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		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Financing Receivable, Impaired [Line Items]
Average impaired loans	$ 209,473	$ 166,151	$ 200,355	$ 162,915
Interest income on impaired loans	1,453	916	2,253	1,573
Private equity/venture capital
Financing Receivable, Impaired [Line Items]
Average impaired loans	327	0	342	0
Commercial Portfolio Segment | Software/internet
Financing Receivable, Impaired [Line Items]
Average impaired loans	136,374	101,168	123,145	95,268
Interest income on impaired loans	711	438	938	763
Commercial Portfolio Segment | Hardware
Financing Receivable, Impaired [Line Items]
Average impaired loans	29,771	23,221	31,940	23,824
Interest income on impaired loans	510	442	943	749
Commercial Portfolio Segment | Private equity/venture capital
Financing Receivable, Impaired [Line Items]
Interest income on impaired loans	3	0	5	0
Commercial Portfolio Segment | Life science/healthcare
Financing Receivable, Impaired [Line Items]
Average impaired loans	36,033	33,324	37,488	36,507
Interest income on impaired loans	191	0	291	0
Commercial Portfolio Segment | Premium wine
Financing Receivable, Impaired [Line Items]
Average impaired loans	3,221	2,040	3,217	2,106
Interest income on impaired loans	38	18	76	35
Commercial Portfolio Segment | Other
Financing Receivable, Impaired [Line Items]
Average impaired loans	708	5,485	885	4,669
Interest income on impaired loans	0	7	0	15
Commercial Portfolio Segment | Commercial loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	206,434	165,238	197,017	162,374
Interest income on impaired loans	1,453	905	2,253	1,562
Consumer Portfolio Segment | Real estate secured loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	1,360	127	1,424	131
Interest income on impaired loans	0	0	0	0
Consumer Portfolio Segment | Other consumer loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	1,679	786	1,914	410
Interest income on impaired loans	0	11	0	11
Consumer Portfolio Segment | Consumer loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	3,039	913	3,338	541
Interest income on impaired loans	$ 0	$ 11	$ 0	$ 11