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 $)	Jun. 30, 2013		Dec. 31, 2012
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	$ 41,159,000		$ 38,279,000
Total unpaid principal of impaired loans (1)	69,610,000	[1]	66,242,000	[1]
Total unpaid principal of imapired loans, previously reported			55,400,000
Commercial loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	36,586,000		34,939,000
Total unpaid principal of impaired loans (1)	58,825,000	[1]	57,601,000	[1]
Commercial loans | Software
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	6,632,000		3,263,000
Total unpaid principal of impaired loans (1)	6,936,000	[1]	4,475,000	[1]
Commercial loans | Hardware
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	24,582,000		21,863,000
Total unpaid principal of impaired loans (1)	45,444,000	[1]	38,551,000	[1]
Commercial loans | Venture capital/private equity
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	89,000		0
Total unpaid principal of impaired loans (1)	89,000	[1]	0	[1]
Commercial loans | Premium wine
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	1,511,000		4,398,000
Total unpaid principal of impaired loans (1)	1,794,000	[1]	4,716,000	[1]
Commercial loans | Other
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	3,772,000		5,415,000
Total unpaid principal of impaired loans (1)	4,562,000	[1]	9,859,000	[1]
Consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	4,573,000		3,340,000
Total unpaid principal of impaired loans (1)	10,785,000	[1]	8,641,000	[1]
Consumer loans | Real estate secured loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	3,619,000		2,239,000
Total unpaid principal of impaired loans (1)	9,593,000	[1]	7,341,000	[1]
Consumer loans | Consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	954,000		1,101,000
Total unpaid principal of impaired loans (1)	1,192,000	[1]	1,300,000	[1]
Impaired loans for which there is a related allowance for loan losses
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	29,275,000		26,155,000
Impaired loans for which there is a related allowance for loan losses | Commercial loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	28,321,000		25,054,000
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	5,637,000		3,191,000
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	22,595,000		21,863,000
Impaired loans for which there is a related allowance for loan losses | Commercial loans | Venture capital/private equity
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	89,000		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	954,000		1,101,000
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	0		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	954,000		1,101,000
Impaired loans for which there is no related allowance for loan losses
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	11,884,000		12,124,000
Impaired loans for which there is no related allowance for loan losses | Commercial loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	8,265,000		9,885,000
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	995,000		72,000
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	1,987,000		0
Impaired loans for which there is no related allowance for loan losses | Commercial loans | Venture capital/private equity
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	1,511,000		4,398,000
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	3,772,000		5,415,000
Impaired loans for which there is no related allowance for loan losses | Consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	3,619,000		2,239,000
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	3,619,000		2,239,000
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

[1] The unpaid principal balances for hardware and real estate secured consumer loans as of December 31, 2012 have been corrected from previously reported amounts resulting in the total unpaid principal of impaired loans at December 31, 2012 changing from $55.4 million to $66.2 million.