Loans, Allowance for Loan Losses and Allowance for Unfunded Credit Commitments - Average Impaired Loans, Broken out by Portfolio Segment and Class of Financing Receivable (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Financing Receivable, Impaired [Line Items]
Average impaired loans	$ 125,029	$ 193,254	$ 163,369	$ 182,398
Interest income on impaired loans	810	1,421	3,672	1,981
Private equity/venture capital
Financing Receivable, Impaired [Line Items]
Average impaired loans	0	1,233	3,019	536
Commercial loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	117,907	188,924	155,981	177,968
Interest income on impaired loans	810	1,417	3,618	1,969
Commercial loans | Software/internet
Financing Receivable, Impaired [Line Items]
Average impaired loans	59,336	118,840	88,487	112,576
Interest income on impaired loans	507	607	2,275	991
Commercial loans | Hardware
Financing Receivable, Impaired [Line Items]
Average impaired loans	10,617	27,922	14,188	34,469
Interest income on impaired loans	70	410	417	499
Commercial loans | Private equity/venture capital
Financing Receivable, Impaired [Line Items]
Interest income on impaired loans	0	0	0	0
Commercial loans | Life science/healthcare
Financing Receivable, Impaired [Line Items]
Average impaired loans	42,242	38,545	47,208	27,671
Interest income on impaired loans	192	365	785	376
Commercial loans | Premium wine
Financing Receivable, Impaired [Line Items]
Average impaired loans	2,308	2,384	1,538	2,586
Interest income on impaired loans	41	35	141	103
Commercial loans | Other
Financing Receivable, Impaired [Line Items]
Average impaired loans	3,404	0	1,541	130
Interest income on impaired loans	0	0	0	0
Consumer loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	7,122	4,330	7,388	4,430
Interest income on impaired loans	0	4	54	12
Consumer loans | Real estate secured loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	7,113	4,330	7,379	3,953
Interest income on impaired loans	0	4	54	12
Consumer loans | Other consumer loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	9	0	9	477
Interest income on impaired loans	$ 0	$ 0	$ 0	$ 0