Fair Value of Financial Instruments Assets and Liabilities Measured at Fair Value on a Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	$ 16,380,748	$ 13,540,655
Derivatives designated as hedging instruments | Interest rate risks | Interest rate swaps | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	2,768	4,609
Derivatives not designated as hedging instruments | Other derivative instruments | Equity warrant assets | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	137,105	116,604
Fair value accounting
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	548	108,251
Fair value accounting | Venture capital and private equity fund investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	152,237	1,130,882
Fair value accounting | Other venture capital investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	2,040	71,204
U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	11,678,035	7,302,273
U.S. agency debentures
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	2,690,029	3,561,556
Residential mortgage-backed securities | Agency-issued collateralized mortgage obligations | Fixed rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	1,399,279	1,884,843
Residential mortgage-backed securities | Agency-issued collateralized mortgage obligations | Variable rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	607,936	784,475
Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	5,469	7,508
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	16,380,748	13,540,655
Total assets	16,710,656	15,008,982
Total liabilities	30,737	31,111
Fair Value, Measurements, Recurring | Derivatives designated as hedging instruments | Interest rate risks | Interest rate swaps | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	2,768	4,609
Fair Value, Measurements, Recurring | Derivatives not designated as hedging instruments | Currency exchange risks | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	31,237	34,231
Fair Value, Measurements, Recurring | Derivatives not designated as hedging instruments | Currency exchange risks | Other liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	26,353	28,363
Fair Value, Measurements, Recurring | Derivatives not designated as hedging instruments | Other derivative instruments | Equity warrant assets | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	137,105	116,604
Fair Value, Measurements, Recurring | Derivatives not designated as hedging instruments | Other derivative instruments | Client interest rate derivatives | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	3,973	2,546
Fair Value, Measurements, Recurring | Derivatives not designated as hedging instruments | Other derivative instruments | Client interest rate derivatives | Other liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	4,384	2,748
Fair Value, Measurements, Recurring | Fair value accounting
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	154,825	1,310,337
Fair Value, Measurements, Recurring | Fair value accounting | Venture capital and private equity fund investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	152,237	1,130,882
Fair Value, Measurements, Recurring | Fair value accounting | Other venture capital investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	2,040	71,204
Fair Value, Measurements, Recurring | Fair value accounting | Other Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	548	108,251
Fair Value, Measurements, Recurring | U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	11,678,035	7,302,273
Fair Value, Measurements, Recurring | U.S. agency debentures
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	2,690,029	3,561,556
Fair Value, Measurements, Recurring | Residential mortgage-backed securities | Agency-issued collateralized mortgage obligations | Fixed rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	1,399,279	1,884,843
Fair Value, Measurements, Recurring | Residential mortgage-backed securities | Agency-issued collateralized mortgage obligations | Variable rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	607,936	784,475
Fair Value, Measurements, Recurring | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	5,469	7,508
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	11,682,552	7,306,563
Total assets	11,683,100	7,414,814
Total liabilities	0	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Derivatives designated as hedging instruments | Interest rate risks | Interest rate swaps | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Derivatives not designated as hedging instruments | Currency exchange risks | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Derivatives not designated as hedging instruments | Currency exchange risks | Other liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Derivatives not designated as hedging instruments | Other derivative instruments | Equity warrant assets | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Derivatives not designated as hedging instruments | Other derivative instruments | Client interest rate derivatives | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Derivatives not designated as hedging instruments | Other derivative instruments | Client interest rate derivatives | Other liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair value accounting
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	548	108,251
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair value accounting | Venture capital and private equity fund investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	0	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair value accounting | Other venture capital investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	0	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair value accounting | Other Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	548	108,251
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	11,678,035	7,302,273
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. agency debentures
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	0	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Residential mortgage-backed securities | Agency-issued collateralized mortgage obligations | Fixed rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	0	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Residential mortgage-backed securities | Agency-issued collateralized mortgage obligations | Variable rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	0	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	4,517	4,290
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	4,698,196	6,234,092
Total assets	4,738,111	6,277,384
Total liabilities	30,737	31,111
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Derivatives designated as hedging instruments | Interest rate risks | Interest rate swaps | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	2,768	4,609
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Derivatives not designated as hedging instruments | Currency exchange risks | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	31,237	34,231
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Derivatives not designated as hedging instruments | Currency exchange risks | Other liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	26,353	28,363
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Derivatives not designated as hedging instruments | Other derivative instruments | Equity warrant assets | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	1,937	1,906
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Derivatives not designated as hedging instruments | Other derivative instruments | Client interest rate derivatives | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	3,973	2,546
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Derivatives not designated as hedging instruments | Other derivative instruments | Client interest rate derivatives | Other liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	4,384	2,748
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Fair value accounting
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	0	0
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Fair value accounting | Venture capital and private equity fund investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	0	0
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Fair value accounting | Other venture capital investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	0	0
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Fair value accounting | Other Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	0	0
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	0	0
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | U.S. agency debentures
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	2,690,029	3,561,556
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Residential mortgage-backed securities | Agency-issued collateralized mortgage obligations | Fixed rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	1,399,279	1,884,843
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Residential mortgage-backed securities | Agency-issued collateralized mortgage obligations | Variable rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	607,936	784,475
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	952	3,218
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	0	0
Total assets	137,208	185,902
Total liabilities	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Derivatives designated as hedging instruments | Interest rate risks | Interest rate swaps | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Derivatives not designated as hedging instruments | Currency exchange risks | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Derivatives not designated as hedging instruments | Currency exchange risks | Other liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Derivatives not designated as hedging instruments | Other derivative instruments | Equity warrant assets | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	135,168	114,698
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Derivatives not designated as hedging instruments | Other derivative instruments | Client interest rate derivatives | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Derivatives not designated as hedging instruments | Other derivative instruments | Client interest rate derivatives | Other liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Fair value accounting
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	2,040	71,204
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Fair value accounting | Venture capital and private equity fund investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Fair value accounting | Other venture capital investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	2,040	71,204
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Fair value accounting | Other Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | U.S. agency debentures
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Residential mortgage-backed securities | Agency-issued collateralized mortgage obligations | Fixed rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Residential mortgage-backed securities | Agency-issued collateralized mortgage obligations | Variable rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	$ 0	$ 0