Loans, Allowance for Loan Losses and Allowance for Unfunded Credit Commitments - Impaired Loans and Allowance for Loan Losses, Broken out by Portfolio Segment and Class of Financing Receivable (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	$ 198,293	$ 234,460
Total unpaid principal of impaired loans	236,293	250,692
Impaired loans for which there is a related allowance for loan losses
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	166,439	233,370
Impaired loans for which there is no related allowance for loan losses
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	31,854	1,090
Commercial Portfolio Segment | Software/internet
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	129,627	122,748
Total unpaid principal of impaired loans	154,587	129,648
Commercial Portfolio Segment | Hardware
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	30,020	65,395
Total unpaid principal of impaired loans	35,251	70,683
Commercial Portfolio Segment | Private equity/venture capital
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	308	0
Total unpaid principal of impaired loans	308	0
Commercial Portfolio Segment | Life science/healthcare
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	31,471	38,361
Total unpaid principal of impaired loans	38,128	41,130
Commercial Portfolio Segment | Premium wine
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	3,167	3,187
Total unpaid principal of impaired loans	3,188	3,187
Commercial Portfolio Segment | Other
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	408	867
Total unpaid principal of impaired loans	1,408	867
Commercial Portfolio Segment | Commercial loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	195,001	230,558
Total unpaid principal of impaired loans	232,870	245,515
Commercial Portfolio Segment | Impaired loans for which there is a related allowance for loan losses | Software/internet
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	98,970	121,658
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	29,396	65,395
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	308	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	30,898	38,361
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	3,167	3,187
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	408	867
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	163,147	229,468
Commercial Portfolio Segment | Impaired loans for which there is no related allowance for loan losses | Software/internet
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	30,657	1,090
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	624	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	573	0
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	0
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	31,854	1,090
Consumer Portfolio Segment | Real estate secured loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	1,328	1,504
Total unpaid principal of impaired loans	1,387	2,779
Consumer Portfolio Segment | Other consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	1,964	2,398
Total unpaid principal of impaired loans	2,036	2,398
Consumer Portfolio Segment | Consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	3,292	3,902
Total unpaid principal of impaired loans	3,423	5,177
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	1,328	1,504
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	1,964	2,398
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	3,292	3,902
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