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		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Financing Receivable, Impaired [Line Items]
Average impaired loans	$ 101,643	$ 15,035	$ 67,991	$ 25,846
Commercial Portfolio Segment | Software and internet
Financing Receivable, Impaired [Line Items]
Average impaired loans	77,156	10,651	54,543	13,690
Commercial Portfolio Segment | Hardware
Financing Receivable, Impaired [Line Items]
Average impaired loans	2,796	1,540	1,944	8,140
Commercial Portfolio Segment | Life science & healthcare
Financing Receivable, Impaired [Line Items]
Average impaired loans	17,184	333	6,526	636
Commercial Portfolio Segment | Premium wine
Financing Receivable, Impaired [Line Items]
Average impaired loans	1,213	1,364	1,245	1,398
Commercial Portfolio Segment | Other
Financing Receivable, Impaired [Line Items]
Average impaired loans	3,132	674	3,498	1,383
Commercial Portfolio Segment | Commercial loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	101,481	14,562	67,756	25,247
Consumer Portfolio Segment | Real estate secured loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	162	212	180	224
Consumer Portfolio Segment | Other consumer loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	0	261	55	375
Consumer Portfolio Segment | Consumer loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	$ 162	$ 473	$ 235	$ 599