Loans and Allowance for Loan Losses - Allowance for Loan Losses Individually and Collectively Evaluated for Impairment (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment	$ 41,793	$ 48,825
Financing Receivable, Individually Evaluated for Impairment	174,861	234,460
Collectively Evaluated for Impairment	213,231	176,541
Financing Receivable, Collectively Evaluated for Impairment	22,931,455	19,665,484
Commercial loans
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment	41,215	47,702
Financing Receivable, Individually Evaluated for Impairment	172,258	230,558
Collectively Evaluated for Impairment	197,368	165,480
Financing Receivable, Collectively Evaluated for Impairment	20,304,572	17,501,054
Commercial loans | Software and internet
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment	23,088	28,245
Financing Receivable, Individually Evaluated for Impairment	110,654	122,748
Collectively Evaluated for Impairment	73,016	69,143
Financing Receivable, Collectively Evaluated for Impairment	6,061,877	5,504,283
Commercial loans | Hardware
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment	8,450	9,995
Financing Receivable, Individually Evaluated for Impairment	36,350	65,395
Collectively Evaluated for Impairment	19,164	21,171
Financing Receivable, Collectively Evaluated for Impairment	1,157,249	1,115,003
Commercial loans | Private equity/venture capital
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment	330	0
Financing Receivable, Individually Evaluated for Impairment	658	0
Collectively Evaluated for Impairment	82,138	50,299
Financing Receivable, Collectively Evaluated for Impairment	9,951,719	7,691,148
Commercial loans | Life science/healthcare
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment	9,315	8,709
Financing Receivable, Individually Evaluated for Impairment	21,687	38,361
Collectively Evaluated for Impairment	15,609	16,737
Financing Receivable, Collectively Evaluated for Impairment	1,787,140	1,814,643
Commercial loans | Premium wine
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment	0	520
Financing Receivable, Individually Evaluated for Impairment	2,877	3,187
Collectively Evaluated for Impairment	3,532	3,595
Financing Receivable, Collectively Evaluated for Impairment	870,281	875,135
Commercial loans | Other
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment	32	233
Financing Receivable, Individually Evaluated for Impairment	32	867
Collectively Evaluated for Impairment	3,909	4,535
Financing Receivable, Collectively Evaluated for Impairment	476,306	500,842
Consumer loans | Consumer Loan
Financing Receivable, Impaired [Line Items]
Individually Evaluated for Impairment	578	1,123
Financing Receivable, Individually Evaluated for Impairment	2,603	3,902
Collectively Evaluated for Impairment	15,863	11,061
Financing Receivable, Collectively Evaluated for Impairment	$ 2,626,883	$ 2,164,430