Investment Securities - Net Gains on Non-marketable and Other Equity Securities (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Gain (Loss) on Securities [Line Items]
Total net gains on non-marketable and other equity securities	$ 189,837	$ 29,849	$ 209,595	$ 110,480
Non-marketable securities
Gain (Loss) on Securities [Line Items]
Less: realized net gains on sales of non-marketable and other equity securities	5,262	277	5,477	12,637
Net gains on non-marketable and other equity securities still held	184,575	29,572	204,118	97,843
Non-marketable securities | Fair value accounting | Consolidated venture capital and private equity fund investments
Gain (Loss) on Securities [Line Items]
Total net gains on non-marketable and other equity securities	8,778	4,555	13,168	22,674
Non-marketable securities | Fair value accounting | Unconsolidated venture capital and private equity fund investments
Gain (Loss) on Securities [Line Items]
Total net gains on non-marketable and other equity securities	16,400	8,530	15,187	26,688
Non-marketable securities | Fair value accounting | Other investments
Gain (Loss) on Securities [Line Items]
Total net gains on non-marketable and other equity securities	217	(471)	(3,619)	4,701
Non-marketable securities | Equity method accounting | Consolidated venture capital and private equity fund investments
Gain (Loss) on Securities [Line Items]
Total net gains on non-marketable and other equity securities	51,334	29,049	69,681	54,189
Non-marketable securities | Equity method accounting | Debt funds
Gain (Loss) on Securities [Line Items]
Total net gains on non-marketable and other equity securities	15	187	(253)	1,529
Non-marketable securities | Equity method accounting | Other investments
Gain (Loss) on Securities [Line Items]
Total net gains on non-marketable and other equity securities	478	(22)	(2,668)	593
Other equity securities | Fair value accounting
Gain (Loss) on Securities [Line Items]
Total net gains on non-marketable and other equity securities	$ 112,615	$ (11,979)	$ 118,099	$ 106