Loans and Allowance for Loan Losses - Aging of Gross Loans, Broken out by Portfolio Segment and Class of Financing Receivable (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	$ 99,600	$ 32,346
Current	18,850,302	16,824,785
Loans Past Due 90 Days or More Still Accruing Interest	412	0
Total gross loans excluding impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	79,781	24,792
Current	18,696,462	16,649,655
Loans Past Due 90 Days or More Still Accruing Interest	412	0
Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	19,819	7,554
Current	153,840	175,130
Loans Past Due 90 Days or More Still Accruing Interest	0	0
30 - 59 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	80,986	10,800
30 - 59 Days Past Due | Total gross loans excluding impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	78,011	10,467
30 - 59 Days Past Due | Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	2,975	333
60 - 89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	2,020	14,325
60 - 89 Days Past Due | Total gross loans excluding impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,358	14,325
60 - 89 Days Past Due | Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	662	0
Greater Than 90 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	16,594	7,221
Greater Than 90 Days Past Due | Total gross loans excluding impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	412	0
Greater Than 90 Days Past Due | Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	16,182	7,221
Commercial Portfolio Segment | Software and internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	17,598	10,022
Current	5,459,384	5,371,222
Loans Past Due 90 Days or More Still Accruing Interest	54	0
Commercial Portfolio Segment | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	249	1,127
Current	1,108,574	1,051,368
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Commercial Portfolio Segment | Private equity/venture capital
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	11,321	17
Current	7,118,442	5,511,912
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Commercial Portfolio Segment | Life science/healthcare
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	887	7,390
Current	1,743,728	1,665,801
Loans Past Due 90 Days or More Still Accruing Interest	358	0
Commercial Portfolio Segment | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	4,537	81
Current	825,275	847,249
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Commercial Portfolio Segment | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	98	36
Current	500,293	438,313
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Commercial Portfolio Segment | Commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	34,690	18,673
Current	16,755,696	14,885,865
Loans Past Due 90 Days or More Still Accruing Interest	412	0
Commercial Portfolio Segment | 30 - 59 Days Past Due | Software and internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	16,406	3,384
Commercial Portfolio Segment | 30 - 59 Days Past Due | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	201	1,061
Commercial Portfolio Segment | 30 - 59 Days Past Due | Private equity/venture capital
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	11,258	0
Commercial Portfolio Segment | 30 - 59 Days Past Due | Life science/healthcare
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	503	853
Commercial Portfolio Segment | 30 - 59 Days Past Due | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	4,537	16
Commercial Portfolio Segment | 30 - 59 Days Past Due | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	98	14
Commercial Portfolio Segment | 30 - 59 Days Past Due | Commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	33,003	5,328
Commercial Portfolio Segment | 60 - 89 Days Past Due | Software and internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,138	6,638
Commercial Portfolio Segment | 60 - 89 Days Past Due | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	48	66
Commercial Portfolio Segment | 60 - 89 Days Past Due | Private equity/venture capital
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	63	17
Commercial Portfolio Segment | 60 - 89 Days Past Due | Life science/healthcare
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	26	6,537
Commercial Portfolio Segment | 60 - 89 Days Past Due | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	65
Commercial Portfolio Segment | 60 - 89 Days Past Due | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	22
Commercial Portfolio Segment | 60 - 89 Days Past Due | Commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,275	13,345
Commercial Portfolio Segment | Greater Than 90 Days Past Due | Software and internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	54	0
Commercial Portfolio Segment | Greater Than 90 Days Past Due | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Commercial Portfolio Segment | Greater Than 90 Days Past Due | Private equity/venture capital
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Commercial Portfolio Segment | Greater Than 90 Days Past Due | Life science/healthcare
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	358	0
Commercial Portfolio Segment | Greater Than 90 Days Past Due | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Commercial Portfolio Segment | Greater Than 90 Days Past Due | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Commercial Portfolio Segment | Greater Than 90 Days Past Due | Commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	412	0
Consumer Portfolio Segment | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	193,745	226,369
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Consumer Portfolio Segment | Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	5,776
Current	1,747,021	1,537,421
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Consumer Portfolio Segment | Other consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	45,091	343
Consumer Portfolio Segment | Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	45,091	6,119
Current	1,940,766	1,763,790
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Consumer Portfolio Segment | 30 - 59 Days Past Due | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	45,008	228
Consumer Portfolio Segment | 30 - 59 Days Past Due | Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	4,911
Consumer Portfolio Segment | 30 - 59 Days Past Due | Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	45,008	5,139
Consumer Portfolio Segment | 60 - 89 Days Past Due | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	83	115
Consumer Portfolio Segment | 60 - 89 Days Past Due | Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	865
Consumer Portfolio Segment | 60 - 89 Days Past Due | Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	83	980
Consumer Portfolio Segment | Greater Than 90 Days Past Due | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Consumer Portfolio Segment | Greater Than 90 Days Past Due | Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Consumer Portfolio Segment | Greater Than 90 Days Past Due | Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	$ 0	$ 0