Fair Value of Financial Instruments - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	$ 12,603,337	$ 12,620,411
Interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value, Assets		810
Client interest rate derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value, Assets	11,824	10,110
Fair value, Liabilities	11,955	9,770
Derivatives designated as hedging instruments | Interest rate risks | Other assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value, Assets		810
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, Assets	3,166	3,057
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	1,244	968
Fair value accounting
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	392	753
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	128,768	141,649
Fair value accounting | Other venture capital investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	1,897	2,040
U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	7,498,340	8,909,491
U.S. agency debentures
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	1,676,169	2,078,375
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	3,012,695	1,152,665
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	395,880	474,283
Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	$ 20,253	$ 5,597
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	19.90%	17.70%
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	$ 12,603,337	$ 12,620,411
Total assets	12,982,950	12,974,923
Total liabilities	100,916	64,438
Fair Value, Measurements, Recurring | Derivatives designated as hedging instruments | Interest rate risks | Other assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value, Assets		810
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, Assets	94,947	68,027
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	88,961	54,668
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, Assets	141,785	131,123
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, Assets	11,824	10,110
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		9,770
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	11,955
Fair Value, Measurements, Recurring | Fair value accounting
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	131,057	144,442
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	128,768	141,649
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	1,897	2,040
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	392	753
Fair Value, Measurements, Recurring | U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	7,498,340	8,909,491
Fair Value, Measurements, Recurring | U.S. agency debentures
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	1,676,169	2,078,375
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	3,012,695	1,152,665
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	395,880	474,283
Fair Value, Measurements, Recurring | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	20,253	5,597
Fair Value, Measurements, Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	7,499,142	8,909,666
Total assets	7,499,534	8,910,419
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	300	600
Fair Value, Measurements, Recurring | Level 1 | Derivatives designated as hedging instruments | Interest rate swaps | Other assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value, Assets		0
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, 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, 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, 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	392	753
Fair Value, Measurements, Recurring | 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 | Level 1 | Fair value accounting | Other securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	392	753
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	7,498,340	8,909,491
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	802	175
Fair Value, Measurements, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	5,104,195	3,710,745
Total assets	5,213,676	3,792,002
Total liabilities	100,916	64,438
Fair Value, Measurements, Recurring | Level 2 | Derivatives designated as hedging instruments | Interest rate swaps | Other assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value, Assets		810
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, Assets	94,947	68,027
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	88,961	54,668
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, Assets	2,710	2,310
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, Assets	11,824	10,110
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		9,770
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	11,955
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	0
Fair Value, Measurements, Recurring | 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 | 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 | 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	1,676,169	2,078,375
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	3,012,695	1,152,665
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	395,880	474,283
Fair Value, Measurements, Recurring | Level 2 | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	19,451	5,422
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	140,972	130,853
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	1,700	1,800
Fair Value, Measurements, Recurring | Level 3 | Derivatives designated as hedging instruments | Interest rate swaps | Other assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value, Assets		0
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, 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, Assets	139,075	128,813
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, 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	1,897	2,040
Fair Value, Measurements, Recurring | 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	1,897	2,040
Fair Value, Measurements, Recurring | 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 | 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	$ 0
Lower Limit | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Sales restrictions discount rate	10.00%
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
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Sales restrictions discount rate	20.00%
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%