Components of Gains and Losses (Realized and Unrealized) on Investment Securities (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	$ 39,100		$ 60,108		$ 118,876		$ 197,671
Gross losses on investment securities	(18,872)		(7,846)		(65,000)		(22,392)
Gains (losses) on investment securities, net	20,228		52,262		53,876		175,279
Gains (losses) attributable to noncontrolling interests, including carried interest	12,776		42,961		34,616		112,783
Available-for-sale Securities
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	20		5		5,363		37,382
Gross losses on investment securities	121	[1]	0	[1]	1,771	[1]	94	[1]
Marketable Securities | Fair value accounting
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	255		470		3,874		912
Gross losses on investment securities	553		1,691		1,307		5,806
Non-marketable securities | Fair value accounting | Venture capital and private equity fund investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	28,639		34,640		88,037		117,344
Gross losses on investment securities	16,557		2,373		49,090		9,274
Non-marketable securities | Fair value accounting | Other venture capital investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	2,515		22,058		5,848		29,077
Gross losses on investment securities	125		3,351		10,007		5,015
Non-marketable securities | Fair value accounting | Other investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	0		0		21		20
Gross losses on investment securities	0		16		0		16
Non-marketable securities | Equity method accounting | Other investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	5,571		2,192		12,382		8,708
Gross losses on investment securities	1,091		50		1,794		1,359
Non-marketable securities | Cost method accounting | Venture capital and private equity fund investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	694		735		1,639		1,791
Gross losses on investment securities	423		365		963		797
Non-marketable securities | Cost method accounting | Other investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	1,406		8		1,712		2,437
Gross losses on investment securities	$ 2		$ 0		$ 68		$ 31

[1] The cost basis of available-for-sale securities sold is determined on a specific identification basis.