Fair Value of Financial Instruments - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Detail) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	$ 9,593,366	$ 11,120,664
Fair Value, Derivative Assets	105,780	108,389
Fair value, Liabilities	97,204	108,581
Client interest rate derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Derivative Assets	6,422	11,753
Fair value, Liabilities	12,532	11,940
Derivatives not designated as hedging instruments | Equity warrant assets | Other assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Derivative Assets	143,725	123,763
Derivatives not designated as hedging instruments | Client interest rate derivatives | Other assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Derivative Assets	6,422	11,753
Derivatives not designated as hedging instruments | Client interest rate derivatives | Other liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value, Liabilities	$ (12,532)	$ (11,940)
Level 3 | Equity warrant asset, public portfolio | Other assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Sales restrictions discount rate	18.60%	15.50%
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	$ 9,593,366	$ 11,120,664
Total assets	10,191,403	11,481,237
Total liabilities	97,204	108,581
Fair Value, Measurements, Recurring | Derivatives not designated as hedging instruments | Foreign exchange contract | Other assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Derivative Assets	99,358	96,636
Fair Value, Measurements, Recurring | Derivatives not designated as hedging instruments | Foreign exchange contract | Other liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value, Liabilities	84,672	96,641
Fair Value, Measurements, Recurring | Derivatives not designated as hedging instruments | Equity warrant assets | Other assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Derivative Assets	143,725	123,763
Fair Value, Measurements, Recurring | Derivatives not designated as hedging instruments | Client interest rate derivatives | Other assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Derivative Assets	6,422	11,753
Fair Value, Measurements, Recurring | Derivatives not designated as hedging instruments | Client interest rate derivatives | Other liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value, Liabilities		11,940
Fair Value, Measurements, Recurring | Derivatives not designated as hedging instruments | Other derivative instruments | Other liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value, Liabilities	12,532
Fair Value, Measurements, Recurring | Fair value accounting
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	348,532	128,421
Fair Value, Measurements, Recurring | Fair value accounting | Unconsolidated venture capital and private equity fund investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	1,001	919
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		310
Fair Value, Measurements, Recurring | U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	5,733,070	6,840,502
Fair Value, Measurements, Recurring | U.S. agency debentures
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	1,485,864	1,567,128
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	2,038,134	2,267,035
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	336,298	373,730
Fair Value, Measurements, Recurring | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value		72,269
Fair Value, Measurements, Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	5,733,070	6,840,660
Total assets	5,733,905	6,840,970
Total liabilities	0	0
Fair Value, Measurements, Recurring | Level 1 | Noncontrolling Interests
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets		200
Fair Value, Measurements, Recurring | Level 1 | Derivatives not designated as hedging instruments | Foreign exchange contract | Other assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Derivative Assets	0	0
Fair Value, Measurements, Recurring | Level 1 | Derivatives not designated as hedging instruments | Foreign exchange contract | Other liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value, Liabilities	0	0
Fair Value, Measurements, Recurring | Level 1 | Derivatives not designated as hedging instruments | Equity warrant assets | Other assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Derivative Assets	0	0
Fair Value, Measurements, Recurring | Level 1 | Derivatives not designated as hedging instruments | Client interest rate derivatives | Other assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Derivative Assets	0	0
Fair Value, Measurements, Recurring | Level 1 | Derivatives not designated as hedging instruments | Client interest rate derivatives | Other liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value, Liabilities		0
Fair Value, Measurements, Recurring | Level 1 | Derivatives not designated as hedging instruments | Other derivative instruments | Other liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value, Liabilities	0
Fair Value, Measurements, Recurring | Level 1 | Fair value accounting
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	835	310
Fair Value, Measurements, Recurring | Level 1 | Fair value accounting | Unconsolidated venture capital and private equity fund investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	0
Fair Value, Measurements, Recurring | Level 1 | U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	5,733,070	6,840,502
Fair Value, Measurements, Recurring | 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 | 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 | 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 | Level 1 | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value		158
Fair Value, Measurements, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	3,860,296	4,280,004
Total assets	3,975,625	4,390,825
Total liabilities	97,204	108,581
