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
	Mar. 31, 2019	Mar. 31, 2018
Financing Receivable, Impaired [Line Items]
Average impaired loans	$ 181,502	$ 176,777
Interest income on impaired loans	1,274	973
Private equity/venture capital
Financing Receivable, Impaired [Line Items]
Average impaired loans	5,198	302
Commercial loans | Software/internet
Financing Receivable, Impaired [Line Items]
Average impaired loans	104,312	108,788
Interest income on impaired loans	603	532
Commercial loans | Hardware
Financing Receivable, Impaired [Line Items]
Average impaired loans	16,815	38,426
Interest income on impaired loans	252	363
Commercial loans | Private equity/venture capital
Financing Receivable, Impaired [Line Items]
Interest income on impaired loans	0	0
Commercial loans | Life science/healthcare
Financing Receivable, Impaired [Line Items]
Average impaired loans	44,163	22,679
Interest income on impaired loans	347	37
Commercial loans | Premium wine
Financing Receivable, Impaired [Line Items]
Average impaired loans	1,256	2,769
Interest income on impaired loans	18	36
Commercial loans | Other
Financing Receivable, Impaired [Line Items]
Average impaired loans	140	11
Interest income on impaired loans	0	0
Commercial loans | Commercial loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	171,884	172,975
Interest income on impaired loans	1,220	968
Consumer loans | Real estate secured loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	9,613	3,063
Interest income on impaired loans	54	0
Consumer loans | Other consumer loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	5	739
Interest income on impaired loans	0	5
Consumer loans | Consumer loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	9,618	3,802
Interest income on impaired loans	$ 54	$ 5