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		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Financing Receivable, Impaired [Line Items]
Average impaired loans	$ 183,577	$ 177,163	$ 182,540	$ 176,969
Interest income on impaired loans	1,587	596	2,862	942
Private equity/venture capital
Financing Receivable, Impaired [Line Items]
Average impaired loans	3,860	72	4,529	187
Commercial loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	178,152	172,004	175,018	172,488
Interest income on impaired loans	1,587	593	2,808	934
Commercial loans | Software/internet
Financing Receivable, Impaired [Line Items]
Average impaired loans	101,813	110,101	103,062	109,444
Interest income on impaired loans	1,232	315	1,835	562
Commercial loans | Hardware
Financing Receivable, Impaired [Line Items]
Average impaired loans	15,131	37,058	15,973	37,742
Interest income on impaired loans	95	237	347	289
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	55,219	21,790	49,691	22,234
Interest income on impaired loans	246	5	593	11
Commercial loans | Premium wine
Financing Receivable, Impaired [Line Items]
Average impaired loans	1,051	2,604	1,154	2,686
Interest income on impaired loans	14	36	33	72
Commercial loans | Other
Financing Receivable, Impaired [Line Items]
Average impaired loans	1,078	379	609	195
Interest income on impaired loans	0	0	0	0
Consumer loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	5,425	5,159	7,522	4,481
Interest income on impaired loans	0	3	54	8
Consumer loans | Real estate secured loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	5,412	4,466	7,513	3,765
Interest income on impaired loans	0	3	54	8
Consumer loans | Other consumer loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	13	693	9	716
Interest income on impaired loans	$ 0	$ 0	$ 0	$ 0