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	Jun. 30, 2019	Dec. 31, 2018
Financing Receivable, Impaired [Line Items]
Impaired loans for which there is a related allowance for loan losses	$ 92,828	$ 73,002
Impaired loans for which there is no related allowance for loan losses	92,695	97,072
Total carrying value of impaired loans	185,523	170,074
Total unpaid principal of impaired loans	222,096	199,908
Commercial loans
Financing Receivable, Impaired [Line Items]
Impaired loans for which there is a related allowance for loan losses	90,997	69,083
Impaired loans for which there is no related allowance for loan losses	88,883	96,752
Total carrying value of impaired loans	179,880	165,835
Total unpaid principal of impaired loans	212,735	193,939
Commercial loans | Software/internet
Financing Receivable, Impaired [Line Items]
Impaired loans for which there is a related allowance for loan losses	37,016	49,625
Impaired loans for which there is no related allowance for loan losses	72,060	65,225
Total carrying value of impaired loans	109,076	114,850
Total unpaid principal of impaired loans	114,285	131,858
Commercial loans | Hardware
Financing Receivable, Impaired [Line Items]
Impaired loans for which there is a related allowance for loan losses	8,868	1,256
Impaired loans for which there is no related allowance for loan losses	6,667	10,250
Total carrying value of impaired loans	15,535	11,506
Total unpaid principal of impaired loans	15,641	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	0	0
Impaired loans for which there is no related allowance for loan losses	0	3,700
Total carrying value of impaired loans	0	3,700
Total unpaid principal of impaired loans	0	3,700
Commercial loans | Life science/healthcare
Financing Receivable, Impaired [Line Items]
Impaired loans for which there is a related allowance for loan losses	41,639	17,791
Impaired loans for which there is no related allowance for loan losses	9,372	16,276
Total carrying value of impaired loans	51,011	34,067
Total unpaid principal of impaired loans	78,471	44,446
Commercial loans | Premium wine
Financing Receivable, Impaired [Line Items]
Impaired loans for which there is a related allowance for loan losses	244	0
Impaired loans for which there is no related allowance for loan losses	784	1,301
Total carrying value of impaired loans	1,028	1,301
Total unpaid principal of impaired loans	1,108	1,365
Commercial loans | Other
Financing Receivable, Impaired [Line Items]
Impaired loans for which there is a related allowance for loan losses	3,230	411
Impaired loans for which there is no related allowance for loan losses	0	0
Total carrying value of impaired loans	3,230	411
Total unpaid principal of impaired loans	3,230	411
Consumer loans
Financing Receivable, Impaired [Line Items]
Impaired loans for which there is a related allowance for loan losses	1,831	3,919
Impaired loans for which there is no related allowance for loan losses	3,812	320
Total carrying value of impaired loans	5,643	4,239
Total unpaid principal of impaired loans	9,361	5,969
Consumer loans | Real estate secured loans
Financing Receivable, Impaired [Line Items]
Impaired loans for which there is a related allowance for loan losses	1,818	3,919
Impaired loans for which there is no related allowance for loan losses	3,812	320
Total carrying value of impaired loans	5,630	4,239
Total unpaid principal of impaired loans	9,348	5,969
Consumer loans | Other consumer loans
Financing Receivable, Impaired [Line Items]
Impaired loans for which there is a related allowance for loan losses	13	0
Impaired loans for which there is no related allowance for loan losses	0	0
Total carrying value of impaired loans	13	0
Total unpaid principal of impaired loans	$ 13	$ 0