Impaired Loans and Allowance for Loan Losses, Broken out by Portfolio Segment and Class of Financing Receivable (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	$ 39,397	$ 36,617
Total unpaid principal of impaired loans	64,728	48,958
Commercial loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	35,769	15,201
Total unpaid principal of impaired loans	55,950	23,351
Commercial loans | Software
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	2,816	1,142
Total unpaid principal of impaired loans	3,324	1,540
Commercial loans | Hardware
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	27,129	5,183
Total unpaid principal of impaired loans	42,415	8,843
Commercial loans | Life science
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	0	311
Total unpaid principal of impaired loans	0	523
Commercial loans | Premium wine
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	3,079	3,212
Total unpaid principal of impaired loans	3,317	3,341
Commercial loans | Commercial Other Financing Receivable
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	2,745	5,353
Total unpaid principal of impaired loans	6,894	9,104
Consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	3,628	21,416
Total unpaid principal of impaired loans	8,778	25,607
Consumer loans | Real estate secured loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	2,408	18,283
Total unpaid principal of impaired loans	7,407	22,410
Consumer loans | Consumer Other Financing Receivable
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	1,220	3,133
Total unpaid principal of impaired loans	1,371	3,197
Impaired loans for which there is no related allowance for loan losses
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	8,294	23,285
Impaired loans for which there is no related allowance for loan losses | Commercial loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	6,006	5,002
Impaired loans for which there is no related allowance for loan losses | Commercial loans | Software
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	182	0
Impaired loans for which there is no related allowance for loan losses | Commercial loans | Hardware
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	0	429
Impaired loans for which there is no related allowance for loan losses | Commercial loans | Life science
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	0	311
Impaired loans for which there is no related allowance for loan losses | Commercial loans | Premium wine
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	3,079	3,212
Impaired loans for which there is no related allowance for loan losses | Commercial loans | Commercial Other Financing Receivable
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	2,745	1,050
Impaired loans for which there is no related allowance for loan losses | Consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	2,288	18,283
Impaired loans for which there is no related allowance for loan losses | Consumer loans | Real estate secured loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	2,288	18,283
Impaired loans for which there is no related allowance for loan losses | Consumer loans | Consumer Other Financing Receivable
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	0	0
Impaired loans for which there is a related allowance for loan losses
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	31,103	13,332
Impaired loans for which there is a related allowance for loan losses | Commercial loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	29,763	10,199
Impaired loans for which there is a related allowance for loan losses | Commercial loans | Software
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	2,634	1,142
Impaired loans for which there is a related allowance for loan losses | Commercial loans | Hardware
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	27,129	4,754
Impaired loans for which there is a related allowance for loan losses | Commercial loans | Life science
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	0	0
Impaired loans for which there is a related allowance for loan losses | Commercial loans | Premium wine
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	0	0
Impaired loans for which there is a related allowance for loan losses | Commercial loans | Commercial Other Financing Receivable
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	0	4,303
Impaired loans for which there is a related allowance for loan losses | Consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	1,340	3,133
Impaired loans for which there is a related allowance for loan losses | Consumer loans | Real estate secured loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	120	0
Impaired loans for which there is a related allowance for loan losses | Consumer loans | Consumer Other Financing Receivable
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	$ 1,220	$ 3,133