Investment Securities - Components of Gains and Losses (Realized and Unrealized) on Investment Securities (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015 Investment		Mar. 31, 2014 Investment		Dec. 31, 2014 Investment
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	$ 96,609,000		$ 238,220,000
Gross losses on investment securities	(13,450,000)		(14,308,000)
(Losses) gains on investment securities, net	83,159,000		223,912,000
Fair value accounting | Other securities
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	19,601,000		116,750,000
Gross losses on investment securities	(994,000)		(12,773,000)
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		100,000
Number of other-than-temporary impaired investments	9		7
Number of investments	277		282		281
Available-for-sale Securities
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	2,690,000	[1]	373,000	[1]
Gross losses on investment securities	(94,000)	[1]	(313,000)	[1]
Non-marketable securities | Fair value accounting | Venture capital and private equity fund investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	58,489,000		111,436,000
Gross losses on investment securities	(11,635,000)		(101,000)
Non-marketable securities | Fair value accounting | Other venture capital investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	6,450,000		2,582,000
Gross losses on investment securities	0		(744,000)
Non-marketable securities | Equity method accounting | Other investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	4,188,000		3,642,000
Gross losses on investment securities	(588,000)		(212,000)
Non-marketable securities | Cost method accounting | Venture capital and private equity fund investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	4,833,000		3,303,000
Gross losses on investment securities	(134,000)	[2]	(156,000)	[2]
Non-marketable securities | Cost method accounting | Other investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	358,000		134,000
Gross losses on investment securities	$ (5,000)		$ (9,000)

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

[2] For the three months ended March 31, 2015 and 2014, includes OTTI losses of $0.1 million from the declines in value for 9 of the 277 investments and $0.1 million from the declines in value for 7 of the 282 investments, respectively. We concluded that any declines in value for the remaining investments were temporary, and as such, no OTTI was required to be recognized.