Loans and Allowance for Loan Losses - Average Impaired Loans, Broken out by Portfolio Segment and Class of Financing Receivable (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Financing Receivable, Impaired [Line Items]
Average impaired loans	$ 62,853	$ 26,849	$ 51,164	$ 31,252
Commercial Portfolio Segment | Software and internet
Financing Receivable, Impaired [Line Items]
Average impaired loans	52,747	15,742	43,236	15,210
Commercial Portfolio Segment | Hardware
Financing Receivable, Impaired [Line Items]
Average impaired loans	1,393	6,860	1,518	11,440
Commercial Portfolio Segment | Life science & healthcare
Financing Receivable, Impaired [Line Items]
Average impaired loans	1,993	552	1,197	787
Commercial Portfolio Segment | Premium wine
Financing Receivable, Impaired [Line Items]
Average impaired loans	1,239	1,398	1,261	1,415
Commercial Portfolio Segment | Other
Financing Receivable, Impaired [Line Items]
Average impaired loans	5,222	1,699	3,681	1,738
Commercial Portfolio Segment | Commercial loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	62,594	26,251	50,893	30,590
Consumer Portfolio Segment | Real estate secured loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	183	224	189	231
Consumer Portfolio Segment | Other consumer loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	76	374	82	431
Consumer Portfolio Segment | Consumer loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	$ 259	$ 598	$ 271	$ 662