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	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Impaired [Line Items]
Impaired loans for which there is a related allowance for loan losses	$ 110,998	$ 73,002
Impaired loans for which there is no related allowance for loan losses	90,109	97,072
Total carrying value of impaired loans	201,107	170,074
Total unpaid principal of impaired loans	233,437	199,908
Commercial loans | Software/internet
Financing Receivable, Impaired [Line Items]
Impaired loans for which there is a related allowance for loan losses	45,908	49,625
Impaired loans for which there is no related allowance for loan losses	53,026	65,225
Total carrying value of impaired loans	98,934	114,850
Total unpaid principal of impaired loans	117,640	131,858
Commercial loans | Hardware
Financing Receivable, Impaired [Line Items]
Impaired loans for which there is a related allowance for loan losses	8,054	1,256
Impaired loans for which there is no related allowance for loan losses	11,753	10,250
Total carrying value of impaired loans	19,807	11,506
Total unpaid principal of impaired loans	20,482	12,159
Commercial loans | Private equity/venture capital
Financing Receivable, Impaired [Line Items]
Impaired loans for which there is a related allowance for loan losses	2,247	0
Impaired loans for which there is no related allowance for loan losses	3,700	3,700
Total carrying value of impaired loans	5,947	3,700
Total unpaid principal of impaired loans	5,947	3,700
Commercial loans | Life science/healthcare
Financing Receivable, Impaired [Line Items]
Impaired loans for which there is a related allowance for loan losses	52,944	17,791
Impaired loans for which there is no related allowance for loan losses	14,427	16,276
Total carrying value of impaired loans	67,371	34,067
Total unpaid principal of impaired loans	78,353	44,446
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	1,236	1,301
Total carrying value of impaired loans	1,236	1,301
Total unpaid principal of impaired loans	1,305	1,365
Commercial loans | Other
Financing Receivable, Impaired [Line Items]
Impaired loans for which there is a related allowance for loan losses	4	411
Impaired loans for which there is no related allowance for loan losses	0	0
Total carrying value of impaired loans	4	411
Total unpaid principal of impaired loans	4	411
Commercial loans | Commercial loans
Financing Receivable, Impaired [Line Items]
Impaired loans for which there is a related allowance for loan losses	109,157	69,083
Impaired loans for which there is no related allowance for loan losses	84,142	96,752
Total carrying value of impaired loans	193,299	165,835
Total unpaid principal of impaired loans	223,731	193,939
Consumer loans | Real estate secured loans
Financing Receivable, Impaired [Line Items]
Impaired loans for which there is a related allowance for loan losses	1,827	3,919
Impaired loans for which there is no related allowance for loan losses	5,967	320
Total carrying value of impaired loans	7,794	4,239
Total unpaid principal of impaired loans	9,691	5,969
Consumer loans | Other consumer loans
Financing Receivable, Impaired [Line Items]
Impaired loans for which there is a related allowance for loan losses	14	0
Impaired loans for which there is no related allowance for loan losses	0	0
Total carrying value of impaired loans	14	0
Total unpaid principal of impaired loans	15	0
Consumer loans | Consumer loans
Financing Receivable, Impaired [Line Items]
Impaired loans for which there is a related allowance for loan losses	1,841	3,919
Impaired loans for which there is no related allowance for loan losses	5,967	320
Total carrying value of impaired loans	7,808	4,239
Total unpaid principal of impaired loans	$ 9,706	$ 5,969