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	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Impaired [Line Items]
Average impaired loans	$ 179,666	$ 193,120	$ 176,412
Impaired Financing Receivable, with Related Allowance, Interest Income, Accrual Method	2,664	3,566	3,884
Private equity/venture capital
Financing Receivable, Impaired [Line Items]
Average impaired loans		556
Commercial loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	175,280	189,802	174,688
Impaired Financing Receivable, with Related Allowance, Interest Income, Accrual Method	2,649	3,566	3,867
Commercial loans | Software and internet
Financing Receivable, Impaired [Line Items]
Average impaired loans	112,493	119,557	89,462
Impaired Financing Receivable, with Related Allowance, Interest Income, Accrual Method	1,513	2,263	1,054
Commercial loans | Hardware
Financing Receivable, Impaired [Line Items]
Average impaired loans	28,540	35,022	39,108
Impaired Financing Receivable, with Related Allowance, Interest Income, Accrual Method	312	1,061	2,624
Commercial loans | Private equity/venture capital
Financing Receivable, Impaired [Line Items]
Average impaired loans	1,327		0
Impaired Financing Receivable, with Related Allowance, Interest Income, Accrual Method	0	0	0
Commercial loans | Life science/healthcare
Financing Receivable, Impaired [Line Items]
Average impaired loans	30,144	30,842	40,620
Impaired Financing Receivable, with Related Allowance, Interest Income, Accrual Method	756	90	155
Commercial loans | Premium wine
Financing Receivable, Impaired [Line Items]
Average impaired loans	2,605	3,249	2,056
Impaired Financing Receivable, with Related Allowance, Interest Income, Accrual Method	68	152	28
Commercial loans | Other
Financing Receivable, Impaired [Line Items]
Average impaired loans	171	576	3,442
Impaired Financing Receivable, with Related Allowance, Interest Income, Accrual Method	0	0	6
Consumer loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	4,386	3,318	1,724
Impaired Financing Receivable, with Related Allowance, Interest Income, Accrual Method	15	0	17
Consumer loans | Real estate secured consumer loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	4,028	1,514	588
Impaired Financing Receivable, with Related Allowance, Interest Income, Accrual Method	15	0	0
Consumer loans | Other Loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	358	1,804	1,136
Impaired Financing Receivable, with Related Allowance, Interest Income, Accrual Method	$ 0	$ 0	$ 17