Investment Securities - Carrying Value and Ownership Percentage of Investments (Details) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Consolidated venture capital and private equity fund investments | Fair value accounting
Investment Holdings [Line Items]
Nonmarketable securities	$ 68,214		$ 87,180
Consolidated venture capital and private equity fund investments | Fair value accounting | Strategic Investors Fund, LP
Investment Holdings [Line Items]
Nonmarketable securities	4,414		5,729
Consolidated venture capital and private equity fund investments | Fair value accounting | Capital Preferred Return Fund, LP
Investment Holdings [Line Items]
Nonmarketable securities	36,890		45,341
Consolidated venture capital and private equity fund investments | Fair value accounting | Growth Partners, LP
Investment Holdings [Line Items]
Nonmarketable securities	26,776		35,976
Consolidated venture capital and private equity fund investments | Fair value accounting | CP I, LP
Investment Holdings [Line Items]
Nonmarketable securities	134		134
Consolidated venture capital and private equity fund investments | Equity method accounting
Investment Holdings [Line Items]
Nonmarketable securities	233,996		215,367
Consolidated venture capital and private equity fund investments | Equity method accounting | Strategic Investors Fund II, LP
Investment Holdings [Line Items]
Nonmarketable securities	3,083		3,612
Consolidated venture capital and private equity fund investments | Equity method accounting | Strategic Investors Fund III, LP
Investment Holdings [Line Items]
Nonmarketable securities	14,211		15,668
Consolidated venture capital and private equity fund investments | Equity method accounting | Strategic Investors Fund IV, LP
Investment Holdings [Line Items]
Nonmarketable securities	24,743		27,064
Consolidated venture capital and private equity fund investments | Equity method accounting | Strategic Investors Fund V funds
Investment Holdings [Line Items]
Nonmarketable securities	47,734		46,830
Consolidated venture capital and private equity fund investments | Equity method accounting | CP II, LP
Investment Holdings [Line Items]
Nonmarketable securities	4,646		5,907
Consolidated venture capital and private equity fund investments | Equity method accounting | Other venture capital and private equity fund investments
Investment Holdings [Line Items]
Nonmarketable securities	139,579		116,286
Debt funds | Equity method accounting
Investment Holdings [Line Items]
Nonmarketable securities	7,004		7,271
Debt funds | Equity method accounting | Gold Hill Capital 2008, LP
Investment Holdings [Line Items]
Nonmarketable securities	5,334		5,525
Debt funds | Equity method accounting | Other debt funds
Investment Holdings [Line Items]
Nonmarketable securities	1,670		1,746
Other investments | Fair value accounting
Investment Holdings [Line Items]
Nonmarketable securities	56,206		55,255
Other investments | Equity method accounting
Investment Holdings [Line Items]
Nonmarketable securities	181,543		152,863
Other investments | Equity method accounting | SPD Silicon Valley Bank Co., Ltd.
Investment Holdings [Line Items]
Nonmarketable securities	105,863		74,190
Other investments | Equity method accounting | Other investments
Investment Holdings [Line Items]
Nonmarketable securities	$ 75,680		$ 78,673
Non-marketable securities | Consolidated venture capital and private equity fund investments | Fair value accounting | Strategic Investors Fund, LP
Investment Holdings [Line Items]
Percentage of ownership	12.60%	12.60%
Non-marketable securities | Consolidated venture capital and private equity fund investments | Fair value accounting | Capital Preferred Return Fund, LP
Investment Holdings [Line Items]
Percentage of ownership	20.00%	20.00%
Non-marketable securities | Consolidated venture capital and private equity fund investments | Fair value accounting | Growth Partners, LP
Investment Holdings [Line Items]
Percentage of ownership	33.00%	33.00%
Non-marketable securities | Consolidated venture capital and private equity fund investments | Fair value accounting | CP I, LP
Investment Holdings [Line Items]
Percentage of ownership	10.70%	10.70%
Non-marketable securities | Consolidated venture capital and private equity fund investments | Equity method accounting | Strategic Investors Fund II, LP
Investment Holdings [Line Items]
Percentage of ownership	8.60%	8.60%
Non-marketable securities | Consolidated venture capital and private equity fund investments | Equity method accounting | Strategic Investors Fund III, LP
Investment Holdings [Line Items]
Percentage of ownership	5.90%	5.90%
Non-marketable securities | Consolidated venture capital and private equity fund investments | Equity method accounting | Strategic Investors Fund IV, LP
Investment Holdings [Line Items]
Percentage of ownership	5.00%	5.00%
Non-marketable securities | Consolidated venture capital and private equity fund investments | Equity method accounting | CP II, LP
Investment Holdings [Line Items]
Percentage of ownership	5.10%	5.10%
Non-marketable securities | Consolidated venture capital and private equity fund investments | Equity method accounting | CP II, LP | Direct ownership interest
Investment Holdings [Line Items]
Percentage of ownership	1.30%
Non-marketable securities | Consolidated venture capital and private equity fund investments | Equity method accounting | CP II, LP | Indirect ownership interest
Investment Holdings [Line Items]
Percentage of ownership	3.80%
Non-marketable securities | Debt funds | Equity method accounting | Direct ownership interest
Investment Holdings [Line Items]
Percentage of ownership	11.50%
Non-marketable securities | Debt funds | Equity method accounting | Indirect ownership interest
Investment Holdings [Line Items]
Percentage of ownership	4.00%
Non-marketable securities | Debt funds | Equity method accounting | Gold Hill Capital 2008, LP
Investment Holdings [Line Items]
Percentage of ownership	15.50%	15.50%
Non-marketable securities | Other investments | Equity method accounting | SPD Silicon Valley Bank Co., Ltd.
Investment Holdings [Line Items]
Percentage of ownership	50.00%	50.00%