Loans and Allowance for Loan Losses - Impaired Loans and Allowance for Loan Losses, Broken out by Portfolio Segment and Class of Financing Receivable (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	$ 178,462	$ 182,684
Total unpaid principal of impaired loans	195,449	213,190
Impaired loans for which there is a related allowance for loan losses
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	176,555	180,592
Impaired loans for which there is no related allowance for loan losses
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	1,907	2,092
Commercial Portfolio Segment | Software and internet
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	109,432	100,866
Total unpaid principal of impaired loans	122,585	125,494
Commercial Portfolio Segment | Hardware
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	27,916	27,736
Total unpaid principal of impaired loans	28,764	27,869
Commercial Portfolio Segment | Private equity/venture capital
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	0	0
Total unpaid principal of impaired loans	0	0
Commercial Portfolio Segment | Life science/healthcare
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	33,040	51,354
Total unpaid principal of impaired loans	34,205	55,310
Commercial Portfolio Segment | Premium wine
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	2,427	2,065
Total unpaid principal of impaired loans	2,991	2,604
Commercial Portfolio Segment | Commercial loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	178,331	182,541
Total unpaid principal of impaired loans	194,061	211,797
Commercial Portfolio Segment | Other
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	5,516	520
Total unpaid principal of impaired loans	5,516	520
Commercial Portfolio Segment | Impaired loans for which there is a related allowance for loan losses | Software and internet
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	108,871	100,866
Commercial Portfolio Segment | Impaired loans for which there is a related allowance for loan losses | Hardware
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	27,702	27,736
Commercial Portfolio Segment | Impaired loans for which there is a related allowance for loan losses | Private equity/venture capital
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	0	0
Commercial Portfolio Segment | Impaired loans for which there is a related allowance for loan losses | Life science/healthcare
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	33,040	50,429
Commercial Portfolio Segment | Impaired loans for which there is a related allowance for loan losses | Premium wine
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	1,295	898
Commercial Portfolio Segment | Impaired loans for which there is a related allowance for loan losses | Commercial loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	176,424	180,449
Commercial Portfolio Segment | Impaired loans for which there is a related allowance for loan losses | Other
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	5,516	520
Commercial Portfolio Segment | Impaired loans for which there is no related allowance for loan losses | Software and internet
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	561	0
Commercial Portfolio Segment | Impaired loans for which there is no related allowance for loan losses | Hardware
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	214	0
Commercial Portfolio Segment | Impaired loans for which there is no related allowance for loan losses | Private equity/venture capital
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	0	0
Commercial Portfolio Segment | Impaired loans for which there is no related allowance for loan losses | Life science/healthcare
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	0	925
Commercial Portfolio Segment | Impaired loans for which there is no related allowance for loan losses | Premium wine
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	1,132	1,167
Commercial Portfolio Segment | Impaired loans for which there is no related allowance for loan losses | Commercial loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	1,907	2,092
Commercial Portfolio Segment | Impaired loans for which there is no related allowance for loan losses | Other
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	0	0
Consumer Portfolio Segment | Other
Financing Receivable, Impaired [Line Items]
Total unpaid principal of impaired loans	0	0
Consumer Portfolio Segment | Real estate secured loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	131	143
Total unpaid principal of impaired loans	1,388	1,393
Consumer Portfolio Segment | Other consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	0	0
Consumer Portfolio Segment | Consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	131	143
Total unpaid principal of impaired loans	1,388	1,393
Consumer Portfolio Segment | Impaired loans for which there is a related allowance for loan losses | Other
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	0	0
Consumer Portfolio Segment | Impaired loans for which there is a related allowance for loan losses | Real estate secured loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	131	143
Consumer Portfolio Segment | Impaired loans for which there is a related allowance for loan losses | Consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	131	143
Consumer Portfolio Segment | Impaired loans for which there is no related allowance for loan losses | Other
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	0	0
Consumer Portfolio Segment | Impaired loans for which there is no related allowance for loan losses | Real estate secured loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	0	0
Consumer Portfolio Segment | Impaired loans for which there is no related allowance for loan losses | Consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	$ 0	$ 0