Investment Securities - Components of Gains and Losses (Realized and Unrealized) on Investment Securities (Detail) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016 USD ($) Investment	Jun. 30, 2015 USD ($) Investment	Jun. 30, 2016 USD ($) Investment	Jun. 30, 2015 USD ($) Investment	Dec. 31, 2015 Investment
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	$ 31,035	$ 27,514	$ 41,424	$ 63,388
Gross losses on investment securities	(7,765)	(2,539)	(22,838)	(5,150)
Gains on investment securities, net	23,270	24,975	18,586	58,238
Cost method accounting | Venture capital and private equity fund investments
Gain (Loss) on Investments [Line Items]
Recognized other-than-temporary impairment (OTTI) losses	$ 300	$ 200	$ 400	$ 300
Number of other-than-temporary impaired investments | Investment	10	8	18	17
Number of investments | Investment	264	273	264	273	267
Available-for-sale Securities
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	$ 12,401	$ 235	$ 14,154	$ 2,925
Gross losses on investment securities	(73)	(94)	(2,572)	(188)
Non-marketable securities | Fair value accounting | Venture capital and private equity fund investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	7,524	9,199	10,347	18,021
Gross losses on investment securities	(5,943)	(599)	(13,836)	(1,547)
Non-marketable securities | Fair value accounting | Other venture capital investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	5	0	13	183
Gross losses on investment securities	0	0	(38)	(52)
Non-marketable securities | Fair value accounting | Other securities
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	305	281	368	9,068
Gross losses on investment securities	(250)	(120)	(407)	(792)
Non-marketable securities | Equity method accounting | Venture capital and private equity fund investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	2,019	6,709	3,672	12,723
Gross losses on investment securities	(466)	(409)	(4,021)	(437)
Non-marketable securities | Equity method accounting | Debt funds
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	64	183	964	1,688
Gross losses on investment securities	(284)	0	(329)	(588)
Non-marketable securities | Equity method accounting | Other investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	3,190	45	4,041	2,727
Gross losses on investment securities	(312)	(1,140)	(956)	(1,140)
Non-marketable securities | Cost method accounting | Venture capital and private equity fund investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	5,514	10,644	7,852	15,477
Gross losses on investment securities	(270)	(174)	(441)	(398)
Non-marketable securities | Cost method accounting | Other investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	13	218	13	576
Gross losses on investment securities	$ (167)	$ (3)	$ (238)	$ (8)