Investment Securities - Net Gains on Non-marketable and Other Equity Securities (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Gain (Loss) on Securities [Line Items]
Total net gains on non-marketable and other equity securities	$ 32,658	$ 9,058
Non-marketable securities
Gain (Loss) on Securities [Line Items]
Unrealized net gains on non-marketable and other equity securities still held	22,823	31,548
Less: realized net gains (losses) on sales of securities (1)	9,835	(22,490)
Non-marketable securities | Fair value accounting | Consolidated venture capital and private equity fund investments
Gain (Loss) on Securities [Line Items]
Unrealized net gains on non-marketable and other equity securities still held	3,289	11,647
Non-marketable securities | Fair value accounting | Unconsolidated venture capital and private equity fund investments
Gain (Loss) on Securities [Line Items]
Unrealized net gains on non-marketable and other equity securities still held	8,006	11,719
Non-marketable securities | Fair value accounting | Other investments
Gain (Loss) on Securities [Line Items]
Unrealized net gains on non-marketable and other equity securities still held	5,005	1,741
Non-marketable securities | Equity method accounting | Consolidated venture capital and private equity fund investments
Gain (Loss) on Securities [Line Items]
Unrealized net gains on non-marketable and other equity securities still held	2,789	9,569
Non-marketable securities | Equity method accounting | Other investments
Gain (Loss) on Securities [Line Items]
Unrealized net gains on non-marketable and other equity securities still held	1,766	(1,037)
Non-marketable securities | Equity method accounting | Debt funds
Gain (Loss) on Securities [Line Items]
Unrealized net gains on non-marketable and other equity securities still held	0	(2,299)
Other equity securities | Fair value accounting
Gain (Loss) on Securities [Line Items]
Unrealized net gains on non-marketable and other equity securities still held	$ 11,803	$ (22,282)