Loans, Allowance for Loan Losses and Allowance for Unfunded Credit Commitments - Activity in Allowance for Loan Losses Broken out by Portfolio Segment (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015
Financing Receivable, Allowance for Credit Losses [Line Items]
Reserve For Unfunded Credit Commitments	$ 47,000	$ 34,889	$ 47,000	$ 34,889	$ 46,335	$ 45,265	$ 34,541	$ 34,415
Provision for unfunded credit commitments	621	413	1,676	547
Foreign Currency Translation, Unfunded Credit Commitments	44	(65)	59	(73)
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	243,130	230,249	225,366	217,613
Charge-offs	(25,081)	(20,676)	(39,111)	(46,850)
Recoveries	2,535	1,261	4,327	6,074
Provision for credit losses	15,185	36,333	44,864	69,674
Foreign Currency Translation Adjustments	727	(2,444)	1,050	(1,788)
Ending Balance	236,496	244,723	236,496	244,723
Commercial Portfolio Segment | Software/internet
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	109,502	106,898	97,388	103,045
Charge-offs	(19,401)	(18,055)	(27,381)	(40,216)
Recoveries	1,236	260	2,407	4,220
Provision for credit losses	1,527	16,215	20,246	37,847
Foreign Currency Translation Adjustments	73	(1,089)	277	(667)
Ending Balance	92,937	104,229	92,937	104,229
Commercial Portfolio Segment | Hardware
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	23,284	23,836	31,166	23,085
Charge-offs	(249)	(2,015)	(4,273)	(3,501)
Recoveries	77	183	344	422
Provision for credit losses	4,474	2,003	394	3,962
Foreign Currency Translation Adjustments	214	(136)	169	(97)
Ending Balance	27,800	23,871	27,800	23,871
Commercial Portfolio Segment | Private equity/venture capital
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	57,078	43,686	50,299	35,282
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provision for credit losses	9,263	6,562	15,969	14,805
Foreign Currency Translation Adjustments	444	(441)	517	(280)
Ending Balance	66,785	49,807	66,785	49,807
Commercial Portfolio Segment | Life science/healthcare
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	31,542	30,285	25,446	36,576
Charge-offs	(4,678)	(606)	(6,410)	(3,001)
Recoveries	8	185	44	676
Provision for credit losses	819	12,853	8,527	8,550
Foreign Currency Translation Adjustments	39	(865)	123	(949)
Ending Balance	27,730	41,852	27,730	41,852
Commercial Portfolio Segment | Premium wine
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	4,343	5,244	4,115	5,205
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provision for credit losses	(1,155)	(465)	(929)	(426)
Foreign Currency Translation Adjustments	(55)	31	(53)	31
Ending Balance	3,133	4,810	3,133	4,810
Commercial Portfolio Segment | Other
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	4,377	9,547	4,768	4,252
Charge-offs	(753)	0	(1,047)	(30)
Recoveries	180	599	477	673
Provision for credit losses	316	(714)	(74)	4,431
Foreign Currency Translation Adjustments	15	48	11	154
Ending Balance	4,135	9,480	4,135	9,480
Commercial Portfolio Segment | Commercial loans
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	230,126	219,496	213,182	207,445
Charge-offs	(25,081)	(20,676)	(39,111)	(46,748)
Recoveries	1,501	1,227	3,272	5,991
Provision for credit losses	15,244	36,454	44,133	69,169
Foreign Currency Translation Adjustments	730	(2,452)	1,044	(1,808)
Ending Balance	222,520	234,049	222,520	234,049
Consumer Portfolio Segment | Consumer loans
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	13,004	10,753	12,184	10,168
Charge-offs	0	0	0	(102)
Recoveries	1,034	34	1,055	83
Provision for credit losses	(59)	(121)	731	505
Foreign Currency Translation Adjustments	(3)	8	6	20
Ending Balance	$ 13,976	$ 10,674	$ 13,976	$ 10,674