Investment Securities - Components of Gains and Losses (Realized and Unrealized) on Investment Securities (Detail) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015 USD ($) Investment	Sep. 30, 2014 USD ($) Investment	Sep. 30, 2015 USD ($) Investment		Sep. 30, 2014 USD ($) Investment	Dec. 31, 2014 Investment	Sep. 30, 2014 Investment
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	$ 21,787	$ 86,211	$ 85,046		$ 438,344
Gross losses on investment securities	(3,019)	(80,567)	(8,040)		(266,108)
(Losses) gains on investment securities, net	18,768	5,644	77,006	[1]	172,236
Cost method accounting | Venture capital and private equity fund investments
Gain (Loss) on Investments [Line Items]
Recognized other-than-temporary impairment (OTTI) losses	$ 100	$ 300	$ 400		$ 700
Number of other-than-temporary impaired investments | Investment	4	5	19		22
Number of investments	270	281	270		281	281	281
Available-for-sale Securities
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	$ 46	$ 45	$ 2,971		$ 642
Gross losses on investment securities	(33)	(1,035)	(221)		(18,052)
Non-marketable securities | Fair value accounting | Venture capital and private equity fund investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	6,746	69,044	24,767		268,483
Gross losses on investment securities	(1,148)	(25,584)	(2,695)		(76,243)
Non-marketable securities | Fair value accounting | Other venture capital investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	15	6,779	198		11,334
Gross losses on investment securities	0	(1,233)	(52)		(3,274)
Non-marketable securities | Fair value accounting | Other securities
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	40	5,444	9,108		136,010
Gross losses on investment securities	(325)	(52,264)	(1,117)		(166,051)
Non-marketable securities | Equity method accounting | Venture capital and private equity fund investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	7,655	275	22,111		1,284
Gross losses on investment securities	(914)	(115)	(1,351)		(231)
Non-marketable securities | Equity method accounting | Debt funds
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	379	1,037	2,067		4,076
Gross losses on investment securities	(1)	(64)	(589)		(457)
Non-marketable securities | Equity method accounting | Other investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	1,282	927	2,147		3,635
Gross losses on investment securities	(460)	0	(1,470)		(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	5,624	2,641	21,101		7,706
Gross losses on investment securities	(132)	(272)	(530)		(781)
Non-marketable securities | Cost method accounting | Other investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	0	19	576		5,174
Gross losses on investment securities	$ (6)	$ 0	$ (15)		$ (260)

[1] Amounts for the nine months ended September 30, 2015, have been revised to reflect the retrospective application of new accounting guidance adopted in the second quarter of 2015 related to our consolidated variable interest entities (ASU 2015-02). Amounts prior to January 1, 2015 have not been revised for the adoption of this guidance. See Note 1— "Basis of Presentation” of the “Notes to Interim Consolidated Financial Statements (unaudited)” under Part I, Item 1 of this report for additional details.