Collateralized Transactions - Financial Instruments Owned and Pledged to Counterparties that Do Not Have Right to Sell or Repledge (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012
Collateralized Agreements [Line Items]
Collateral permitted to be delivered or repledged	$ 6,803,143		$ 52,261
Financial instruments owned, at fair value, pledged to counterparties that do not have the right to deliver or repledge	732,481	[1]	0	[1]
Assets Within Discontinued Operations [Member]
Collateralized Agreements [Line Items]
Financial instruments owned, at fair value, pledged to counterparties that do not have the right to deliver or repledge	$ 5,840,000

[1] Financial instruments owned, at fair value, pledged to counterparties that had the right to deliver or repledge includes $5.84 billion recorded within Assets within discontinued operations as of September 30, 2013.