Investment Securities - Net Gains on Non-marketable and Other Equity Securities (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Gain (Loss) on Securities [Line Items]
Total net gains on non-marketable and other equity securities	$ 47,973	$ 36,114	$ 80,631	$ 45,172
Non-marketable securities
Gain (Loss) on Securities [Line Items]
Less: realized net gains (losses) on sales of securities (1)	2,524	1,915	12,359	(21,163)
Net gains on non-marketable and other equity securities still held	45,449	34,199	68,272	66,335
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	14,830	4,397	18,119	16,044
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	10,152	19,136	18,158	30,855
Non-marketable securities | Fair value accounting | Other investments
Gain (Loss) on Securities [Line Items]
Total net gains on non-marketable and other equity securities	167	60	5,172	1,801
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	22,351	9,212	25,140	18,781
Non-marketable securities | Equity method accounting | Other investments
Gain (Loss) on Securities [Line Items]
Total net gains on non-marketable and other equity securities	(1,151)	2,495	615	1,458
Non-marketable securities | Equity method accounting | Debt funds
Gain (Loss) on Securities [Line Items]
Total net gains on non-marketable and other equity securities	1,342	726	1,342	(1,573)
Other equity securities | Fair value accounting
Gain (Loss) on Securities [Line Items]
Total net gains on non-marketable and other equity securities	$ 282	$ 88	$ 12,085	$ (22,194)