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	Mar. 31, 2017	Dec. 31, 2016
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	$ 202,616	$ 234,460
Total unpaid principal of impaired loans	219,909	250,692
Impaired loans for which there is a related allowance for loan losses
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	198,342	233,370
Impaired loans for which there is no related allowance for loan losses
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	4,274	1,090
Commercial Portfolio Segment | Software/internet
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	124,836	122,748
Total unpaid principal of impaired loans	132,588	129,648
Commercial Portfolio Segment | Hardware
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	29,533	65,395
Total unpaid principal of impaired loans	34,307	70,683
Commercial Portfolio Segment | Private equity/venture capital
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	346	0
Total unpaid principal of impaired loans	346	0
Commercial Portfolio Segment | Life science/healthcare
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	39,293	38,361
Total unpaid principal of impaired loans	42,478	41,130
Commercial Portfolio Segment | Premium wine
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	3,321	3,187
Total unpaid principal of impaired loans	3,321	3,187
Commercial Portfolio Segment | Other
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	1,659	867
Total unpaid principal of impaired loans	1,953	867
Commercial Portfolio Segment | Commercial loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	198,988	230,558
Total unpaid principal of impaired loans	214,993	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	123,305	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	27,531	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	346	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	38,552	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	3,321	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	1,659	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	194,714	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	1,531	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	2,002	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	741	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	4,274	1,090
Consumer Portfolio Segment | Real estate secured loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	1,480	1,504
Total unpaid principal of impaired loans	2,768	2,779
Consumer Portfolio Segment | Other consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	2,148	2,398
Total unpaid principal of impaired loans	2,148	2,398
Consumer Portfolio Segment | Consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	3,628	3,902
Total unpaid principal of impaired loans	4,916	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	1,480	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	2,148	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	3,628	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