Fair Value of Financial Instruments - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($)	9 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	$ 12,866,857,000	$ 7,790,043,000
Fair Value, Derivative Assets	188,864,000	108,901,000
Fair Value, Derivative Liabilities	148,540,000	98,050,000
Interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Derivative Assets	40,976,000
Fair Value, Derivative Liabilities	9,286,000
Client interest rate derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Derivative Assets	25,608,000	8,499,000
Fair Value, Derivative Liabilities	37,525,000	9,491,000
Derivatives not designated as hedging instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Derivative Assets	297,001,000	258,139,000
Fair Value, Derivative Liabilities	139,254,000	98,050,000
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	149,113,000	149,238,000
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	25,608,000	8,499,000
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, Derivative Liabilities	37,525,000	9,491,000
U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	6,334,848,000	4,738,258,000
U.S. agency debentures
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	100,000,000	1,084,117,000
Foreign government debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	8,847,000	5,812,000
Residential mortgage-backed securities | Agency-issued mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	4,148,700,000
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	1,679,664,000	1,880,218,000
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		81,638,000
Agency-issued commercial mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	594,798,000
Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	12,866,857,000	7,790,043,000
Total assets	13,534,475,000	8,388,011,000
Total liabilities	148,540,000	98,050,000
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	122,280,000	100,402,000
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, Derivative Liabilities	101,729,000	88,559,000
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	149,113,000	149,238,000
Recurring | Derivatives not designated as hedging instruments | Interest rate swaps | Other assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Derivative Assets	40,976,000
Recurring | Derivatives not designated as hedging instruments | Interest rate swaps | Other liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Derivative Liabilities	9,286,000
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	25,608,000	8,499,000
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, Derivative Liabilities	37,525,000	9,491,000
Recurring | Fair value accounting
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	329,641,000	339,829,000
Recurring | Consolidated venture capital and private equity fund investments | Fair value accounting
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	134,000	1,079,000
Recurring | Other securities | Fair value accounting
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	56,081,000	20,398,000
Recurring | U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	6,334,848,000	4,738,258,000
Recurring | U.S. agency debentures
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	100,000,000	1,084,117,000
Recurring | Foreign government debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	8,847,000	5,812,000
Recurring | Residential mortgage-backed securities | Agency-issued mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	4,148,700,000
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	1,679,664,000	1,880,218,000
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		81,638,000
Recurring | Agency-issued commercial mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	594,798,000
Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	6,343,695,000	4,744,070,000
Total assets	6,346,921,000	4,745,251,000
Total liabilities	0	0
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
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, Derivative Liabilities	0	0
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
Recurring | Level 1 | Derivatives not designated as hedging instruments | Interest rate swaps | Other assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Derivative Assets	0
Recurring | Level 1 | Derivatives not designated as hedging instruments | Interest rate swaps | Other liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Derivative Liabilities	0
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
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, Derivative Liabilities	0	0
Recurring | Level 1 | Fair value accounting
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	3,226,000	1,181,000
Recurring | Level 1 | Consolidated venture capital and private equity fund investments | Fair value accounting
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	0	0
Recurring | Level 1 | Other securities | Fair value accounting
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	3,226,000	1,181,000
Recurring | Level 1 | U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	6,334,848,000	4,738,258,000
Recurring | Level 1 | U.S. agency debentures
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	0	0
Recurring | Level 1 | Foreign government debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	8,847,000	5,812,000
Recurring | Level 1 | Residential mortgage-backed securities | Agency-issued mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	0
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
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
Recurring | Level 1 | Agency-issued commercial mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	0
Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	6,523,162,000	3,045,973,000
Total assets	6,768,953,000	3,178,130,000
Total liabilities	148,540,000	98,050,000
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	122,280,000	100,402,000
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, Derivative Liabilities	101,729,000	88,559,000
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	4,072,000	4,039,000
Recurring | Level 2 | Derivatives not designated as hedging instruments | Interest rate swaps | Other assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Derivative Assets	40,976,000
Recurring | Level 2 | Derivatives not designated as hedging instruments | Interest rate swaps | Other liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Derivative Liabilities	9,286,000
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	25,608,000	8,499,000
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, Derivative Liabilities	37,525,000	9,491,000
Recurring | Level 2 | Fair value accounting
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	52,855,000	19,217,000
Recurring | Level 2 | Consolidated venture capital and private equity fund investments | Fair value accounting
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	0	0
Recurring | Level 2 | Other securities | Fair value accounting
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	52,855,000	19,217,000
Recurring | Level 2 | U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	0	0
Recurring | Level 2 | U.S. agency debentures
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	100,000,000	1,084,117,000
Recurring | Level 2 | Foreign government debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	0	0
Recurring | Level 2 | Residential mortgage-backed securities | Agency-issued mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	4,148,700,000
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	1,679,664,000	1,880,218,000
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		81,638,000
Recurring | Level 2 | Agency-issued commercial mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	594,798,000
Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	0	0
Total assets	145,175,000	146,278,000
Total liabilities	0	0
Recurring | Level 3 | Noncontrolling Interests
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	120,000	964,000
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
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, Derivative Liabilities	0	0
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	145,041,000	145,199,000
Recurring | Level 3 | Derivatives not designated as hedging instruments | Interest rate swaps | Other assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Derivative Assets	0
Recurring | Level 3 | Derivatives not designated as hedging instruments | Interest rate swaps | Other liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Derivative Liabilities	0
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
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, Derivative Liabilities	0	0
Recurring | Level 3 | Fair value accounting
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	134,000	1,079,000
Recurring | Level 3 | Consolidated venture capital and private equity fund investments | Fair value accounting
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	134,000	1,079,000
Recurring | Level 3 | Other securities | Fair value accounting
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	0	0
Recurring | Level 3 | U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	0	0
Recurring | Level 3 | U.S. agency debentures
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	0	0
Recurring | Level 3 | Foreign government debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	0	0
Recurring | Level 3 | Residential mortgage-backed securities | Agency-issued mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	0
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
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
Recurring | Level 3 | Agency-issued commercial mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	0
Recurring | Measured at net asset value | Consolidated venture capital and private equity fund investments | Fair value accounting
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable securities	$ 273,426,000	$ 318,352,000
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%