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	Sep. 30, 2019	Dec. 31, 2018
Financing Receivable, Impaired [Line Items]
Impaired loans for which there is a related allowance for loan losses	$ 100,277	$ 73,002
Impaired loans for which there is no related allowance for loan losses	42,663	97,072
Total carrying value of impaired loans	142,940	170,074
Total unpaid principal of impaired loans	193,553	199,908
Commercial loans
Financing Receivable, Impaired [Line Items]
Impaired loans for which there is a related allowance for loan losses	96,949	69,083
Impaired loans for which there is no related allowance for loan losses	38,903	96,752
Total carrying value of impaired loans	135,852	165,835
Total unpaid principal of impaired loans	182,669	193,939
Commercial loans | Software/internet
Financing Receivable, Impaired [Line Items]
Impaired loans for which there is a related allowance for loan losses	55,892	49,625
Impaired loans for which there is no related allowance for loan losses	25,588	65,225
Total carrying value of impaired loans	81,480	114,850
Total unpaid principal of impaired loans	91,126	131,858
Commercial loans | Hardware
Financing Receivable, Impaired [Line Items]
Impaired loans for which there is a related allowance for loan losses	5,441	1,256
Impaired loans for which there is no related allowance for loan losses	4,482	10,250
Total carrying value of impaired loans	9,923	11,506
Total unpaid principal of impaired loans	10,175	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
Impaired loans for which there is no related allowance for loan losses		3,700
Total carrying value of impaired loans		3,700
Total unpaid principal of impaired loans		3,700
Commercial loans | Life science/healthcare
Financing Receivable, Impaired [Line Items]
Impaired loans for which there is a related allowance for loan losses	32,634	17,791
Impaired loans for which there is no related allowance for loan losses	6,887	16,276
Total carrying value of impaired loans	39,521	34,067
Total unpaid principal of impaired loans	76,305	44,446
Commercial loans | Premium wine
Financing Receivable, Impaired [Line Items]
Impaired loans for which there is a related allowance for loan losses	393	0
Impaired loans for which there is no related allowance for loan losses	1,946	1,301
Total carrying value of impaired loans	2,339	1,301
Total unpaid principal of impaired loans	2,424	1,365
Commercial loans | Other
Financing Receivable, Impaired [Line Items]
Impaired loans for which there is a related allowance for loan losses	2,589	411
Impaired loans for which there is no related allowance for loan losses	0	0
Total carrying value of impaired loans	2,589	411
Total unpaid principal of impaired loans	2,639	411
Consumer loans
Financing Receivable, Impaired [Line Items]
Impaired loans for which there is a related allowance for loan losses	3,328	3,919
Impaired loans for which there is no related allowance for loan losses	3,760	320
Total carrying value of impaired loans	7,088	4,239
Total unpaid principal of impaired loans	10,884	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	3,315	3,919
Impaired loans for which there is no related allowance for loan losses	3,760	320
Total carrying value of impaired loans	7,075	4,239
Total unpaid principal of impaired loans	10,871	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