Loans and Allowance for Loan Losses - Credit Quality Indicators, Broken out by Portfolio Segment and Class of Financing Receivables (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	$ 18,949,902	$ 16,857,131
Pass
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	17,866,637	15,926,946
Performing (Criticized)
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	909,606	747,501
Performing Impaired (Criticized)
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	49,340	59,292
Nonperforming Impaired (Nonaccrual)
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	124,319	123,392
Commercial Portfolio Segment | Software and internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	5,570,953	5,482,110
Commercial Portfolio Segment | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,131,574	1,080,231
Commercial Portfolio Segment | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	7,129,763	5,511,929
Commercial Portfolio Segment | Life science/healthcare
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,793,880	1,724,545
Commercial Portfolio Segment | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	831,108	849,395
Commercial Portfolio Segment | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	505,858	438,869
Commercial Portfolio Segment | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	16,963,136	15,087,079
Commercial Portfolio Segment | Pass | Software and internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	4,896,785	4,933,179
Commercial Portfolio Segment | Pass | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	958,512	955,675
Commercial Portfolio Segment | Pass | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	7,129,763	5,474,929
Commercial Portfolio Segment | Pass | Life science/healthcare
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,601,046	1,544,555
Commercial Portfolio Segment | Pass | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	802,929	825,058
Commercial Portfolio Segment | Pass | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	491,745	429,481
Commercial Portfolio Segment | Pass | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	15,880,780	14,162,877
Commercial Portfolio Segment | Performing (Criticized) | Software and internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	580,197	448,065
Commercial Portfolio Segment | Performing (Criticized) | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	150,311	96,820
Commercial Portfolio Segment | Performing (Criticized) | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	0	37,000
Commercial Portfolio Segment | Performing (Criticized) | Life science/healthcare
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	143,569	128,636
Commercial Portfolio Segment | Performing (Criticized) | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	26,883	22,272
Commercial Portfolio Segment | Performing (Criticized) | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	8,646	8,868
Commercial Portfolio Segment | Performing (Criticized) | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	909,606	741,661
Commercial Portfolio Segment | Performing Impaired (Criticized) | Software and internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	24,097	23,321
Commercial Portfolio Segment | Performing Impaired (Criticized) | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	22,694	27,306
Commercial Portfolio Segment | Performing Impaired (Criticized) | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	0	0
Commercial Portfolio Segment | Performing Impaired (Criticized) | Life science/healthcare
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	0	7,247
Commercial Portfolio Segment | Performing Impaired (Criticized) | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,296	898
Commercial Portfolio Segment | Performing Impaired (Criticized) | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	467	520
Commercial Portfolio Segment | Performing Impaired (Criticized) | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	48,554	59,292
Commercial Portfolio Segment | Nonperforming Impaired (Nonaccrual) | Software and internet
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	69,874	77,545
Commercial Portfolio Segment | Nonperforming Impaired (Nonaccrual) | Hardware
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	57	430
Commercial Portfolio Segment | Nonperforming Impaired (Nonaccrual) | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	0	0
Commercial Portfolio Segment | Nonperforming Impaired (Nonaccrual) | Life science/healthcare
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	49,265	44,107
Commercial Portfolio Segment | Nonperforming Impaired (Nonaccrual) | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	0	1,167
Commercial Portfolio Segment | Nonperforming Impaired (Nonaccrual) | Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	5,000	0
Commercial Portfolio Segment | Nonperforming Impaired (Nonaccrual) | Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	124,196	123,249
Consumer Portfolio Segment | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,747,144	1,543,340
Consumer Portfolio Segment | Other consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	239,622	226,712
Consumer Portfolio Segment | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,986,766	1,770,052
Consumer Portfolio Segment | Pass | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,747,021	1,539,468
Consumer Portfolio Segment | Pass | Other consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	238,836	224,601
Consumer Portfolio Segment | Pass | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	1,985,857	1,764,069
Consumer Portfolio Segment | Performing (Criticized) | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	0	3,729
Consumer Portfolio Segment | Performing (Criticized) | Other consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	0	2,111
Consumer Portfolio Segment | Performing (Criticized) | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	0	5,840
Consumer Portfolio Segment | Performing Impaired (Criticized) | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	0	0
Consumer Portfolio Segment | Performing Impaired (Criticized) | Other consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	786	0
Consumer Portfolio Segment | Performing Impaired (Criticized) | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	786	0
Consumer Portfolio Segment | Nonperforming Impaired (Nonaccrual) | Real estate secured loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	123	143
Consumer Portfolio Segment | Nonperforming Impaired (Nonaccrual) | Other consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	0	0
Consumer Portfolio Segment | Nonperforming Impaired (Nonaccrual) | Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Financing receivable	$ 123	$ 143