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, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	$ 42,382	$ 38,137
Total unpaid principal of impaired loans	46,791	42,899
Software and internet
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	34,716	33,287
Total unpaid principal of impaired loans	35,027	34,218
Hardware
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	510	2,521
Total unpaid principal of impaired loans	525	2,535
Private equity/venture capital
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	0	0
Total unpaid principal of impaired loans	0	0
Life science & healthcare
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	250	475
Total unpaid principal of impaired loans	2,453	2,453
Premium wine
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	1,270	1,304
Total unpaid principal of impaired loans	1,734	1,743
Commercial loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	42,102	37,820
Total unpaid principal of impaired loans	45,099	41,182
Other
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	5,356	233
Total unpaid principal of impaired loans	5,360	233
Real estate secured loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	210	192
Total unpaid principal of impaired loans	1,438	1,412
Consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	70	125
Total unpaid principal of impaired loans	254	305
Consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	280	317
Total unpaid principal of impaired loans	1,692	1,717
Impaired loans for which there is a related allowance for loan losses
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	40,932	35,523
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	34,716	33,287
Impaired loans for which there is a related allowance for loan losses | Hardware
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	510	1,403
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
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	250	475
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
Impaired loans for which there is a related allowance for loan losses | Commercial loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	40,832	35,398
Impaired loans for which there is a related allowance for loan losses | Other
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	5,356	233
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	30	0
Impaired loans for which there is a related allowance for loan losses | Consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	70	125
Impaired loans for which there is a related allowance for loan losses | Consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	100	125
Impaired loans for which there is no related allowance for loan losses
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	1,450	2,614
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
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
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
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
Impaired loans for which there is no related allowance for loan losses | Premium wine
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	1,270	1,304
Impaired loans for which there is no related allowance for loan losses | Commercial loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	1,270	2,422
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
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	180	192
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
Impaired loans for which there is no related allowance for loan losses | Consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	$ 180	$ 192