Loans and Allowance for Loan Losses - Composition of Loans, Net of Unearned Income, Broken Out by Portfolio Segment and Class of Financing Receivable (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment [Line Items]
Individually Evaluated for Impairment	$ 57,773	$ 15,051
Loans, net of unearned income	16,742,070	14,384,276
Financing Receivable, Individually Evaluated for Impairment	182,684	38,137
Collectively Evaluated for Impairment	159,840	150,308
Financing Receivable, Collectively Evaluated for Impairment	16,559,386	14,346,139
Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Individually Evaluated for Impairment	57,630	15,020
Loans, net of unearned income	14,970,747	13,105,641
Financing Receivable, Individually Evaluated for Impairment	182,541	37,820
Collectively Evaluated for Impairment	149,815	142,752
Financing Receivable, Collectively Evaluated for Impairment	14,788,206	13,067,821
Commercial loans | Software and internet
Financing Receivable, Recorded Investment [Line Items]
Individually Evaluated for Impairment	34,098	13,695
Loans, net of unearned income	5,437,915	4,954,676
Financing Receivable, Individually Evaluated for Impairment	100,866	33,287
Collectively Evaluated for Impairment	68,947	67,286
Financing Receivable, Collectively Evaluated for Impairment	5,337,049	4,921,389
Commercial loans | Hardware
Financing Receivable, Recorded Investment [Line Items]
Individually Evaluated for Impairment	3,160	1,133
Loans, net of unearned income	1,071,528	1,131,006
Financing Receivable, Individually Evaluated for Impairment	27,736	2,521
Collectively Evaluated for Impairment	19,925	24,727
Financing Receivable, Collectively Evaluated for Impairment	1,043,792	1,128,485
Commercial loans | Private equity/venture capital
Financing Receivable, Recorded Investment [Line Items]
Individually Evaluated for Impairment	0	0
Loans, net of unearned income	5,467,577	4,582,906
Financing Receivable, Individually Evaluated for Impairment	0	0
Collectively Evaluated for Impairment	35,282	27,997
Financing Receivable, Collectively Evaluated for Impairment	5,467,577	4,582,906
Commercial loans | Life science/healthcare
Financing Receivable, Recorded Investment [Line Items]
Individually Evaluated for Impairment	20,230	121
Loans, net of unearned income	1,710,642	1,289,904
Financing Receivable, Individually Evaluated for Impairment	51,354	475
Collectively Evaluated for Impairment	16,346	15,087
Financing Receivable, Collectively Evaluated for Impairment	1,659,288	1,289,429
Commercial loans | Premium wine
Financing Receivable, Recorded Investment [Line Items]
Individually Evaluated for Impairment	90	0
Loans, net of unearned income	847,295	794,321
Financing Receivable, Individually Evaluated for Impairment	2,065	1,304
Collectively Evaluated for Impairment	5,115	4,473
Financing Receivable, Collectively Evaluated for Impairment	845,230	793,017
Commercial loans | Other
Financing Receivable, Recorded Investment [Line Items]
Individually Evaluated for Impairment	52	71
Loans, net of unearned income	435,790	352,828
Financing Receivable, Individually Evaluated for Impairment	520	233
Collectively Evaluated for Impairment	4,200	3,182
Financing Receivable, Collectively Evaluated for Impairment	435,270	352,595
Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Individually Evaluated for Impairment	143	31
Financing Receivable, Individually Evaluated for Impairment	143	317
Collectively Evaluated for Impairment	10,025	7,556
Financing Receivable, Collectively Evaluated for Impairment	1,771,180	1,278,318
Consumer loans | Real estate secured consumer loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	1,544,440	1,118,115
Consumer loans | Other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	$ 226,883	$ 160,520