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	Jun. 30, 2015	Dec. 31, 2014
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	$ 100,802	$ 38,137
Total unpaid principal of impaired loans	103,273	42,899
Impaired loans for which there is a related allowance for loan losses
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	99,394	35,523
Impaired loans for which there is no related allowance for loan losses
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	1,408	2,614
Commercial Portfolio Segment | Software and internet
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	89,471	33,287
Total unpaid principal of impaired loans	89,877	34,218
Commercial Portfolio Segment | Hardware
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	2,357	2,521
Total unpaid principal of impaired loans	2,385	2,535
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	2,433	475
Total unpaid principal of impaired loans	2,433	2,453
Commercial Portfolio Segment | Premium wine
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	1,236	1,304
Total unpaid principal of impaired loans	1,725	1,743
Commercial Portfolio Segment | Commercial loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	100,563	37,820
Total unpaid principal of impaired loans	101,615	41,182
Commercial Portfolio Segment | Other
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	5,066	233
Total unpaid principal of impaired loans	5,195	233
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	89,471	33,287
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	2,357	1,403
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	2,433	475
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	0	0
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	99,327	35,398
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	5,066	233
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	0	1,118
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	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	1,236	1,304
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	1,236	2,422
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 | Real estate secured loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	172	192
Total unpaid principal of impaired loans	1,404	1,412
Consumer Portfolio Segment | Other consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	67	125
Total unpaid principal of impaired loans	254	305
Consumer Portfolio Segment | Consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	239	317
Total unpaid principal of impaired loans	1,658	1,717
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	0	0
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	67	125
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	67	125
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	172	192
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	$ 172	$ 192