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, 2013	Dec. 31, 2012
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	$ 44,346	$ 38,279
Total unpaid principal of impaired loans	74,292	55,411
Commercial loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	38,811	34,939
Total unpaid principal of impaired loans	63,332	46,926
Commercial loans | Software
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	6,094	3,263
Total unpaid principal of impaired loans	6,196	4,475
Commercial loans | Hardware
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	22,666	21,863
Total unpaid principal of impaired loans	41,943	27,876
Commercial loans | Life science
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	454	0
Total unpaid principal of impaired loans	454	0
Commercial loans | Premium wine
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	4,303	4,398
Total unpaid principal of impaired loans	4,731	4,716
Commercial loans | Other
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	5,294	5,415
Total unpaid principal of impaired loans	10,008	9,859
Consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	5,535	3,340
Total unpaid principal of impaired loans	10,960	8,485
Consumer loans | Real estate secured loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	4,443	2,239
Total unpaid principal of impaired loans	9,650	7,185
Consumer loans | Consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	1,092	1,101
Total unpaid principal of impaired loans	1,310	1,300
Impaired loans for which there is a related allowance for loan losses
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	31,133	26,155
Impaired loans for which there is a related allowance for loan losses | Commercial loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	27,270	25,054
Impaired loans for which there is a related allowance for loan losses | Commercial loans | Software
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	6,094	3,191
Impaired loans for which there is a related allowance for loan losses | Commercial loans | Hardware
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	20,722	21,863
Impaired loans for which there is a related allowance for loan losses | Commercial loans | Life science
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	454	0
Impaired loans for which there is a related allowance for loan losses | Commercial loans | 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 | Other
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	0	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	3,863	1,101
Impaired loans for which there is a related allowance for loan losses | Consumer loans | Real estate secured loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	2,771	0
Impaired loans for which there is a related allowance for loan losses | Consumer loans | Consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	1,092	1,101
Impaired loans for which there is no related allowance for loan losses
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	13,213	12,124
Impaired loans for which there is no related allowance for loan losses | Commercial loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	11,541	9,885
Impaired loans for which there is no related allowance for loan losses | Commercial loans | Software
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	0	72
Impaired loans for which there is no related allowance for loan losses | Commercial loans | Hardware
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	1,944	0
Impaired loans for which there is no related allowance for loan losses | Commercial loans | Life science
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	0	0
Impaired loans for which there is no related allowance for loan losses | Commercial loans | Premium wine
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	4,303	4,398
Impaired loans for which there is no related allowance for loan losses | Commercial loans | Other
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	5,294	5,415
Impaired loans for which there is no related allowance for loan losses | Consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	1,672	2,239
Impaired loans for which there is no related allowance for loan losses | Consumer loans | Real estate secured loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	1,672	2,239
Impaired loans for which there is no related allowance for loan losses | Consumer loans | Consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	$ 0	$ 0