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, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Financing Receivable, Impaired [Line Items]
Average impaired loans	$ 30,568	$ 39,871	$ 34,568	$ 36,879
Commercial loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	26,891	20,018	26,449	17,034
Commercial loans | Software
Financing Receivable, Impaired [Line Items]
Average impaired loans	2,689	2,562	2,040	2,652
Commercial loans | Hardware
Financing Receivable, Impaired [Line Items]
Average impaired loans	18,490	7,071	17,407	6,086
Commercial loans | Life science
Financing Receivable, Impaired [Line Items]
Average impaired loans	0	827	78	1,498
Commercial loans | Premium wine
Financing Receivable, Impaired [Line Items]
Average impaired loans	3,093	1,954	3,334	2,345
Commercial loans | Commercial Other Financing Receivable
Financing Receivable, Impaired [Line Items]
Average impaired loans	2,619	7,604	3,590	4,453
Consumer loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	3,677	19,853	8,119	19,845
Consumer loans | Real estate secured loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	2,411	18,746	5,967	19,476
Consumer loans | Consumer Other Financing Receivable
Financing Receivable, Impaired [Line Items]
Average impaired loans	$ 1,266	$ 1,107	$ 2,152	$ 369