Investment Securities - Components of Gains and Losses (Realized and Unrealized) on Investment Securities (Detail) (USD $)	3 Months Ended
	Mar. 31, 2014 Investment		Mar. 31, 2013 Investment		Dec. 31, 2013 Investment
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	$ 238,220,000		$ 35,822,000
Gross losses on investment securities	(14,308,000)		(8,384,000)
Gains on investment securities, net	223,912,000		27,438,000
Fair value accounting | Other securities
Gain (Loss) on Investments [Line Items]
UnrealizedGainsRelatedToSingleInvestment	113,000,000
Realized Investment Gains (Losses)	46,100,000
Gross gains on investment securities	116,750,000	[1]	1,918,000	[1]
Gross losses on investment securities	(12,773,000)		(2,073,000)
Cost method accounting | Venture capital and private equity fund investments
Gain (Loss) on Investments [Line Items]
Recognized other-than-temporary impairment (OTTI) losses	100,000		500,000
Number of other-than-temporary impaired investments	7		16
Number of investments	282		309		288
Available-for-sale Securities
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	373,000	[2]	0	[2]
Gross losses on investment securities	(313,000)	[2]	(45,000)	[2]
Non-marketable securities | Fair value accounting | Venture capital and private equity fund investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	111,436,000		27,381,000
Gross losses on investment securities	(101,000)		(4,742,000)
Non-marketable securities | Fair value accounting | Other venture capital investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	2,582,000		2,640,000
Gross losses on investment securities	(744,000)		(464,000)
Non-marketable securities | Equity method accounting | Other investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	3,642,000		2,715,000
Gross losses on investment securities	(212,000)		(245,000)
Non-marketable securities | Cost method accounting | Venture capital and private equity fund investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	3,303,000		1,023,000
Gross losses on investment securities	(156,000)	[3]	(469,000)	[3]
Non-marketable securities | Cost method accounting | Other investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	134,000		145,000
Gross losses on investment securities	$ (9,000)		$ (346,000)

[1] Other securities (fair value accounting) and other venture capital investments include gains of $113.0 million, of which $46.1 million consists of realized gains, for the quarter ended March 31, 2014, attributable to one of our portfolio companies, FireEye. Our investment in FireEye is currently subject to a lock-up agreement. The extent to which any unrealized gains will become realized is subject to a variety of factors, including, among other things, the expiration of the current lock-up agreement to which the FireEye securities are subject, the actual sales of the securities and the timing of such actual sales.

[2] Includes realized gains (losses) on sales of available-for-sale securities that are recognized in the income statement. Unrealized gains (losses) on available-for-sale securities are recognized in other comprehensive income. The cost basis of available-for-sale securities sold is determined on a specific identification basis.

[3] Includes OTTI of $0.1 million from the declines in value for 7 of the 282 investments and $0.5 million from the declines in value for 16 of the 309 investments held at March 31, 2014 and 2013, respectively. We concluded that any declines in value for the remaining investments were temporary, and as such, no OTTI was required to be recognized.