Investments (Detail) (USD $)	12 Months Ended				1 Months Ended	12 Months Ended		0 Months Ended	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Aug. 23, 2013	Jan. 31, 2013 Again Faster LLC	Dec. 31, 2013 Again Faster LLC	Jan. 31, 2013 Again Faster LLC	Jul. 11, 2013 iGo, Inc. director	Dec. 31, 2013 iGo, Inc.	Aug. 23, 2013 iGo, Inc.	Dec. 31, 2013 Partnership	Jul. 31, 2013 Partnership
Schedule of Equity Method Investments [Line Items]
Proceeds from sales of marketable securities	$ 75,825,000	$ 574,074,000	$ 442,939,000
Percentage of voting interests acquired (as a percent)							40.00%
Cost of acquired entity, cash paid					4,000,000
Loss on equity-method investees	863,000	0	0			300,000			500,000
Shares of common stock acquired (in shares)										1,316,866
Total consideration										5,200,000		25,000,000
Ownership percentage acquired (as a percent)										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
Fair value of equity method investments											$ 26,000,000