Financing Receivable, Impaired [Line Items]
Average impaired loans	2,139	1,777
Commercial loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	39,189	34,929
Real estate secured loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	195	237
Consumer loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	88	489
Consumer loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	$ 283	$ 726