Investments (Detail) (USD $)	3 Months Ended		9 Months Ended			1 Months Ended	0 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Aug. 23, 2013	Jan. 31, 2013 Again Faster LLC [Member]	Jul. 11, 2013 iGo, Inc. [Member] director	Sep. 30, 2013 iGo, Inc. [Member]	Aug. 23, 2013 iGo, Inc. [Member]	Jan. 31, 2013 Again Faster LLC [Member]	Sep. 30, 2013 Partnership [Member]	Jul. 31, 2013 Partnership [Member]
Sales of marketable securities	$ 20,400,000	$ 77,700,000	$ 65,474,000	$ 568,634,000
Percentage of voting interests acquired (as a percent)										40.00%
Cost of acquired entity, cash paid						4,000,000
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares									1,316,866
Equity Method Investment, Aggregate Cost									5,200,000			25,000,000
Equity Method Investment, Ownership Percentage, Outstanding Shares									44.00%
Ownership percentage (as a percent)					44.70%				44.70%
Number of directors appointed (in directors)							2
Number of directors on board (in directors)							4
Equity Method Investments								$ 4,000,000			$ 24,900,000