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	Sep. 30, 2016	Dec. 31, 2015
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	$ 167,147	$ 182,684
Total unpaid principal of impaired loans	190,184	213,190
Impaired loans for which there is a related allowance for loan losses
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	166,478	180,592
Impaired loans for which there is no related allowance for loan losses
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	669	2,092
Commercial Portfolio Segment | Software and internet
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	57,831	100,866
Total unpaid principal of impaired loans	76,679	125,494
Commercial Portfolio Segment | Hardware
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	49,356	27,736
Total unpaid principal of impaired loans	49,393	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	54,341	51,354
Total unpaid principal of impaired loans	57,222	55,310
Commercial Portfolio Segment | Premium wine
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	1,285	2,065
Total unpaid principal of impaired loans	1,285	2,604
Commercial Portfolio Segment | Other
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	417	520
Total unpaid principal of impaired loans	417	520
Commercial Portfolio Segment | Commercial loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	163,230	182,541
Total unpaid principal of impaired loans	184,996	211,797
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	57,831	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	48,687	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	54,341	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	1,285	898
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	417	520
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	162,561	180,449
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	0	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	669	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	0	1,167
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
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	669	2,092
Consumer Portfolio Segment | Real estate secured loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	1,518	143
Total unpaid principal of impaired loans	2,789	1,393
Consumer Portfolio Segment | Other consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	2,399	0
Total unpaid principal of impaired loans	2,399	0
Consumer Portfolio Segment | Consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	3,917	143
Total unpaid principal of impaired loans	5,188	1,393
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	1,518	143
Consumer Portfolio Segment | Impaired loans for which there is a related allowance for loan losses | Other consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	2,399	0
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	3,917	143
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 | Other consumer 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