Investment Securities - Net Gains on Non-marketable and Other Equity Securities (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Gain (Loss) on Investments [Line Items]
Total net gains on non-marketable and other equity securities	$ 36,114	$ 17,753	$ 45,172	$ 33,115
Non-marketable securities
Gain (Loss) on Investments [Line Items]
Unrealized net gains on non-marketable and other equity securities still held	34,199	17,722	66,335	29,711
Less: Net gains (losses) on non-marketable and other equity securities sold	1,915	31	(21,163)	3,404
Non-marketable securities | Fair value accounting | Consolidated venture capital and private equity fund investments
Gain (Loss) on Investments [Line Items]
Unrealized net gains on non-marketable and other equity securities still held	4,397	9,713	16,044	16,176
Non-marketable securities | Fair value accounting | Unconsolidated venture capital and private equity fund investments
Gain (Loss) on Investments [Line Items]
Unrealized net gains on non-marketable and other equity securities still held	19,136	6,184	30,855	9,231
Non-marketable securities | Fair value accounting | Other investments
Gain (Loss) on Investments [Line Items]
Unrealized net gains on non-marketable and other equity securities still held	60	30	1,801	3,403
Non-marketable securities | Equity method accounting | Consolidated venture capital and private equity fund investments
Gain (Loss) on Investments [Line Items]
Unrealized net gains on non-marketable and other equity securities still held	9,212	2,657	18,781	6,391
Non-marketable securities | Equity method accounting | Other investments
Gain (Loss) on Investments [Line Items]
Unrealized net gains on non-marketable and other equity securities still held	2,495	(1,488)	1,458	(2,230)
Non-marketable securities | Equity method accounting | Debt funds
Gain (Loss) on Investments [Line Items]
Unrealized net gains on non-marketable and other equity securities still held	726	682	(1,573)	251
Other equity securities | Fair value accounting
Gain (Loss) on Investments [Line Items]
Unrealized net gains on non-marketable and other equity securities still held	$ 88	$ (25)	$ (22,194)	$ (107)