Investment Securities - Components of Gains and Losses (Realized and Unrealized) on Investment Securities (Detail) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($) Investment	Jun. 30, 2016 USD ($) Investment	Jun. 30, 2017 USD ($) Investment	Jun. 30, 2016 USD ($) Investment	Dec. 31, 2016 Investment
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities:	$ 24,335	$ 31,035	$ 43,873	$ 41,424
Gross losses on investment securities	(6,705)	(7,765)	(10,273)	(22,838)
Gains on investment securities, net	17,630	23,270	33,600	18,586
Cost method accounting | Venture capital and private equity fund investments
Gain (Loss) on Investments [Line Items]
Recognized other-than-temporary impairment (OTTI) losses	$ 500	$ 300	$ 600	$ 400
Number of other-than-temporary impaired investments | Investment	8	10	13	18
Number of investments | Investment	244	264	244	264	252
Available-for-sale Securities
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities:	$ 418	$ 12,401	$ 1,093	$ 14,154
Gross losses on investment securities	(541)	(73)	(608)	(2,572)
Non-marketable securities | Fair value accounting | Venture capital and private equity fund investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities:	12,398	7,524	19,480	10,347
Gross losses on investment securities	(2,685)	(5,943)	(3,304)	(13,836)
Non-marketable securities | Fair value accounting | Other venture capital investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities:	0	5	0	13
Gross losses on investment securities	(143)	0	(143)	(38)
Non-marketable securities | Fair value accounting | Other securities
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities:	116	305	272	368
Gross losses on investment securities	(141)	(250)	(379)	(407)
Non-marketable securities | Equity method accounting | Venture capital and private equity fund investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities:	2,786	2,019	6,703	3,672
Gross losses on investment securities	(129)	(466)	(312)	(4,021)
Non-marketable securities | Equity method accounting | Debt funds
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities:	928	64	1,166	964
Gross losses on investment securities	(246)	(284)	(915)	(329)
Non-marketable securities | Equity method accounting | Other investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities:	779	3,190	1,521	4,041
Gross losses on investment securities	(2,267)	(312)	(3,751)	(956)
Non-marketable securities | Cost method accounting | Venture capital and private equity fund investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities:	6,870	5,514	10,029	7,852
Gross losses on investment securities	(543)	(270)	(655)	(441)
Non-marketable securities | Cost method accounting | Other investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities:	40	13	3,609	13
Gross losses on investment securities	$ (10)	$ (167)	$ (206)	$ (238)