Loans, Allowance for Loan Losses and Allowance for Unfunded Credit Commitments - Impaired Loans and Allowance for Loan Losses, Broken out by Portfolio Segment and Class of Financing Receivable (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Impaired [Line Items]
Total carrying value of impaired loans	$ 170,074	$ 174,861
Total unpaid principal of impaired loans	199,908	205,295
Impaired Financing Receivables With Related Allowance
Financing Receivable, Impaired [Line Items]
Impaired loans for which there is a related allowance for loan losses	73,002	88,246
Impaired Financing Receivables With No Related Allowance
Financing Receivable, Impaired [Line Items]
Impaired loans for which there is no related allowance for loan losses	97,072	86,615
Commercial loans
Financing Receivable, Impaired [Line Items]
Total carrying value of impaired loans	165,835	172,258
Total unpaid principal of impaired loans	193,939	201,147
Commercial loans | Software and internet
Financing Receivable, Impaired [Line Items]
Impaired loans for which there is a related allowance for loan losses	49,625	49,645
Impaired loans for which there is no related allowance for loan losses	65,225	61,009
Total carrying value of impaired loans	114,850	110,654
Total unpaid principal of impaired loans	131,858	129,006
Commercial loans | Hardware
Financing Receivable, Impaired [Line Items]
Impaired loans for which there is a related allowance for loan losses	1,256	15,637
Impaired loans for which there is no related allowance for loan losses	10,250	20,713
Total carrying value of impaired loans	11,506	36,350
Total unpaid principal of impaired loans	12,159	41,721
Commercial loans | Private equity/venture capital
Financing Receivable, Impaired [Line Items]
Impaired loans for which there is a related allowance for loan losses	0	658
Impaired loans for which there is no related allowance for loan losses	3,700	0
Total carrying value of impaired loans	3,700	658
Total unpaid principal of impaired loans	3,700	984
Commercial loans | Life science/healthcare
Financing Receivable, Impaired [Line Items]
Impaired loans for which there is a related allowance for loan losses	17,791	20,521
Impaired loans for which there is no related allowance for loan losses	16,276	1,166
Total carrying value of impaired loans	34,067	21,687
Total unpaid principal of impaired loans	44,446	26,360
Commercial loans | Premium wine
Financing Receivable, Impaired [Line Items]
Impaired loans for which there is a related allowance for loan losses	0	0
Impaired loans for which there is no related allowance for loan losses	1,301	2,877
Total carrying value of impaired loans	1,301	2,877
Total unpaid principal of impaired loans	1,365	2,911
Commercial loans | Other
Financing Receivable, Impaired [Line Items]
Impaired loans for which there is a related allowance for loan losses	411	32
Impaired loans for which there is no related allowance for loan losses	0	0
Total carrying value of impaired loans	411	32
Total unpaid principal of impaired loans	411	165
Commercial loans | Impaired Financing Receivables With Related Allowance
Financing Receivable, Impaired [Line Items]
Impaired loans for which there is a related allowance for loan losses	69,083	86,493
Commercial loans | Impaired Financing Receivables With No Related Allowance
Financing Receivable, Impaired [Line Items]
Impaired loans for which there is no related allowance for loan losses	96,752	85,765
Consumer loans
Financing Receivable, Impaired [Line Items]
Total carrying value of impaired loans	4,239	2,603
Total unpaid principal of impaired loans	5,969	4,148
Consumer loans | Real estate secured consumer loans
Financing Receivable, Impaired [Line Items]
Impaired loans for which there is a related allowance for loan losses	3,919	1,331
Impaired loans for which there is no related allowance for loan losses	320	850
Total carrying value of impaired loans	4,239	2,181
Total unpaid principal of impaired loans	5,969	3,712
Consumer loans | Other Loans
Financing Receivable, Impaired [Line Items]
Impaired loans for which there is a related allowance for loan losses	0	422
Impaired loans for which there is no related allowance for loan losses	0	0
Total carrying value of impaired loans	0	422
Total unpaid principal of impaired loans	0	436
Consumer loans | Impaired Financing Receivables With Related Allowance
Financing Receivable, Impaired [Line Items]
Impaired loans for which there is a related allowance for loan losses	3,919	1,753
Consumer loans | Impaired Financing Receivables With No Related Allowance
Financing Receivable, Impaired [Line Items]
Impaired loans for which there is no related allowance for loan losses	$ 320	$ 850