Investment Securities - Components of Gains and Losses (Realized and Unrealized) on Investment Securities (Detail) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015 USD ($) Investment	Jun. 30, 2014 USD ($) Investment	Jun. 30, 2015 USD ($) Investment		Jun. 30, 2014 USD ($) Investment	Dec. 31, 2014 Investment
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	$ 27,384	$ 113,913	$ 63,259		$ 352,133
Gross losses on investment securities	(2,409)	(171,233)	(5,021)		(185,541)
(Losses) gains on investment securities, net	24,975	(57,320)	58,238	[1]	166,592
Cost method accounting | Venture capital and private equity fund investments
Gain (Loss) on Investments [Line Items]
Recognized other-than-temporary impairment (OTTI) losses	$ 200	$ 300	$ 300		$ 400
Number of other-than-temporary impaired investments | Investment	8	12	17		18
Number of investments | Investment	273	282	273		282	281
Available-for-sale Securities
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	$ 235	$ 224	$ 2,925		$ 597
Gross losses on investment securities	(94)	(16,704)	(188)		(17,017)
Non-marketable securities | Fair value accounting | Venture capital and private equity fund investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	9,199	88,003	18,021		199,439
Gross losses on investment securities	(599)	(50,558)	(1,547)		(50,659)
Non-marketable securities | Fair value accounting | Other venture capital investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	0	1,973	183		4,555
Gross losses on investment securities	0	(1,297)	(52)		(2,041)
Non-marketable securities | Fair value accounting | Other securities
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	281	13,816	9,068		130,566
Gross losses on investment securities	(120)	(101,014)	(792)		(113,787)
Non-marketable securities | Equity method accounting | Venture capital and private equity fund investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	6,624	630	14,456		1,009
Gross losses on investment securities	(409)	(116)	(437)		(116)
Non-marketable securities | Equity method accounting | Debt funds
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	183	0	1,688		3,039
Gross losses on investment securities	0	(356)	(588)		(393)
Non-marketable securities | Equity method accounting | Other investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	0	2,484	865		2,708
Gross losses on investment securities	(1,010)	(584)	(1,010)		(759)
Non-marketable securities | Cost method accounting | Venture capital and private equity fund investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	10,644	1,762	15,477		5,065
Gross losses on investment securities	(174)	(353)	(398)		(509)
Non-marketable securities | Cost method accounting | Other investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	218	5,021	576		5,155
Gross losses on investment securities	$ (3)	$ (251)	$ (9)		$ (260)

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