Fair Value, Measurements, Recurring | Level 2 | Derivatives not designated as hedging instruments | Foreign exchange contract | Other assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Derivative Assets	99,358	96,636
Fair Value, Measurements, Recurring | Level 2 | Derivatives not designated as hedging instruments | Foreign exchange contract | Other liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value, Liabilities	84,672	96,641
Fair Value, Measurements, Recurring | Level 2 | Derivatives not designated as hedging instruments | Equity warrant assets | Other assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Derivative Assets	5,972	2,432
Fair Value, Measurements, Recurring | Level 2 | Derivatives not designated as hedging instruments | Client interest rate derivatives | Other assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Derivative Assets	6,422	11,753
Fair Value, Measurements, Recurring | Level 2 | Derivatives not designated as hedging instruments | Client interest rate derivatives | Other liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value, Liabilities		11,940
Fair Value, Measurements, Recurring | Level 2 | Derivatives not designated as hedging instruments | Other derivative instruments | Other liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value, Liabilities	12,532
Fair Value, Measurements, Recurring | Level 2 | Fair value accounting
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	3,577	0
Fair Value, Measurements, Recurring | Level 2 | Fair value accounting | Unconsolidated venture capital and private equity fund investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	0
Fair Value, Measurements, Recurring | Level 2 | Fair value accounting | Other securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	3,577
Fair Value, Measurements, Recurring | 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 | Level 2 | U.S. agency debentures
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	1,485,864	1,567,128
Fair Value, Measurements, Recurring | 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	2,038,134	2,267,035
Fair Value, Measurements, Recurring | 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	336,298	373,730
Fair Value, Measurements, Recurring | Level 2 | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value		72,111
Fair Value, Measurements, Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	0	0
Total assets	138,754	122,250
Total liabilities	0	0
Fair Value, Measurements, Recurring | Level 3 | Noncontrolling Interests
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	900	800
Fair Value, Measurements, Recurring | Level 3 | Derivatives not designated as hedging instruments | Foreign exchange contract | Other assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Derivative Assets	0	0
Fair Value, Measurements, Recurring | Level 3 | Derivatives not designated as hedging instruments | Foreign exchange contract | Other liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value, Liabilities	0	0
Fair Value, Measurements, Recurring | Level 3 | Derivatives not designated as hedging instruments | Equity warrant assets | Other assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Derivative Assets	137,753	121,331
Fair Value, Measurements, Recurring | Level 3 | Derivatives not designated as hedging instruments | Client interest rate derivatives | Other assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Derivative Assets	0	0
Fair Value, Measurements, Recurring | Level 3 | Derivatives not designated as hedging instruments | Client interest rate derivatives | Other liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value, Liabilities		0
Fair Value, Measurements, Recurring | Level 3 | Derivatives not designated as hedging instruments | Other derivative instruments | Other liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value, Liabilities	0
Fair Value, Measurements, Recurring | Level 3 | Fair value accounting
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	1,001	919
Fair Value, Measurements, Recurring | 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 | 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 | 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 | 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 | Level 3 | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value		0
Lower Limit | Level 3 | Equity warrant asset, public portfolio
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Sales restrictions discount rate	10.00%
Upper Limit | Level 3 | Equity warrant asset, public portfolio
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Sales restrictions discount rate	20.00%
Other securities | Fair Value, Measurements, Recurring | Level 1 | Fair value accounting
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	$ 835	310
Other securities | Fair Value, Measurements, Recurring | Level 2 | Fair value accounting
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities		0
Other securities | Fair Value, Measurements, Recurring | Level 3 | Fair value accounting
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	0	0
Unconsolidated venture capital and private equity fund investments | Fair Value, Measurements, Recurring | Level 1 | Fair value accounting
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities		0
Unconsolidated venture capital and private equity fund investments | Fair Value, Measurements, Recurring | Level 2 | Fair value accounting
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities		0
Unconsolidated venture capital and private equity fund investments | Fair Value, Measurements, Recurring | Level 3 | Fair value accounting
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	1,001	919
Consolidated venture capital and private equity fund investments | Fair Value, Measurements, Recurring | Fair value accounting
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	$ 343,119	$ 127,192