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 $)	Sep. 30, 2013		Dec. 31, 2012
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	$ 38,048,000		$ 38,279,000
Total unpaid principal of impaired loans (1)	65,643,000	[1]	66,242,000	[1]
Total unpaid principal of impaired loans, previously reported			55,400,000
Commercial loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	33,898,000		34,939,000
Total unpaid principal of impaired loans (1)	55,322,000	[1]	57,601,000	[1]
Consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	4,150,000		3,340,000
Total unpaid principal of impaired loans (1)	10,321,000	[1]	8,641,000	[1]
Software
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	3,041,000		3,263,000
Total unpaid principal of impaired loans (1)	4,185,000	[1]	4,475,000	[1]
Hardware
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	27,446,000		21,863,000
Total unpaid principal of impaired loans (1)	46,744,000	[1]	38,551,000	[1]
Venture capital/private equity
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	47,000		0
Total unpaid principal of impaired loans (1)	47,000	[1]	0	[1]
Premium wine
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	1,476,000		4,398,000
Total unpaid principal of impaired loans (1)	1,786,000	[1]	4,716,000	[1]
Other
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	1,888,000		5,415,000
Total unpaid principal of impaired loans (1)	2,560,000	[1]	9,859,000	[1]
Real estate secured loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	3,339,000		2,239,000
Total unpaid principal of impaired loans (1)	9,256,000	[1]	7,341,000	[1]
Consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	811,000		1,101,000
Total unpaid principal of impaired loans (1)	1,065,000	[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	30,524,000		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	29,713,000		25,054,000
Impaired loans for which there is a related allowance for loan losses | Consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	811,000		1,101,000
Impaired loans for which there is a related allowance for loan losses | Software
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	3,041,000		3,191,000
Impaired loans for which there is a related allowance for loan losses | Hardware
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	25,891,000		21,863,000
Impaired loans for which there is a related allowance for loan losses | Venture capital/private equity
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	47,000		0
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 | Other
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	734,000		0
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
Impaired loans for which there is a related allowance for loan losses | Consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	811,000		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	7,524,000		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	4,185,000		9,885,000
Impaired loans for which there is no related allowance for loan losses | Consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	3,339,000		2,239,000
Impaired loans for which there is no related allowance for loan losses | Software
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	0		72,000
Impaired loans for which there is no related allowance for loan losses | Hardware
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	1,555,000		0
Impaired loans for which there is no related allowance for loan losses | 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 | Premium wine
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	1,476,000		4,398,000
Impaired loans for which there is no related allowance for loan losses | Other
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	1,154,000		5,415,000
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	3,339,000		2,239,000
Impaired loans for which there is no related allowance for loan losses | Consumer loans
Financing Receivable, Impaired [Line Items]
Carrying value of impaired loans	$ 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.