Investment Securities - Components of Gains and Losses (Realized and Unrealized) on Investment Securities (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Gain (Loss) on Securities [Line Items]
Gains on non-marketable and other equity securities, net	$ 88,834	$ 69,792	$ 39,545
Less: Realized net losses on the sales and OTTI of non-marketable and other equity securities	(26,097)	(355)	(4,524)
Net gains on non-marketable and other equity securities still held	114,931	70,147	44,069
Losses on sales of securities	20,800
OTTI	5,300	4,200	4,700
Gains on sales of investments		3,800	200
Fair value accounting | Non-marketable securities | Consolidated venture capital and private equity fund investments
Gain (Loss) on Securities [Line Items]
Gains on non-marketable and other equity securities, net	20,999	27,186	5,964
Fair value accounting | Non-marketable securities | Unconsolidated venture capital and private equity fund investments
Gain (Loss) on Securities [Line Items]
Gains on non-marketable and other equity securities, net	39,075	21,377	17,816
Fair value accounting | Non-marketable securities | Other investments
Gain (Loss) on Securities [Line Items]
Gains on non-marketable and other equity securities, net	3,206	3,842	(45)
Fair value accounting | Other equity securities
Gain (Loss) on Securities [Line Items]
Gains on non-marketable and other equity securities, net	(25,483)	241	(90)
Equity method accounting | Non-marketable securities | Consolidated venture capital and private equity fund investments
Gain (Loss) on Securities [Line Items]
Gains on non-marketable and other equity securities, net	49,341	14,472	4,070
Equity method accounting | Non-marketable securities | Other investments
Gain (Loss) on Securities [Line Items]
Gains on non-marketable and other equity securities, net	1,155	(6,276)	10,882
Equity method accounting | Non-marketable securities | Debt funds
Gain (Loss) on Securities [Line Items]
Gains on non-marketable and other equity securities, net	$ 541	$ 8,950	$ 948