Loans, Allowance for Loan Losses and Allowance for Unfunded Credit Commitments - Average Impaired Loans, Broken out by Portfolio Segment and Class of Financing Receivable (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Financing Receivable, Impaired [Line Items]
Average impaired loans	$ 191,236	$ 159,676
Interest income on impaired loans	1,196	975
Private equity/venture capital
Financing Receivable, Impaired [Line Items]
Average impaired loans	358	0
Commercial Portfolio Segment | Software/internet
Financing Receivable, Impaired [Line Items]
Average impaired loans	109,916	89,367
Interest income on impaired loans	422	421
Commercial Portfolio Segment | Hardware
Financing Receivable, Impaired [Line Items]
Average impaired loans	34,110	24,426
Interest income on impaired loans	572	397
Commercial Portfolio Segment | Private equity/venture capital
Financing Receivable, Impaired [Line Items]
Interest income on impaired loans	2	0
Commercial Portfolio Segment | Life science/healthcare
Financing Receivable, Impaired [Line Items]
Average impaired loans	38,942	39,690
Interest income on impaired loans	150	133
Commercial Portfolio Segment | Premium wine
Financing Receivable, Impaired [Line Items]
Average impaired loans	3,213	2,171
Interest income on impaired loans	38	17
Commercial Portfolio Segment | Other
Financing Receivable, Impaired [Line Items]
Average impaired loans	1,061	3,853
Interest income on impaired loans	4	7
Commercial Portfolio Segment | Commercial loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	187,600	159,507
Interest income on impaired loans	1,188	975
Consumer Portfolio Segment | Real estate secured loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	1,488	135
Interest income on impaired loans	0	0
Consumer Portfolio Segment | Other consumer loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	2,148	34
Interest income on impaired loans	8	0
Consumer Portfolio Segment | Consumer loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	3,636	169
Interest income on impaired loans	$ 8	$ 0