Investment Securities - Net Gains on Non-marketable and Other Equity Securities (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Gain (Loss) on Securities [Line Items]
Total net gains on non-marketable and other equity securities	$ 29,849	$ 32,193	$ 110,480	$ 77,365
Non-marketable securities
Gain (Loss) on Securities [Line Items]
Less: realized net gains (losses) on sales of securities (1)	277	357	12,637	(20,806)
Net gains on non-marketable and other equity securities still held	29,572	31,836	97,843	98,171
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	4,555	2,928	22,674	18,971
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	8,530	6,240	26,688	37,095
Non-marketable securities | Fair value accounting | Other investments
Gain (Loss) on Securities [Line Items]
Total net gains on non-marketable and other equity securities	(471)	2,509	4,701	4,310
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	29,049	11,341	54,189	30,122
Non-marketable securities | Equity method accounting | Debt funds
Gain (Loss) on Securities [Line Items]
Total net gains on non-marketable and other equity securities	187	1,473	1,529	(100)
Non-marketable securities | Equity method accounting | Other investments
Gain (Loss) on Securities [Line Items]
Total net gains on non-marketable and other equity securities	(22)	3,295	593	4,753
Other equity securities | Fair value accounting
Gain (Loss) on Securities [Line Items]
Total net gains on non-marketable and other equity securities	$ (11,979)	$ 4,407	$ 106	$ (17,786)