Loans and Allowance for Loan Losses - Activity in Allowance for Loan Losses Broken out by Portfolio Segment (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	$ 225,366	$ 217,613	$ 165,359
Charge-offs	(66,682)	(96,857)	(50,968)
Recoveries	8,538	12,212	6,209
Provision for loan losses	85,939	95,697	97,629
Allowance for Loan and Lease Losses, Foreign Currency Translation	1,863	(3,299)	(616)
Ending Balance	255,024	225,366	217,613
Software and internet
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance		103,045	80,981
Charge-offs			(33,246)
Recoveries			1,621
Provision for loan losses			53,696
Ending Balance			103,045
Hardware
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance		23,085	25,860
Charge-offs			(5,145)
Recoveries			3,332
Provision for loan losses			(1,035)
Ending Balance			23,085
Private equity/venture capital
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance		35,282	27,997
Charge-offs			0
Recoveries			0
Provision for loan losses			7,391
Ending Balance			35,282
Life science/healthcare
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance		36,576	15,208
Charge-offs			(7,291)
Recoveries			277
Provision for loan losses			28,400
Ending Balance			36,576
Premium wine
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance		5,205	4,473
Charge-offs			0
Recoveries			7
Provision for loan losses			725
Ending Balance			5,205
Other
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance		4,252	3,253
Charge-offs			(4,990)
Recoveries			809
Provision for loan losses			5,736
Ending Balance			4,252
Commercial loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	213,182	207,445	157,772
Charge-offs	(65,115)	(96,755)	(50,672)
Recoveries	7,175	11,954	6,046
Provision for loan losses	81,553	93,885	94,913
Ending Balance	238,583	213,182	207,445
Commercial loans \| Software and internet
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	97,388	103,045
Charge-offs	(45,012)	(68,784)
Allowance for Loan and Lease Loss, Recovery of Bad Debts	4,649	7,278
Provision for loan losses	38,462	58,350
Allowance for Loan and Lease Losses, Foreign Currency Translation	617	(2,501)	(7)
Ending Balance	96,104	97,388	103,045
Commercial loans \| Hardware
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	31,166	23,085
Charge-offs	(10,414)	(13,233)
Allowance for Loan and Lease Loss, Recovery of Bad Debts	487	1,667
Provision for loan losses	6,051	20,851
Allowance for Loan and Lease Losses, Foreign Currency Translation	324	(1,204)	73
Ending Balance	27,614	31,166	23,085
Commercial loans \| Private equity/venture capital
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	50,299	35,282
Charge-offs	(323)	0
Allowance for Loan and Lease Loss, Recovery of Bad Debts	0	0
Provision for loan losses	31,625	15,114
Allowance for Loan and Lease Losses, Foreign Currency Translation	867	(97)	(106)
Ending Balance	82,468	50,299	35,282
Commercial loans \| Life science/healthcare
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	25,446	36,576
Charge-offs	(8,210)	(9,693)
Allowance for Loan and Lease Loss, Recovery of Bad Debts	189	1,129
Provision for loan losses	7,414	(2,543)
Allowance for Loan and Lease Losses, Foreign Currency Translation	85	(23)	(18)
Ending Balance	24,924	25,446	36,576
Commercial loans \| Premium wine
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	4,115	5,205
Charge-offs	0	0
Allowance for Loan and Lease Loss, Recovery of Bad Debts	0	0
Provision for loan losses	(540)	(1,260)
Allowance for Loan and Lease Losses, Foreign Currency Translation	(43)	170	0
Ending Balance	3,532	4,115	5,205
Commercial loans \| Other
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	4,768	4,252
Charge-offs	(1,156)	(5,045)
Allowance for Loan and Lease Loss, Recovery of Bad Debts	1,850	1,880
Provision for loan losses	(1,459)	3,373
Allowance for Loan and Lease Losses, Foreign Currency Translation	(62)	308	(556)
Ending Balance	3,941	4,768	4,252
Commercial loans \| Commercial Loan [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan and Lease Losses, Foreign Currency Translation	1,788	(3,347)	(614)
Consumer loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	12,184	10,168	7,587
Charge-offs			(296)
Recoveries			163
Provision for loan losses			2,716
Ending Balance	16,441	12,184	10,168
Consumer loans \| Consumer Loan
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	12,184	10,168
Charge-offs	(1,567)	(102)
Allowance for Loan and Lease Loss, Recovery of Bad Debts	1,363	258
Provision for loan losses	4,386	1,812
Allowance for Loan and Lease Losses, Foreign Currency Translation	$ 75	48	(2)
Ending Balance		$ 12,184	$ 10,168

Allowance for Loan and Lease Losses, Loan Recoveries

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Amount of recovery of loans and lease receivables which had previously been fully or partially written-off as bad debts.

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Amount of gain (loss) from converting allowance reserve for credit loss to currency of reporting entity from amount denominated or measured in a different currency, which decreases (increases) the allowance for loan and lease losses.

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Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

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Amount of expense related to loss from loan transactions.

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