Additional disclosures on cash flow information and non-cash activities (Parenthetical) (Detail) (USD $)					3 Months Ended
	Jun. 30, 2014		Dec. 31, 2013	Jun. 30, 2013	Jun. 30, 2014 Fixed Rate 700 Percent Notes Due July 2019 [Member]	Dec. 31, 2013 Fixed Rate 700 Percent Notes Due July 2019 [Member]
Schedule of Cash Flow, Supplemental [Line Items]
Senior Long Term Notes					$ 450,000,000	$ 0
Debt Issuance Costs					9,000,000
Securities Trades Receivables	$ 519,495,000	[1]	$ 71,680,000	$ 158,141,000	$ 441,000,000

[1] Includes $441 million of trades receivable as of June 30,2014, related to the issuance of $450 million in Senior Notes, which settled on July 1, 2014, net of debt issuance costs of $9 million.